THERMOPHYSICAL PROPERTIES OF SILVER OXIDE DISPERSED IN SODIUM CHLORIDE

MOHAMED ASLAM BIN MOHAMED IQBAL

Supervisor: Dr. Hung Yew Mun

A Thesis submitted in partial fulfillment of the requirements for the

Degree in Bachelor of Engineering (Mechanical) Faculty of Engineering

Monash University

June 2013

ii

Certificate of Originality

I hereby declare that this submission is my own work and to the best of my knowledge it

contains no materials previously published or written by another person, nor material which

to a substantial extent has been accepted for the award of any other degree or diploma at

Monash University or any other educational institution, except where due

acknowledgement is made in the thesis. Any contribution made to the research by others,

with whom I have worked at Monash University or elsewhere is explicitly acknowledged in

the thesis.

I also declare that the intellectual content of this thesis is the product of my own work,

except to the extent that assistance from others in the project’s design and conception or in

style, presentation and linguistic expression is acknowledged.

…………………………………………………………..

(MOHAMED ASLAM BIN MOHAMED IQBAL)

iii

Acknowledgements

Firstly, I would like to express my gratitude to my supervisor for this project, Dr.

Hung Yew Mun for giving me an opportunity to do a research on this interesting project.

During the whole process of this research, Dr. Hung has given me guidance and corrected

my wrong in this experiment which has helped me to complete this research under his great

supervision.

Besides that, I would like to thank the mechanical lab assistant, Mr. Nasrun for

showing me how to use KD2Pro, Viscometer and pH meter which is essential in getting

more precise and accurate result and minimizing the error.

In addition, I would also like to thank another lab assistant which is Ms. Farisha for

guiding me in the preparation of my base-fluid (sodium chloride). Finally, I would like to

thanks all others who had provided me support to complete this project. Thank you.

iv

Abstract

Nanoparticles that are dispersed in base fluids are called nanofluids. Nanofluids are

formed by the colloidal suspension of nano sized particles in a base fluid. Common

nanoparticles that are being used are made of metals and oxides whereas the usual base

fluids used are water, organic solution and inorganic solution.

In this research, silver(I) oxide is used as nanoparticles and sodium chloride (NaCl)

solution with concentration of 1 mol is being used as base fluid. Thermophysical properties

that are being investigated in this reseach are thermal conductivity, viscosity and pH of

nanofluids. Nanofluids are synthesis using two-step method. Five data of thermal

conductivity, viscosity and pH are taken ranging from 30 to 80 degree celcius. Research

has been done on five different volume fractions of silver oxide-sodium chloride

nanofluids. The volume fractions that have been researched are 0.05%, 0.1%, 0.2%, 0.3%,

and 0.5%.

The result shows that as the temperature increases, the thermal conductivities of

nanofluids also increase. As for viscosity, it shows that the value drops as the temperature

increases. Finally as for pH, the value increases slightly as the temperature increases.

Besides that, different volume fraction also affects the thermal conductivity and viscosity

of the nanofluids. From the research it can be seen that as volume fraction increases,

thermal conductivities of the nanofluids increases as well. In addition, the viscosity also

increases as volume fraction increase. pH slightly decrease with increase in volume

fraction.

Highest enhancement achieved by this silver oxide and sodium chloride nanofluids

is 192.3%. This happens at volume fraction 0.5% and temperature 61.13 degree celcius.

Lowest viscosity achieved is 0.54 mPa.s which happens at volume fraction 0.05% and

temperature of 60.2 degree celcius. pH shows that nanofluids are in neutral state as they are

in the range of 6.98-7.2 for all volume fractions. This shows that combination of silver

oxide and sodium chloride exhibit an excellent thermoproperties.

v

Table of Contents

Certificate of Originality ....................................................................................................... ii

Acknowledgements ............................................................................................................... iii

Abstract .................................................................................................................................. iv

Table of Contents ................................................................................................................... v

List of Figures ..................................................................................................................... vii

List of Tables ......................................................................................................................... x

Chapter 1 ............................................................................................................................... 1

INTRODUCTION ..........................................................................................................................1

1.1 Background .......................................................................................................... 1

1.2 Problem Statement .............................................................................................. 4

1.3 Theory .................................................................................................................. 5

1.4 Project Objective and Hypothesis ...................................................................... 6

1.5 Project Outline ..................................................................................................... 7

1.6 Importance of Research ...................................................................................... 7

Chapter 2 ............................................................................................................................... 9

LITERATURE REVIEW ..............................................................................................................9

2.1 Overview .............................................................................................................. 9

2.2 Heat transfer process of Nanofluids .................................................................. 9

2.3 Thermal conductivity of Nanofluids ................................................................ 11

2.4 Viscosity of Nanofluid ....................................................................................... 21

2.5 pH of Nanofluids ................................................................................................ 24

2.6 Conclusion .......................................................................................................... 25

Chapter 3 ............................................................................................................................. 26

METHODOLOGY .......................................................................................................................26

3.1 Overview ........................................................................................................... 26

vi

3.2 Methodology ..................................................................................................... 26

Chapter 4 ............................................................................................................................. 28

EXPERIMENTAL SET-UP ........................................................................................................28

4.1 Overview ............................................................................................................ 28

4.2 Nanofluid ............................................................................................................ 28

4.3 Sonication ........................................................................................................... 34

4.4 Measuring apparatus ........................................................................................ 38

Chapter 5 ............................................................................................................................. 44

EXPERIMENTAL PROCEDURES ...........................................................................................44

5.1 Overview ............................................................................................................ 44

5.2 Sample preparation ........................................................................................... 44

5.3 Sonication Process ............................................................................................. 46

5.4 Data collection ................................................................................................... 48

5.5 Sonication time .................................................................................................. 52

Chapter 6 ............................................................................................................................. 53

RESULTS AND DISCUSSION...................................................................................................53

6.1 Overview ............................................................................................................ 53

6.2 Results ................................................................................................................ 53

6.3 Discussion ........................................................................................................... 68

6.4 Errors ................................................................................................................. 74

Chapter 7 ............................................................................................................................. 75

CONCLUSION .............................................................................................................................75

7.1 Conclusions ........................................................................................................ 75

7.2 Recommendation for future work ................................................................... 76

Chapter 8 ............................................................................................................................. 77

REFERENCES .............................................................................................................................77

APPENDICES .................................................................................................................... 83

vii

List of Figures

Figure 1: Number of `Nanofluids`, `Nanofluids and Heat Transfer`, ‘Nanofluid and

properties` research published in SCOPUS from 1993-2010 [16]. ..................................... 10

Figure 2 : Effect of temperature on thermal conductivity enhancement [31]. ..................... 16

Figure 3: The percentage of aluminum oxide nanofluids enhancement with different type of

base fluid [35]. ..................................................................................................................... 18

Figure 4 : Best enhancement for 3 different particle sizes at 3 different temperatures [37]. 19

Figure 5 : Sodium chloride................................................................................................... 29

Figure 6: Distilled water ...................................................................................................... 30

Figure 7: Magnetic Stirrer .................................................................................................... 30

Figure 8 : Parafilm ............................................................................................................... 31

Figure 9 : Aluminium foil .................................................................................................... 32

Figure 10 : Nanofluids covered with aluminium foil before sonication .............................. 32

Figure 11 : Silver(I) oxide nanoparticles in the bottle ......................................................... 33

Figure 12 : Silver(I) oxide nanoparticles in powder form ................................................... 33

Figure 13: Ultrasonic Processor with probe ......................................................................... 35

Figure 14: Ultrasonic processor sonication setting. ............................................................. 35

Figure 15 : Ultrasonic probe ................................................................................................ 36

Figure 16: Sound Enclosure ................................................................................................. 37

Figure 17 : Weighing machine Fx-3000i ............................................................................. 38

Figure 18: KD2 Pro device .................................................................................................. 40

Figure 19: KS-1 sensor needle ............................................................................................. 40

Figure 20: The SV-10 Vibro Viscometer ............................................................................. 41

Figure 21: Sensor plate and temperature sensor .................................................................. 42

Figure 22: PB-10 Standard pH meter. .................................................................................. 43

Figure 23: Conical-bottom centrifuge tube .......................................................................... 43

Figure 24 : Nanoparticles in base fluids prepared................................................................ 46

Figure 25 : Ultrasonic probe tip at the centre of nanofluid .................................................. 47

Figure 26 : Sonication process ............................................................................................. 47

Figure 27 : 5 hours sonication time ...................................................................................... 47

viii

Figure 28: KD2 Pro Verification Standard Glycerin ........................................................... 49

Figure 29: KS-1 sensor needle placed at the centre of the base fluid .................................. 49

Figure 30: Correct set up to take viscosity data ................................................................... 51

Figure 31: Picture above shows pH Buffer Solution. .......................................................... 52

Figure 32: pH Electrode fully immersed in base fluid. ........................................................ 52

Figure 33: Effect of temperature on thermal conductivity of 0.05% volume fraction of

Ag2O-NaCl nanofluid .......................................................................................................... 54

Figure 34: Effect of temperature on viscosity of 0.05% volume fraction of Ag2O-NaCl

nanofluid .............................................................................................................................. 55

Figure 35: Effect of temperature on pH of 0.05% volume fraction of Ag2O-NaCl nanofluid

.............................................................................................................................................. 56

Figure 36: Effect of temperature on thermal conductivity of 0.1% volume fraction of Ag2O-

NaCl nanofluid ..................................................................................................................... 57

Figure 37: Effect of temperature on viscosity of 0.1% volume fraction of Ag2O-NaCl

nanofluid .............................................................................................................................. 58

Figure 38: Effect of temperature on pH of 0.1% volume fraction of Ag2O-NaCl nanofluid

.............................................................................................................................................. 59

Figure 39: Effect of temperature on thermal conductivity of 0.2% volume fraction of Ag2O-

NaCl nanofluid ..................................................................................................................... 60

Figure 40: Effect of temperature on viscosity of 0.2% volume fraction of Ag2O-NaCl

nanofluid .............................................................................................................................. 61

Figure 41: Effect of temperature on pH of 0.2% volume fraction of Ag2O-NaCl nanofluid

.............................................................................................................................................. 62

Figure 42: Effect of temperature on thermal conductivity of 0.3% volume fraction of Ag2O-

NaCl nanofluid ..................................................................................................................... 63

Figure 43: Effect of temperature on viscosity of 0.3% volume fraction of Ag2O-NaCl

nanofluid .............................................................................................................................. 64

Figure 44: Effect of temperature on pH of 0.3% volume fraction of Ag2O-NaCl nanofluid

.............................................................................................................................................. 65

Figure 45: Effect of temperature on thermal conductivity of 0.5% volume fraction of Ag2O-

NaCl nanofluid ..................................................................................................................... 66

ix

Figure 46: Effect of temperature on viscosity of 0.5% volume fraction of Ag2O-NaCl

nanofluid .............................................................................................................................. 67

Figure 47: Effect of temperature on pH of 0.5% volume fraction of Ag2O-NaCl nanofluid

.............................................................................................................................................. 68

Figure 48 : Effect of volume fraction and temperature on thermal conductivity of Ag2O-

NaCl nanofluid ..................................................................................................................... 69

Figure 49 : Enhancement of thermal conductivity ............................................................... 70

Figure 50 : Viscosity of Ag2O-NaCl nanofluid at different volume fraction and temperature

.............................................................................................................................................. 71

Figure 51 : pH of nanofluids with different volume fraction at different temperature ........ 72

Figure 52 : Sedimentation after 4 hours ............................................................................... 73

x

List of Tables

Table 1: Summary of literature review on effect of volume fraction on thermal conductivity

.............................................................................................................................................. 13

Table 2: Mass of silver oxide for different volume fraction ................................................ 45

Table 3: Calibration using KD2 Pro Verification Standard Glycerin .................................. 48

Table 4: Calibration using distilled water ............................................................................ 50

Table 5: Calibration using pH buffer solution of 7 .............................................................. 51

1

Chapter 1

INTRODUCTION

1.1 Background

One of the most important processes in either mechanical, electrical, biological or

chemical industry is the heat transfer process. Heat transfer is involved in many operations

in industry such as heating and cooling, materials processing, and machines thermal

management. Therefore, if the performance of heat transfer can be enhanced and improved

further, there can be vast amount of energy saving in the industry, reduction in production

time and increase in machines life span. This will bring a lot of benefit to the manufacturer

as production efficiency will increase. A lot of research has been done to improve the

current process of heat transfer. One of the researches that have been done is on nanofluid.

Nanofluid is a fluid that consists of nanoparticle which is being dispersed in a base

fluid. Common nanoparticles that are being used during research nowadays are

aluminum(III) oxide (Al2O3), copper(II) oxide (CuO), zinc(II) oxide (ZnO), silicone(IV)

oxide (SiO2), and titanium(IV) oxide (TiO2) whereas common base fluid used are the

organic base fluid ethylene glycol, oil and inorganic base fluid, water [1]. From research, it

is known that most nanofluids have superior thermo-physical properties which includes

thermal conductivity and viscosity than the its base fluid such as water [2]. This shows that

nanofluids have high potential to replace the current fluid used in heat transfer industry.

There has been much research done to create different kind of nanofluids in order to

improve the common base fluid heat transfer performance. These experimental studies has

been done by many since the work of Maxwell [3] who presented the theory of effective

thermal conductivity of suspension calculation. There are so many findings on nanofluids

as it is now after years of research and experiments done since his theory is presented.

2

Nanofluids are the colloidal suspensions of nano-sized oxide or metals that have

been dispersed in base fluids. The efficient size of nano-sized oxide or metals is below 100

nanometers where it can be dispersed stably in the base fluid. Nanofluids are proven to

enhance the heat transfer performance of base fluid greatly [4]. The suspended nano-sized

oxide or metal will increase the thermal conductivity of the newly formed fluid hence

giving the fluid higher capability in their heat exchanging process for more efficient heat

transfer processes. The development on nanofluids can help the industries in reducing the

size of thermal equipment which will bring a healthy competition between companies to

develop a high performance fluid.

The level of nanofluids heat transfer enhancement is determined by few

modification. For instance, different volume fraction of nanoparticles dispersed in the

chosen base fluid will give different level of enhancement to the nanofluids thermal

conductivity and so does the nanoparticles size [5]. According to Maxwell`s [3] theory, the

suspension of solid particles in base fluid can improve the thermal conductivity of the fluid

because it is known that solid have a higher magnitude of thermal conductivity than liquid.

Nevertheless, one of the problem he did not account in is theory is the size of coarse

particle. Coarse particles is big hence they have higher chance of encountering

sedimentation which will increase the resistance in the fluid`s flow and can cause erosion.

That is when scientist tries to reduce the size of coarse particles and they have tried to do

experiments using nanoparticles.

During research, most of the scientist and engineer will use volume fraction as

small as 0.01% up until as big as 20% of nanoparticles to investigate the heat transfer

enhancement of nanofluids. The readings of thermo-physical properties such as the

viscosity and thermal conductivity are taken during experiment. These properties

combination play an important role in the enhancement and decrement of fluids heat

transfer capabilities. Besides that, pH of the nanofluids is taken as well to investigate the

behavior and stability of the newly formed fluid. Low pH fluid form will exhibit acidic

3

behavior which can cause corrosion while neutral pH will behave like water and high pH

will have behavior of alkaline fluid.

Basically there are many ways to produce nanoparticles. One of the common ways

is by laser pyrolysis. Laser pyrolysis is a gas phase process which is used to produce nano-

sized metals and oxides. Average size of nanoparticles produced by laser pyrolysis is 10-

200nm. Besides that there are several other ways to produce nanoparticles which can be

grouped as liquid-phase method, inert-gas condensation method, mechanical grinding, sol-

gel process, and hydrothermal method [6]. They are all used to produce different type of

nanoparticles.

As for nanofluids, there are two common ways to produce them which are two-step

technique and one-step technique. In two-step method, there will be two steps in preparing

the nanofluid. First step is the production of nanoparticles in dry form. After dry

nanoparticles are produced, they will be dispersed into the base fluid used in the research

which is the second step. Two-step method works well with oxide nanoparticles and

nanoparticles with high volume concentration but less efficient with metal nanoparticles

[7]. The challenge encounter in this method is aggregation during experiment which is

caused by the high surface energy of nanoparticles. This problem is hard to overcome but

can be reduced by using ultrasound and high shear technique [8]. Besides that,

nanoparticles that have gone through surface treatment also showed some excellent ability

in dispersion and does not aggregate [9].

Single step technique on the other hand is a technique where nanoparticles are

manufacture and nanofluids are prepared simultaneously. This method uses physical vapor

deposition (PVD) technique where dry nanoparticles are condensed directly in a flowing

low vapor-pressure fluid [8]. The nanofluids formed using one-step technique display a

much better characteristic in dispersion of nanoparticles as less agglomeration occurs and

the nanofluid is more stable [4]. Nevertheless, two-step technique is more popular because

one-step technique cannot be used to mass produce which reduces its commercial value

[10].

4

For this research project, the thermo-physical properties which include thermo

conductivity, viscosity and pH of nanofluids will be analyzed. The nanoparticles that is

being used in this experiment is silver(I) oxide (Ag2O) with average size around 60 nm.

Base fluid chosen for this experiment is sodium chloride which is prepared in lab. The

concentration of sodium chloride used is 1 mol. The experiment would look at the effect of

different volume fraction of nanoparticles at different temperature on thermo-physical

properties of nanofluid.

1.2 Problem Statement

Technologies are getting more advance every day. The growth in technology is so

fast and device produced is getting smaller. Therefore one of the biggest challenges that

grow with the growth of technology is heat transfer management. Heat transfer occurs in

many industries electronics, lighting, manufacturing or transportation. Overheat seems to

be a problem for most device. The conventional way to manage heat is by using heat

transfer fluid to exchange heat and provide cooling. As production is getting bigger, the

area of heat exchanging process to manage the heat needs to be increased to sustain the

bigger production of devices which is undesirable. Therefore there is an urge for a better

performance heat transfer fluid and researches on nanofluids is being proposed to overcome

the problem.

Many researches have been done on nanofluids. Most of them are using organic

solutions as base fluids which are water, oil and ethylene glycol. The results are then

tabulated for different volume concentration at different temperature for different particle

size. Although there have been a lot of findings by a lot of research, the data have no

generalize equation to generalize the findings as data will not have the same trend for

different volume faction, different particle size and different method used to produce the

nanofluid. Hence to find the best performance fluid more variety of research needs to be

done. Besides that, most of the research done is by using organic solution as base fluid and

water. Since there is little research done on dispersion of nanoparticles in inorganic

5

mixtures, a trial with sodium chloride as inorganic base fluid is being experimented. The

thermo-physical properties of the nanofluids formed are being analyzed as it gives the best

insight on the nanofluid heat transfer capabilities

1.3 Theory

1.3.1 Volume Fraction

Volume fraction can be defined as volume of a constituent which will be divided by

total volume of a mixture [11]. In this research, volume fractions are being presented in

percentage and can be calculated as follow:

( )

(1.1)

1.3.2 Density

Density can be defined as heaviness of an object at a constant volume. Density can

be calculated by dividing mass to the volume [12]. In this experiment, density is used to

calculate the mass of nanoparticles that will be used to form the nanofluids according to the

volume fraction chosen. The equation of density is as follow:

(1.2)

1.3.3 Enhancement

Enhancement can be defined as improvement value of an object`s properties. In this

experiment, enhancement of thermal conductivity is calculated in percentage by dividing

the difference of thermal conductivity of nanofluids and the base fluids then dividing them

with the thermal conductivity of base fluid at respective temperature before multiplying

6

them by hundred to get the percentage. The temperatures have the difference of ± 1 degree

celcius. The equation is as follow:

( ) –

(1.3)

1.4 Project Objective and Hypothesis

1.4.1 Objective

The main objective of this research project is to investigate the thermo-physical

properties which are thermal conductivities and viscosities of nanofluid that is formed by

dispersing silver oxide in sodium chloride solution at different temperatures using five

different volume fractions. The volume fractions that are to be investigated are 0.05%,

0.1%, 0.2%, 0.3% and 0.5%. Besides that, pH of the nanofluid formed also is being

investigated.

Another objective is to compare the thermal conductivity and viscosity of the

nanofluids formed and inorganic base fluid, sodium chloride with no nanoparticles

suspended in the fluid. The thermal conductivity and viscosity are taken five times in the

range of 30 degree celcius to 80 degree celcius.

1.4.2 Hypothesis

After doing some readings on some research projects which are relevant to this

project, hypotheses are made in line with the project objective. The hypotheses made are as

follow:

1. It is expected that thermal conductivity and will increase as the temperature of

nanofluid increases.

2. It is expected that viscosity will decrease as the temperature of nanofluid increases.

7

3. It is expected that thermal conductivity and viscosity will increase when the volume

fraction of nanoparticles in nanofluid increases.

4. It is expected that thermal conductivity and viscosity of nanofluid is much higher

than the thermal conductivity and viscosity of the base fluid as temperature

increases.

5. The pH is expected to have little changes as temperature and volume fraction

increases.

1.5 Project Outline

This project will focus on effect of volume fraction on the thermal conductivity and

viscosity of the nanofluid. As there is no literature on silver oxide being dispersed in

sodium chloride, this research will emphasize more on the trend of the thermal conductivity

and viscosity when temperature rises and when the volume fraction changes. The

experimental data will be presented in the form of graph based on the data acquired during

the experiment. The data will be compared to the existing literature on silver nanofluids

that uses different kind of base fluid.

1.6 Importance of Research

The growth in technologies in the industry has increase the need for more efficient

cooling system than the conventional cooling system. As technologies are getting more

advance and devices are getting smaller and smaller each day hence the needs for better

heat management has been one of the most important aspect to look into. It plays an

important role in ensuring their performance. There are some interests in extended surface

thermal technologies such as fins that are used to improve the efficiency of cooling fluids

but the improvement is limited. Hence, this has called on the research on nanofluids.

8

Nanofluids have shown big potential in heat transfer enhancement and have the

ability to replace the conventional fluid used in heat transfer process which includes water,

oil and ethylene glycol. Nanofluids are made by dispersion of nanoparticles inside a base

fluid. They are known to have higher thermal conductivity than the normal base fluid. High

thermal conductivity of nanofluids will improve the process efficiency of equipment and

increase the life span of equipment as there will be less thermal limitation on them.

Therefore research on nanofluid is important to cope with the growth of industry and the

miniaturization of devices.

9

Chapter 2

LITERATURE REVIEW

2.1 Overview

This part of thesis will cover the researches that have been done by previous

researchers on nanofluids that will help to gain the basic knowledge of nanofluids in order

to complete this research project. Besides that, literature review also is used as guidance to

validate the trend of results obtained in the experiment. The early part of the literature

review is organized by general topics on heat transfer before the topics that are related to

the research objective is being covered. These topics are important to complete the analysis

of the result.

2.2 Heat transfer process of Nanofluids

The growth of technology has called on to the replacement of the traditional

transport fluid like water. One of the potential fluid that has been discovered by scientist

and engineers as its replacement is nanofluid. Nanofluid is one of the challenges in science

world in order to solve thermal management issue that has been encountered in these

technology savvy days. Nanofluids have shown some interesting signs in its ability to

enhance the quality of heat transfer due to their excellent characteristics. Therefore many

researches has been done to get nanofluids as the new transport fluid in medium that are

using fluid as heat transfer medium. There are a few of researches that have shown

promising results of nanofluid heat transfer enhancement.

10

For example, Eastman et al. [13] reported a 15% increment of heat transfer

coefficient when copper oxide is dispersed in pure water compared to the pure water

without nanoparticles. The volume fraction used in the experiment is 0.9%.. There are also

several other research that shows that with low volume fraction of nanoparticles in base

fluid can enhance the heat transfer performance of nanofluid by almost 20% [14]. This

proves that nanofluids hold a great potential as heat transfer medium to replace the

conventional fluids.

Despite the potential that has been shown by nanofluids in the transfer enhancement

ability, they cannot be used as heat transfer medium yet. This is because there are still

problems in sedimentation and shearing flow when preparing nanofluids [15]. Besides that

the research done is still in primary stage and most of the research still lies on basic

knowledge of the nanofluids [14]. There are still little references on nanofluid properties

and heat transfer performance of nanofluids that have been published. Below is the chart

that shows research that has been published from 1993 until 2010 in SCOPUS database:

Figure 1: Number of `Nanofluids`, `Nanofluids and Heat Transfer`, ‘Nanofluid and

properties` research published in SCOPUS from 1993-2010 [16].

0 50 100 150 200 250

1993

1995

1996

1997

1999

2000

2001

2002

2003

2004

2005

2006

2007

2008

2009

2010

Nanofluids

Nanofluidsand HeatTransfer

Nanofluidsandproperties

11

From figure 1 we see that the number of research in nanofluids and heat transfer as

well as nanofluids properties has increased a lot in recent years from 2005. It will keep

growing as more research on nanofluids heat transfer and nanofluids properties should be

done in order to understand the behavior of the nanofluids and be ready to be used in the

industry.

2.3 Thermal conductivity of Nanofluids

Thermal conductivity is one of the important thermo-physical properties to be

researched on in nanofluid. Usually the addition of nanoparticles in base fluid will result in

increment of thermal conductivity. The extent of thermal conductivity increment is affected

by few factors such as volume fractions, particles size, type of base fluids and temperature

[17]. Therefore in this section of literature review, study of these factors will be done to

give more understanding towards how thermal conductivity of nanofluids are affected

which is important for this research project.

2.3.1 Effects of Volume Fraction on Thermal Conductivity of Nanofluids

Many studies have been done to study the effect of volume fraction on the thermal

conductivity of nanofluids. First ever study of thermal conductivity which are done Masuda

et al. [18]. They used Al2O3 as nanoparticles and water as base fluid to prepare the

nanofluids. Nanoparticles are suspended in the base fluid by using two-step nanofluid

preparation method. In this study, they found that by using volume fraction of 4.3% at

31.85 degree celcius, thermal conductivity of nanofluids has been increased as much as

32.4% which is very high. They also found a trend which shows that as volume fraction

increases, the thermal conductivity of nanofluids increases as well. More research has been

done since their findings on this.

12

Li and Peterson [19] also have conducted an experiment to investigate the effect of

volume fraction on nanoparticles. In his experiment, he uses Al2O3 as nanoparticles and

water as base fluid as well. He prepared nanofluids with 2%, 4%, 6%, 8%, and 10%

volume fraction. The results again show that as volume fraction increases, thermal

conductivity of nanofluids increases together with it. Result from the experiment is that at

10% volume fraction of Al2O3 suspended in water at temperature of 34 degree celcius,

enhancement of 30% in thermal conductivity of nanofluid is observed.

Besides that, Hong et al. [20] have conducted an experiment using iron

nanoparticles and dispersing them into ethylene glycol solution. The result again shows that

with increasing number of volume fraction, the higher thermal conductivity of the

nanofluids become. The highest enhancement of iron nanoparticles in this experiment is at

volume fraction of 0.55% which gives 18% enhancement. The iron nanoparticles in this

case are being prepared using chemical vapor condensation process. Then the nanofluids

are prepared using two step methods.

As for silver nanofluids, not many experiments has been conducted to find the

thermal conductivity of them. There is an experiment has been conducted by Lee et al. [21]

with silver as nanoparticles and two base fluids are used as base fluids which are

water/ethylene glycol mixture and water/ammonia mixture. The experiment is done using

two-step method and it is observed that increment in volume fraction results in increment

of thermal conductivity.

There are few others research that has been done by researchers and most of them

found consistent result that as volume fraction increase, thermal conductivity of nanofluids

increase as well. All the research findings can be tabulated and summarize as shown table

below:

13

Table 1: Summary of literature review on effect of volume fraction on thermal conductivity

Source Nanofluids Volume

fraction (%)

Best

enhancement

(%)

Masuda et al.

[18] Al2O3 / Water 1.3 - 4.3 32.4

Li and Peterson

[19] Al2O3 / Water 2.0 – 10.0 30

Hong et al. [20] Fe / Ethylene

Glycol 0.1 – 0.55 18

Lai et al. [22] Al2O3 / Water 0 – 1.0 8

Jung et al. [23] Al2O3 / Water 0.5 – 1.8 32

Yi-Min and

Xuan [24] Cu / Water 0.5 – 2.0 39

Ding et al. [25] MWCNT /

Water 0.1 – 1.0 350

Wen and Ding

[26] Al2O3 / Water 0.6 – 1.6 42

14

From the table summarize, it the best enhancement all happens at highest volume

fraction from the range except for Ding et al. [25] research as the 350% enhancement of

multi wall carbon nanotubes(MWNCT)/water nanofluid happens at volume fraction of

0.5%. The researchers reckon that the inconsistency of the results happen because of the

interaction between the walls of nanotubes during experiment. Besides that, the study done

by Murshed et al. [27] also gives an inconsistent results. They used hot-wire method to

determine the thermal conductivity of titanium oxide/water nanofluids which are varied

between 0.5% - 5% volume fraction. Result shows inconsistent trend in the thermal

conductivity of the nanofluids especially at low volume fraction. The researchers reckon

that either addition of cetyltrimethyl ammonium bromide (CTAB), long sonication time or

hydrophobic surface force might be the reason behind the inconsistent behavior. Therefore

we can conclude that thermal conductivity increases together with volume fraction for most

cases.

2.3.2 Effects of Temperature on Thermal Conductivity of Nanofluids

Different temperatures will give different thermal conductivity reading.

Temperature changes will change the kinetic energy of particles and atoms of nanofluids

hence giving a different reading of thermal conductivity [28].

An experiment has been conducted by Ravikanth and Debendra [29] on effect of

temperature on thermal conductivity. They used two-step method to prepare the nanofluids.

copper oxide is used as nanoparticle and mixture of ethylene glycol and water is used as

base fluid with 60:40 ratios. From the experiment, they have found that thermal

conductivity increase by 22.4% at temperature of 25 degree celcius and as temperature

increase the thermal conductivity increases as well. The highest temperature used is 90

degree celcius and have the highest enhancement with 47.8% of enhancement. Their

experiment shows that increase in temperature of nanofluids will increase their transfer

conductivity as well.

15

Besides that, Ghosh et al. [30] have done a study on effect of temperature on

copper-aluminum(Cu9Al4) nanofluids on thermal conductivity. In this experiment, they

have used copper-aluminum nanoparticles with the size of 4 nm diameter and water as base

fluid. Nanofluids with 0.48% volume fraction are prepared using two-step method. In the

experiment, they have found that as temperature increases, the thermal conductivity

enhacement increase as well. At temperature of 25 degree celcius, enhancement is about

90% and as it increases to about 43 degree celcius, the enhancement increases to about

105%. The highest temperature where data is taken is at about 55 degree celcius and the

enhancement shows is about as high as about 120%. This shows that as temperature

increase, thermal conductivity increases as well.

Walvekar et al. [31] also has conducted an experiment on effect of temperatures on

thermal conductivity enhancement. In their experiment, they use carbon nanotubes (CNT)

as nanoparticles and water as base fluids. They have also added gum arabic(GA) as

stabilizer in this experiment to form carbon nanotubes nanofluid. The volume fractions of

0.01%, 0.02%, 0.04%, 0.08% and 1% are used in their experiment. The temperatures are

set to be from 25 degree celcius until 60 degree celcius. The results they have found is as

follow:

16

Figure 2 : Effect of temperature on thermal conductivity enhancement [31].

As shown in figure 2, they have found that at every volume fraction, as temperature

increases, the enhancement of thermal conductivity increases as well. The highest

enhancement of 287.5% is observed at temperature of 60 degree celcius for 0.1% volume

fraction. Therefore we can conclude that for most cases in nanofluids research, thermal

conductivity will increase as temperature increase.

2.3.3 Effects of Base Fluids on Thermal Conductivity of Nanofluids

Different base fluids have different thermal conductivity. When preparing

nanofluids, nanoparticles will be dispersed in a base fluid. Therefore, depending on the

base fluids used, the thermal conductivity enhancement will be different. The difference

happens because of viscosity of base fluid will affects the Brownian motion of

nanoparticles and resulting in changes of thermal conductivity [32].

0

50

100

150

200

250

300

350

0.01 0.02 0.04 0.08 0.1

Enh

ance

me

nt

(%)

volume fraction (%)

Effect of temperature on thermal conductivity enhancement

25 º C

30 º C

40 º C

50 º C

60 º C

17

There has been an experiment done by Beck et al. [33] on effects of different base

fluid on alumina nanofluids. In this experiment, they have used water, ethylene glycol and

mixture of ethylene glycol with 50:50 ratios as base fluid. The thermal conductivity are

measured using hot-wire method. In this experiment, the alumina nanoparticles used have

an average size of 12 mm. The result shows that the highest enhancement is when alumina

is dispersed in ethylene glycol followed by ethylene glycol/water mixture and finally water.

This shows that different base fluid does give different type of enhancement.

Besides that, an experiment is done by Wang et al. [34] on alumina and copper

oxides nanoparticles dispersed in four different base fluids which are water, ethylene

glycol, vacuum pump fluid and engine oil. For alumina nanoparticles, the best

enhancement happens when it is dispersed in ethylene glycol followed by engine oil and

water. The lowest enhancement happens in vacuum pump base fluid. As for copper

nanoparticles, the base fluids that they tested with are only ethylene glycol and water. In

this case it has been concluded that both base fluid gives about the same enhancement to

the thermal conductivity. These again show that base fluid does affect thermal conductivity

enhancement but it is not necessarily one base fluid is superior to another. It depends on

nanoparticles reaction towards the base fluid.

Xie et al. [35] also have conducted an experiment to analyze the effect of base

fluids on thermal conductivities of nanofluids. In their experiment, they used hot-wire

method to determine thermal conductivity of nanofluid. Nanoparticles used in the

experiment are aluminum oxide with volume fraction of 5%. The base fluids used in the

experiment are water, glycerol, ethylene glycol, and pump oil. The results can be

summarized as below:

18

Figure 3: The percentage of aluminum oxide nanofluids enhancement with different type of

base fluid [35].

As shown in figure 3, the best enhancement happens when aluminum oxide is

dispersed in pump oil followed by ethylene glycol, glycerol and water respectively. Besides

that, it is also found in this experiment that the thermal conductivity enhancement is lower

for higher base fluid initial thermal conductivity. This experiment is consistent with

Maxwell`s [3] theory.

Liu et al. [36] have conducted an experiment with using multi walled carbon

nanotubes (MWCNT) nanoparticles as nanoparticles with ethylene glycol and synthetic

engine oil as base fluid. In this experiment, hot-wire method are used to measure thermal

conductivity. The experiment shows that the MWCNT/synthetic engine oil nanofluids have

a bigger enhancement than the MWCNT/ethylene glycol nanofluids. MWCNT/synthetic

engine oil nanofluids have thermal enhancement of 30% whereas MWCNT/ethylene glycol

nanofluids have 12.4% of thermal conductivity.

0 5 10 15 20 25 30 35 40

Al2O3 + Water

Al2O3 + Glycerin

Al2O3 + Ethylene Glycol

Al2O3 + Pump Oil

Type of Nanofluids and Enhancement (%)

19

All these research have proven that type of base fluid does affect the thermal

conductivity of nanofluids forms. Hence more combination of nanoparticles and base fluids

can be researched on to find the best combination to be used in industry.

2.3.4 Effects of Particle Size on Thermal Conductivity of Nanofluids

Particles size of nanoparticles play an important role in determining thermal

conductivity of nanofluids. There are ranges of different sizes of nanoparticles used in

preparation of nanofluids but the effective size is below 100nm.

An experiment has been conducted by Teng et al. [37] on effect of aluminum oxide

particle size on thermal conductivities of Al2O3 / Water nanofluids. Two-step method is

used to produce the nanofluids in this experiment and particles sizes used are 30 nm, 50nm

and 100nm. The experiment is done at three different temperatures which 10 degree

celcius, 30 degree celcius and 50 degree celcius. The results can be summarized as follow:

Figure 4 : Best enhancement for 3 different particle sizes at 3 different temperatures [37].

0

2

4

6

8

10

12

14

16

10 30 50

Be

st e

nch

ance

me

nt

(%)

Temperature (Celcius)

Best enhancement for different particles size

100 nm

50 nm

30 nm

20

From figure 4, it can be seen that at every temperature, particles size of 30 nm gives

the best enhancement to the thermal conductivity of nanofluids formed. This is because as

the size of particle become smaller, the surface area of solid-liquid interface is bigger.

Hence more collisions happen among particles resulting in higher Brownian motion

creating a higher value of thermal conductivity.

Chopkar et al. [38] studied the effect of particles size on thermal conductivity of

Al2Cu and Ag2Al nanoparticles using two different base fluid which are water and ethylene

glycol. In their research, they used 30nm and 120nm nanoparticles. Nanofluids are

prepared using two-step method and thermal conductivity is determined by hot-wire

method. For both base fluid, Al2Cu and Ag2Al nanoparticles with 30nm shows greater

thermal conductivity enhancement than 120nm nanoparticles. This again shows that

smaller nanoparticles resulted in higher enhancement.

There is also a research done by Mintsa et al. [39] on effect of particle size on

thermal conductivity of nanofluids. In their experiment, aluminium oxide is used as

nanoparticle and water is used as base fluid. Aluminium oxides used have the size of 36 nm

and 47 nm. The nanofluids are prepared using two-step method and thermal conductivities

are taken in the range from 20 degree celcius to 50 degree celcius. In their experiment, they

observed that at room temperature, the thermal conductivity of both particle size has about

the same thermal conductivities. Nevertheless, as temperature increase, the nanofluids

prepared with aluminium oxide with size of 36nm shows higher enhancement than

nanofluids prepared with aluminium oxide with the size of 47 nm. Hence this again shows

that smaller particle size increase thermal conductivity of nanofluids.

Therefore, we can conclude that in most cases of nanofluids research it can be

observed that thermal conductivity of nanofluids increases as particle size decrease. This

happens in most of the experiments done by researchers.

21

2.4 Viscosity of Nanofluid

Viscosity is one of important properties in nanofluids. This determines the behavior

of nanofluids if they are to be applied in real application since viscosity affects the pressure

drop during convection. Similar to thermal conductivity, viscosity are affected by some

parameters which are volume fraction of nanoparticles used to form the nanofluids,

temperature of nanofluids and also particle size of nanoparticles used during the synthesis

of nanofluids. [17].

2.4.1 Effects of Volume Fraction on Viscosity of Nanofluids

Different volume fraction of nanoparticles dispersed in base fluids will form

nanofluids of different volume fractions. This is because addition of nanoparticles will

disrupt the attraction between molecules in the base fluids.

There are limited amount of studies that has been done on effect of volume fraction

on viscosity. There is a study done by Wang et al. [34] to measure the effect of volume

fraction on viscosity. He uses two nanofluids in his study which are aluminum oxide

nanoparticles and water as base fluid and also aluminum oxide as nanoparticles and

ethylene glycol as base fluids. In their study, it shows that as volume fraction of aluminum

oxide increases in base fluids, the viscosity also increases as well. This happens for both

nanofluids that they have prepared.

Besides that, Das et al. [40] also has done an experiment using aluminium oxide as

nanoparticles and water as base fluids. In their experiment, they have found that increase in

volume fraction also increase the viscosity of nanofluids. Besides that, they also have

deduced the possibility of nanofluids having non-Newtonian and viscoelastic behaviour in

some cases. Therefore more study on viscosity of nanofluid need to be done before they

can be used in real application.

Ding et al. [25] has done a research using carbon nanotubes as nanoparticles and

water as base fluids. They found out that viscosity of nanofluids formed increase as volume

22

fraction increase. Besides that, they also found that there are shear thinning behaviour in

nanofluids where shear rate are higher at the wall which indicates its ability to provide a

good fluid flow performance.

Therefore in can be concluded that as volume fraction increases, viscosity of

nanofluids also increase. This trend is almost the same for most cases done by few

researchers.

2.4.2 Effects of Temperature on Viscosity of Nanofluids

As temperature changes, the viscosity of nanofluids also change. There are many

researches that have shown that temperature increase can reduce the viscosity of

nanofluids. This is because as temperature increase, the molecular attraction of nanofluids

atoms are affected hence reducing the viscosity of nanofluids.

Yang et al. [41] have conducted an experiment to observe the effect of temperature

on viscosity. In their experiment, they have used graphite with volume fraction of 2% as

nanoparticles and automatic transmission fluid (ATF) as base fluid. The experiments are

done using four different temperatures which are 35, 43, 50 and 70 degree celcius. They

found that as temperature increase, the viscosity of nanofluids formed decreased. The

highest viscosity is at 35 degree celcius and the lowest viscosity is at 70 degree with the

value of 41.4 mm2·s

−1 and 12.2 mm

2·s

−1 respectively.

Besides that, Anoop et al. [42] also has done a study on effect of temperature on

viscosity. In their experiment, three nanofluids are used which are combination of copper

oxide and ethylene glycol, aluminum oxide and ethylene glycol, and aluminum oxide and

water. They uses volume fraction of 0.5%, 1%, 2%, 4%, and 6% and regulate the

temperature from 20 to 50 degree celcius. They have found that all three nanofluids at

every volume fractions have the same trend which is as temperature increases, the viscosity

of nanofluids decreases.

23

Namburu et al. [43] research shows that viscosity decreases exponentially with the

increment of temperature. They use copper oxide ranging from 0 to 6.12% volume fraction

as nanoparticles and mixture of ethylene glycol with water as base fluids. In their

experiment, they have used temperature in the range from 35 to 50 degree celcius. Besides

that, they also found that nanofluids acts like a Newtonian fluids in that range of

temperature.

Therefore it can be concluded that as temperature increases, viscosities of the

nanofluids will decrease. This is consistent in the study done by few researchers on the

effect of temperature on viscosity of nanofluids.

2.4.3 Effects of Particle Size on Viscosity of Nanofluids

Nanoparticles come in many sizes. Therefore studies on effect of particle size on

viscosity of nanofluids are done by some researcher. The results show different kind of

trend.

Nguyen et al. [44] have conducted an experiment on effect of aluminum oxide size

on the viscosity of the nanofluids formed using water as base fluids. In their experiment,

aluminum oxide with 36 nm and 47 nm and volume fraction of 4% are used. They found

that viscosity of nanofluids using 36 nm aluminum oxide nanoparticles is lower by 5% than

one with size of 47 nm. As volume fraction increase, the viscosity difference is greater.

Therefore they have concluded that as particle sizes increase, viscosity of nanofluids also

increases.

He et al. [45] also have conducted an experiment to determine that particle size

have on nanofluids viscosity. In his experiment, titanium oxide with the size of 95 nm, 145

nm and 210 nm are used as nanoparticles and water is used as base fluids. They have found

that as the nanoparticle size increase, the nanofluids viscosities also increase. Their findings

is consistent with the studies done by Nguyen et al. [44].

24

On contrary, Lu and Fan [46] found that viscosity decreases as particle size increase

during their experiment. They use aluminum oxide as nanoparticles in addition to water and

ethylene glycol as the base fluids. Besides that, they also discovered that for nanoparticles

with the size more than 30 nm, the change in shear viscosity is very small.

Anoop et al. [42] also have the same result as Lu and Fan [46] during their

experiment. They use 45 nm as well as 150 nm of aluminum oxide as nanoparticles and

water as base fluid. In the experiment, they observed that the viscosity is lower for the

sample using 150 nm of aluminum oxide than the viscosity using 45 nm of aluminum oxide

at all 2%, 4%, and 6% volume fraction.

Therefore more research needs to be done in order to understand the behavior of the

effect of particle sizes on the viscosities of nanofluids as researchers experimental results

have shown contradiction between them.

2.5 pH of Nanofluids

Currently, there is very little research done on the pH of nanofluids. pH of

nanofluids is an important properties since it affects the stability of nanofluids. There is

very little research done on effect of pH on nanofluids.

Yousefi et al. [47] has done a research using multi walled carbon nanotubes

(MWCNT) as nanoparticles and water as base fluids. In their research, they use Triton X as

additive to regulate pH of nanofluids to 3.5, 6.5 and 9.5. They found that a nanofluid is

most stable at pH 3.5 followed by 6.5 and lastly is 9.5. The author suggest that this

phenomenon happens because as solution become more acidic, there will be higher charges

at nanofluids surface which helps reducing the nanoparticles aggregation hence producing a

more stable nanofluids.

25

There is also a study done by Murshed et al. [48] on effect of pH in nanofluids

stability. In their experiment, they used titanium oxide as nanoparticles and water as base

fluids. The experiment is conducted by using pH 3.4 and pH 9. They found that the thermal

conductivity decrease by 2% at pH 9. Therefore they conclude that pH have very small

effect on nanofluid.

Wang et al. [49] also has conducted an experiment on finding optimum pH for

nanofluids combination of copper as nanoparticles and water as base fluid also aluminum

oxide as nanoparticles and water as base fluids. In their research, they found that the

optimum pH for combination of copper and water nanofluids is 9.5 whereas optimum pH

for combination of aluminum oxide and water nanofluids is 8.

The findings show that different combinations of nanofluids have different optimum

pH. Therefore more studies should be done on effect of pH on nanofluids because there are

so many contradictions in researchers’ findings.

2.6 Conclusion

From literature study, the findings of previous researchers on thermal conductivity,

viscosity and pH of nanofluids are studied and summarize. Besides that, it can be seen that

very little studies are done using silver oxide nanoparticles and almost no study are being

done using sodium chloride solution as base fluid. Therefore in this research, silver oxide is

chosen as nanoparticles and sodium chloride is chosen as the base fluids. In addition, there

are very little research done on viscosity and pH of nanofluids. Therefore study on

viscosity and pH are done on nanofluids as they play an important role in enhancing the

thermal conductivity of nanofluids.

26

Chapter 3

METHODOLOGY

3.1 Overview

In this project, proper methodology is required to complete this project in order.

Therefore the first phase of this research project is the planning phase to make sure this

research moves in orderly manner. Secondly it will move to the experiment phase where

the experiment is conducted after a proper plan has been done. After experiment has been

done, the research moves to the analysis phase where results are sorted and analyzed

properly.

3.2 Methodology

3.2.1 Planning Phase

Planning phase is the most important phase of in this research project because

without a proper planning, this research will not be able to be completed within the time

given. First step in this phase is to determine the objectives of this research. The objective

of the research is stated in the Chapter 1 of the report. After determining the objective,

basic knowledge to conduct the research and analyzing the results are obtained by doing

some literature reading which are documented in Chapter 2. After knowing the objectives

and knowledge on how to conduct the research, the experiment will moves to the

experiment before finally going to the analysis phase which will be explained in the next

phase.

27

3.2.2 Experiment Phase

In experiment phase, there will be three steps to be done. First is the set-up phase

where all the instruments needed to be used in the experiment are tested and calibrated to

get as little error as possible. This will be explained in Chapter 4 of the report. After going

through set-up phase, the experiment will move to the sample preparation phase where

nanoparticles and base fluids are prepared before experiment is conducted. This will be

explained in Chapter 5 of the report. Finally after experiment is conducted, all the data are

collected using the instrument that has been calibrated which are explained in Chapter 4 of

the report.

3.2.3 Data Analysis

In this phase of methodology, all the data obtained from experiment is recorded and

tabulated in excel. The data of thermal conductivity of nanofluids, viscosity of nanofluids,

and also pH of nanofluids using 0.05% volume fraction, 0.1% volume fraction, 0.2%

volume fraction, 0.3% volume fraction and 0.5% volume fraction at temperature in the

range of 30 to 80 degree celcius are analyzed and graphs of them are generated. The graph

that compares the effect of temperature and volume fraction on thermal conductivity,

viscosity and pH are presented and discussed as well. These will all be placed in Chapter 6

of the research. Besides that, the suggestion for further improvement and summary of this

research will be explained in Chapter 7.

28

Chapter 4

EXPERIMENTAL SET-UP

4.1 Overview

In this chapter, the setup of experiment will be explained. There are three type of

setup needs to be done which are used to conduct this experiment which are nanofluids

setup, sonication setup and measuring equipment setup.

4.2 Nanofluid

In this experiment, base fluid used is sodium chloride with molarity of 1 mol.

Therefore to form sodium chloride solution, an amount of sodium chloride are used and

dispersed in a volume of distilled water. As for nanoparticles, silver(I) oxide is used.

4.2.1 Base fluid

SODIUM CHLORIDE

Sodium chloride is obtained from Monash University Sunway Campus Chemical

Laboratory in powder form. This sodium chloride is produced by R & M Chemicals Ltd.

and has an ionic formula of NaCl. It has molar mass of M = 58.44 g/mol. Sodium chloride

is inorganic compound and widely used in food preservation. It is also very soluble in water

with solubility of 359 g/L. Figure 5 shows the sodium chloride used in the experiment.

29

Figure 5 : Sodium chloride

DISTILLED WATER

Distilled water is obtained from Monash University Sunway Campus Chemical

Laboratory. Distilled water is water that is produced by distillation. Distillation is done to

remove impurities in the water and the process of distillation includes boiling of water and

condensing the steam in a clean container. Figure 6 shows the distilled water used in the

experiment

30

Figure 6: Distilled water

MAGNETIC STIRRER

Magnetic stirrer used in this experiment is bought by Monash University Sunway

Campus Chemical Laboratory. It is made by Heidolph Instrument. The model of the stirrer

used is MR Hei Standard. The purpose of using magnetic stirrer is to make sure the sodium

chloride is totally dispersed in distilled water and homogeneous. Besides that, it is also used

to heat up the base fluid for enhancement calculation as it has heater function as well.

Figure 7 shows the magnetic stirrer used in the experiment.

Figure 7: Magnetic Stirrer

31

PARAFILM

Parafilm used in this experiment is obtained from the Monash University Sunway

Campus Chemical Laboratory. It is made by Pechiney Plastic Packaging Company.

Parafilm is a plastic paraffin film and known for its ductility, malleability, odourless and

cohesive behaviour. In this experiment, parafilm is used to cover beaker of the base fluid

prepare in order to avoid any dust from entering the fluid not used. Figure 8 shows the

parafilm used in this experiment.

Figure 8 : Parafilm

ALUMINUM FOIL

Aluminum foil is obtained from Monash University Sunway Campus Mechanical

Laboratory. The aluminum foild used is made by Diamond. Aluminum foil is a thin

aluminum metal that is prepared with thickness as small as 0.2 mm. Aluminum foil is used

to cover the nanofluids during sonication to prevent the evaporation of base fluids to the

surrounding. Aluminum foil instead of parafilm because parafilm tends to deform at high

32

temperature while aluminum foil does not. Figure 9 shows the aluminum foil used in the

experiment and figure 10 shows the nanofluids covered with aluminum foil.

Figure 9 : Aluminium foil

Figure 10 : Nanofluids covered with aluminium foil before sonication

33

4.2.2 Nanoparticle

Nanoparticles used in this experiment is silver(I) oxide. Silver(I) oxide has the

molecular formula of Ag2O. It is obtained from Sigma-Aldrich with product number of

85260 in powder form. It has the particle size of about 60 nm. The density of silver oxide

used is 7.143 g/cm3

and the molecular mass is 231.735 g/mol. Nanoparticles used are

shown in figure 11 and figure 12.

Figure 11 : Silver(I) oxide nanoparticles in the bottle

Figure 12 : Silver(I) oxide nanoparticles in powder form

34

4.3 Sonication

Sonication is the process where nanofluids are synthesis. This is the part where

nanoparticles will be dispersed in the base fluid using sonication process. Therefore before

experiment is conducted, there are few setups need to be done. First is the setting of

ultrasonic processor, followed by sound enclosure setting and ultrasonic probe.

4.3.1 Ultrasonic Processor

Ultrasonic processor is used in the preparation of nanofluid in two-step method.

Sonication has the role of dispersing silver(I) oxide in sodium chloride solution to form

silver nanofluids. The ultrasonic processor used in this experiment is made by Qsonica with

the model of Q 700. This sonicator specification for power is 700 watts and frequency is 20

kHz and voltage of 110V at 60 kHz. The amplitude in this experiment is set at 20 because

according to the instruments manual, it is safe amplitude in sonication of liquid less than

250mL. In this experiment, the amount of liquid used is 120 ml. The sonication process is

set to be 5 hours and shutdown temperature is set to be 90 degree celcius. The pulse on

time is 3 seconds and pulse off time is 1 seconds.

Based on operator`s manual, the ultrasonic electric generator will converts the

alternative current power to a 20kHz signal. The transducer then will be the signal to a

mechanical vibration which then are amplified and transmitted to the nanoparticles and

base fluid mixture by the longitudinal expansion and contraction of ultrasonic probe. The

constant vibration will create a pressure waves in the sample. As the amount of vibration

increase, microscopic bubbles are formed in the sample. These microscopic bubbles will

implode creating shock waves and increase the sample`s temperature. This is known as

cavitation. Although the effect is minimal, as thousands of cavitation happens, high energy

is released in the cavitation field. Figure 13 shows the ultrasonic processor used in the

experiment and figure 14 show the settings done for the sonication process.

35

Figure 13: Ultrasonic Processor with probe

Figure 14: Ultrasonic processor sonication setting.

36

4.3.2 Ultrasonic Probe

In this experiment, the ultrasonic probe used has the model number of CL-334.

Probe has diameter of 0.5 inch which provide high intensity sonication. According to the

manufacturer, probe with diameter 0.5 inch are recommended for small samples ranging

from 10 to 250 mL samples. Larger samples will requires larger probe diameter because the

small diameter may not be able to disperse the large sample completely. In this experiment

0.5 inch as probe diameter is enough as the sample used has the volume of only 120 mL.

There are two methods to use ultrasonic probe which are direct sonication and indirect

sonication.

Direct sonication is done by inserting the probe directly into the sample and let

sonication process starts. This is used in this experiment. Probes can are made from

titanium. Indirect sonication on the other hand is done by inserting the probe in a tube and

the tube will transmit the ultrasonic energy to the water. This method is used if the sample

size is very small as this eliminates the probability of sample loss by evaporation. Figure 15

shows the probe used in the experiment.

Figure 15 : Ultrasonic probe

37

4.3.3 Sound Enclosure

Sonication is a very noisy process. Therefore sonication process is done in a sound

enclosure where probes are inserted there. The inside of sound enclosure is covered with

polystyrene. According to manufacturer’s manual, sound enclosure can reduce the noise by

almost 20 dBa.

Besides that, the enclosure also contains an internal support rod as well as converter

mounting system which will hold the probe tightly inside the enclosure. There is a window

in front of the enclosure to monitor the sonication process. In addition, sonication process

produces waves which will attract dust from surrounding. Therefore this enclosure can

reduce the probability of dust entering the sample during sonication process. Figure 16

shows the sound enclosure used in the experiment.

Figure 16: Sound Enclosure

Sound Enclosure

38

4.4 Measuring apparatus

Measuring apparatus used in this experiment are weighing machine which is used to

prepare nanoparticles and base fluids, thermal conductivity analyzer which is used to

measure thermal conductivity, vibro viscometer which is used to measure viscosity and

finally pH meter which is to measure the pH of the nanofluids. Conical-bottom centrifuge

tubes on the other hand are used to store the fluid to take the thermal conductivity reading.

4.4.1 Weighing Machine

Weighing machine used is obtained from Monash University Sunway Campus

Mechanical lab. The weighing machine used is made by A & D Instruments Ltd. and the

model of the weighing machine used is FX- 3000i series. This machine has the accuracy of

± 0.002g. This weighing machine is used to measure the weight of nanoparticles and

sodium chloride. Parafilm is place on the weighing machine and re-zero before

nanoparticles and sodium chloride is placed on them to make sure the correct weight are

used in the experiment. Figure 17 shows the weighing machine used in the experiment to

measure the weight of nanoparticles and sodium chloride.

Figure 17 : Weighing machine Fx-3000i

39

4.4.2 Thermal Conductivity Analyzer

Thermal conductivity analyzer used in this experiment is obtained from Monash

University Sunway Campus Mechanical Laboratory. It is made by Decagon devices, Inc.

and the model is called KD2 Pro. A small needle with KS-1 sensor is used to measure the

thermal conductivity of the nanofluids for 60 seconds and the value will be displayed at

KD2 Pro displaying device. KD2 Pro has the accuracy of ± 5%.

KD2 Pro is constructed with the working principle of hot wire method. According

to manual given by operator, there are two temperature response equations to explain how

KD2 Pro works. First is the when 0 < t ≤ t1

(

) (4.1)

After the heating is off, for t > t1 , the temperature change equation is defined as:

(

) (

( ) ) (4.2)

where,

= rate of heat dissipation

k = thermal conductivity of the medium

Ei = exponential integral

r = radial distance from heating source

t = time

t1 = heating time

α = thermal diffusivity

40

The thermal properties of material and thermal diffusivity are determined by fitting

the time series for heating in equation 1 and for cooling in equation by using non-linear

square method which is explained in the literature given by the operator. KD2 Pro also will

display the error during measurement and according to the manual error of 0.01 or less will

give the accurate reading of thermal conductivity. Figure 18 shows the KD2 Pro used in the

experiment and figure 19 show the KS-1 sensor needle.

Figure 18: KD2 Pro device

Figure 19: KS-1 sensor needle

41

4.4.3 Vibro Viscometer

Vibro viscometer used is provided by Monash University Sunway Campus

Mechanical Laboratory. It is made by A & D Instrument Ltd. and the model of the

viscometer is SV-10. This viscometer has the accuracy of ± 1%. SV-10 viscometer

measures the viscosity of the fluid by controlling the amplitude of the sensor plate which is

place inside the sample. Electric current will drive the sensor plate to determine the

viscosity. This viscometer can determine the dynamic viscosity of the sample ranging from

0.3 mPa.s to 10 000 mPa.s according to the manual. SV-10 also can determine the

temperature of the samples by having one temperature sensor place in between the two

sensor plates. Changes in temperature and viscosity can be observed clearly from the

viscometer display. Figure 20 shows the vibro viscometer used in the experiment and figure

21 shows the sensor plate and temperature sensor in viscometer.

Figure 20: The SV-10 Vibro Viscometer

42

Figure 21: Sensor plate and temperature sensor

4.4.4 pH meter

pH meter used is provided by Monash University Sunway Campus Mechanical

Laboratory. It is made by Sartorius Company with model number of PB-10. This pH meter

has measuring accuracy of ± 1% in pH reading and ± 0.2 degree celcius in temperature

reading. pH meter has an electrode which is integrated with temperature sensor to measure

the pH and temperature of sensor. The electrode are placed inside the sample and pH of the

sample will be displayed on pH meter. PB-10 pH meter can measure a range of pH from 0

to 14 and temperature in the range of -5 to 105 degree celcius according to operator`s

manual. Figure 22 shows the pH meter used in the experiment.

Sensor

plate

Temperature

sensor

43

Figure 22: PB-10 Standard pH meter.

4.7 Conical-bottom centrifuge tubes

Conical-bottom centrifuge tubes are supplied by Monash University Sunway

Campus Mechanical Laboratory. It has 50mL capacity and used to store nanofluids in order

to take thermal conductivity data. The tubes can withstand temperature in the range of -40

to 80 degree celcius. Figure 23 shows the conical centrifuge tube used in the experiment.

Figure 23: Conical-bottom centrifuge tube

44

Chapter 5

EXPERIMENTAL PROCEDURES

5.1 Overview

In this experiment, there are three major processes in completing this experiment.

Firstly is the sample preparation process. Then after sample are prepared, it will go through

sonication process and finally the data collecting process.

5.2 Sample preparation

There are two samples needs to be prepared which are the sodium chloride base

fluids and silver oxide with volume fraction of 0.05%, 0.1%, 0.2%, 0.3% and 0.5%.

5.2.1 Base fluids preparation procedure

1. One litres of one mol sodium chloride (NaCl) solution are prepared;

i) Molar mass of NaCl = 58.44 g/mol

ii) Molarity of NaCl = 1 mol

( ) (5.1)

Weight of NaCl = 58.44 g/mol x 1 mol

= 58.44 g

2. Weight 58.44 g of NaCl powder on FX-3000i weighing machine

3. Place the NaCl powder in a 1 litres beaker

4. Add distilled water until it reaches 1 litres

5. Place the 1 litres beaker on a magnetic stirrer for 2 minutes to make the solution

homogenous

6. Pour 120 ml of sodium chloride in a 150 ml beaker

45

5.2.2 Nanoparticles preparation procedure

1. Amount of nanoparticles needed are calculated for volume fraction.

a. Volume concentration (φ = Vnanoparticles / Vbase fluids x 100)

b. φ = 0.05%

c. V basefluid = 120 mL

d. Density of Al2O, = 7.143 g/mL

Mass nanoparticles is calculated using,

2. Weight 0.428 g of silver oxide on Fx-3000i weighing machine

3. Place the nanoparticles inside the 120mL sodium chloride

4. Step 1 until 3 is repeated for sample preparation of 0.1%, 0.2%, 0.3% and 0.5%

volume fraction. Calculations of mass of others are in Appendices.

Table 2: Mass of silver oxide for different volume fraction

Volume Fraction (%) Mass of Nanoparticles (g)

0.05 0.428

0.1 0.856

0.2 1.712

0.3 2.568

0.5 4.280

46

Figure 24 : Nanoparticles in base fluids prepared

5.3 Sonication Process

After nanoparticles are placed in base fluids, the beaker is covered with aluminum

foil. This is to prevent dust from entering the nanofluids during sonication process and also

to prevent the evaporation of nanofluids. The beaker is then placed in the sound enclosure

and ultrasonic probe are placed in the middle of total volume of the beaker. This is to

prevent the probe from touching the wall of beaker incase the beaker moves during

sonication process. Besides that, placing the probe in the middle of the total volume also

makes the efficiency of sonication higher as all nanoparticles are being covered during the

process. After that sonication process will start. Sonication process is chosen as it can

reduce the aggregation during nanofluids synthesis. The sonicator is set to run for 5 hours

with 3 seconds pulse on and 1 second pulse off. This is to prevent the sonicator from

overheating and breakdown. After sonication process is done, nanofluids are formed and

data are ready to be collected. Data are collected 5 times in the range of 30 degree celcius

to 80 degree celcius. As for base fluid, it is heated until 80 degrees using Heidolph MR Hei

Standard and thermal conductivity and viscosity are taken so at temperature difference of ±

1 degree celcius of the data taken for nanofluids for enhancement calculation.

47

Figure 25 : Ultrasonic probe tip at the centre of nanofluid

Figure 26 : Sonication process

Figure 27 : 5 hours sonication time

48

5.4 Data collection

In this experiment, three thermo-properties of nanoparticles are taken. Firstly

thermal conductivity of nanofluids is taken using KD2Pro. Five data are taken in the range

of 30 to 80 degree celcius. Then viscosity of nanofluids is taken using SV-10 Vibro

Viscometer. Five data are taken as well in the range of 30 to 60 degree celcius. Finally PB-

10 pH meter is used to measure the pH of nanofluids. Five data again are taken in the range

of 30 to 70 degree celcius.

5.4.1 KD2 Pro

KD2 Pro is used to measure the thermal conductivity in this experiment. Before

thermal conductivity of the nanofluids is taken, calibration of KD2 Pro and KS-1 sensor are

conducted using KD2 Pro Verification Standard Glycerin. KD2 Pro Verification Standard

Glycerin has thermal conductivity of 0.285 W/m.K. Five measurement are taken during

calibration and the results is as follow.

Table 3: Calibration using KD2 Pro Verification Standard Glycerin

Temperature (⁰C) Thermal Conductivity (W/ m.K) Error

24.59 0.282 0.0083

24.78 0.285 0.0038

25.03 0.283 0.0074

24.97 0.282 0.0086

24.69 0.283 0.0077

The results shows error which is less than 0.01 hence the measurement is almost accurate.

In this experiment, nanofluids formed are placed in conical-bottom centrifuge tube

for data collection. The KS-1 sensor needle is place in the middle of the tube and hold for

60 seconds to get accurate data. Movement of needle can affect the accuracy of data

acquired. Besides that of KS-1 sensor needle also needs to be straight as bended sensor will

affect accuracy of data acquired as well.

49

Figure 28: KD2 Pro Verification Standard Glycerin

Figure 29: KS-1 sensor needle placed at the centre of the base fluid

50

5.4.2 SV-10 Vibro Viscometer

SV-10 Vibro Viscometer is used to measure the viscosity of nanofluid. Before

viscosity of nanofluids are taken, viscosity of distilled water at are tested using vibro

viscometer observe the accuracy of the viscometer. According to operator`s manual,

distilled water can be used to test the accuracy of the viscometer. Therefore five data are

taken using distilled water. It is known that distilled water has a viscosity of 1.05 mPa.s at

25 degree celcius. The result of testing is as follow:

Table 4: Calibration using distilled water

Temperature (⁰C) Viscosity (mPa.s)

24.9 1.05

25.0 1.04

24.9 1.05

25.1 1.04

25.0 1.05

The data taken only have differences of 0.01 mPa.s between them which show that the

device is working properly.

When taking readings, sample is poured until 35 mL or 45 mL mark. Besides that,

for accurate reading, half of the thin bended side of the sensor is immersed into the

samples. Avoid vibration when taking reading as it can reduce the accuracy of the result

taken. If possible, use a vibration free table when taking reading.

51

Figure 30: Correct set up to take viscosity data

5.2.3 PB-10 pH meter

PB-10 pH meter is used to measure the pH of nanofluids. Before measurements are

taken, the pH meter is calibrated using pH buffer solution. Five data are taken using pH 7

buffer solutions.

Table 5: Calibration using pH buffer solution of 7

Temperature (⁰C) pH level

25.1 7.00

24.9 7.01

25.0 7.00

24.9 7.00

25.1 6.99

The data obtain from calibration of pH meter shows difference of only 0.01 in pH reading

and 0.01 for temperature reading. This shows that pH meter is working properly.

In this experiment, electrode of pH meter must be fully immersed in the liquid

sample in order to obtain accurate results. Besides that, the data must be taken on a

vibration free table as vibration will reduce the accuracy of data collected.

52

Figure 31: Picture above shows pH Buffer Solution.

Figure 32: pH Electrode fully immersed in base fluid.

5.5 Sonication time

In this experiment, sonication time is chosen to be 5 hours. This is because

experiment when using 3 hours and 4 hours sonication time gives very fluctuating data on

thermal conductivity and also pH. Besides that, the viscosity difference also is huge. This is

because of agglomeration of samples and stability of nanoparticles affected the results. At 5

hours sonication time, the data of thermal conductivity, viscosity and pH is more stable.

The graph that compares the differences of data obtained for thermal conductivity

sonication time of 3, 4 and 5 hours for 0.05% volume fraction is presented in Appendices.

53

Chapter 6

RESULTS AND DISCUSSION

6.1 Overview

In this chapter, the results obtained from the experiments done will be presented in

graphs. Every finding on thermal conductivity, viscosity and pH of Ag2O-NaCl nanofluids

in every volume fraction of 0.05%, 0.1%, 0.2%, 0.3%, and 0.5% will be analyzed and

comparison of the difference between volume fraction and temperature will be discussed

thoroughly.

6.2 Results

In this part, the findings of thermal conductivity, viscosity and pH of Ag2O-NaCl

nanofluids with volume fraction 0.05%, 0.1%, 0.2%, 0.3% and 0.5% are presented in

graph.

6.2.1 Volume fraction of 0.05% Ag2O-NaCl nanofluid

This section will be divided into three parts which are thermal conductivity,

viscosity and pH of nanofluids. As mentioned in section 5.2.2, amount of silver(I) oxide

used in this section is 0.428 g and 120 mL of sodium chloride solution forming 0.05%

Ag2O-NaCl nanofluid.

54

THERMAL CONDUCTIVITY

Thermal conductivity is the ability of an object or substance in conducting heat. It is

measured in watts per meter kelvin ( W/m.K ). The graph of thermal conductivity against

temperature for 0.05% volume fraction of Ag2O-NaCl nanofluid is presented in figure 33;

Figure 33: Effect of temperature on thermal conductivity of 0.05% volume fraction of

Ag2O-NaCl nanofluid

From figure 33, it can be see that the as temperature of Ag2O-NaCl nanofluid

increase, thermal conductivity also increases. This is consistent with the study done in

literature review in section 2.3.2. The highest thermal conductivity achieved for volume

fraction of 0.05% is at temperature 74.4 degree celcius with the value of 0.713 W/m.K.

0.65

0.66

0.67

0.68

0.69

0.7

0.71

0.72

30 40 50 60 70 80

The

rmal

Co

nd

uct

ivit

y (W

/m.K

)

Temperature (Celcius)

Thermal Conductivity vs Temperature of 0.05% volume fraction of Ag2O-NaCl nanofluid

0.05% volume fraction

Linear (0.05% volumefraction)

55

VISCOSITY

Viscosity is a measurement of fluids resistivity from undergoing deformation under

shear stress or tensile stress. Viscosity also can be defined as molecular attraction between

molecules inside fluids. Viscosity has the unit of mPa.s. The graph of viscosity against

temperature for 0.05% volume fraction of Ag2O-NaCl nanofluid is presented in figure 34;

Figure 34: Effect of temperature on viscosity of 0.05% volume fraction of Ag2O-NaCl

nanofluid

From figure 34, it can be see that the as temperature of Ag2O-NaCl nanofluid

increase, viscosity decreases. This is consistent with the study done in literature review in

section 2.4.2. The lowest thermal viscosity achieved for volume fraction of 0.05% is at

temperature 60.2 degree celcius with the value of 0.54 mPa.s.

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

30 40 50 60 70

Vis

cosi

ty (

mP

a.s)

Temperature (Celcius)

Viscosity vs Temperature of 0.05% volume fraction of Ag2O-NaCl nanofluid

0.05% volume fraction

Linear (0.05% volumefraction)

56

PH

In nanofluids, pH is used to determine the state of nanofluids. pH are measured in

the range of 1 until 14. The graph of pH against temperature for 0.05% volume fraction of

Ag2O-NaCl nanofluid is presented in figure 35;

Figure 35: Effect of temperature on pH of 0.05% volume fraction of Ag2O-NaCl nanofluid

From the graph, the highest pH is at temperature 60.3 degree celcius with pH of

7.19 and the lowest pH is at temperature 32.9 with pH of 7.11. Nanofluid is neutral.

6.2.2 Volume fraction of 0.1% Ag2O-NaCl nanofluid

This section will be divided into three parts which are thermal conductivity,

viscosity and pH of nanofluids. As mentioned in section 5.2.2, amount of silver(I) oxide

used in this section is 0.856 g and 120 mL of sodium chloride solution forming 0.1%

Ag2O-NaCl nanofluid.

7.1

7.11

7.12

7.13

7.14

7.15

7.16

7.17

7.18

7.19

7.2

30 40 50 60 70

pH

Temperature (Celcius)

pH vs vs Temperature of 0.05% volume fraction of silver nanofluids

0.05% volume fraction

Linear (0.05% volumefraction)

57

THERMAL CONDUCTIVITY

Thermal conductivity is the ability of an object or substance in conducting heat. It is

measured in watts per meter kelvin ( W/m.K ). The graph of thermal conductivity against

temperature for 0.1% volume fraction of Ag2O-NaCl nanofluid is presented in figure 36;

Figure 36: Effect of temperature on thermal conductivity of 0.1% volume fraction of Ag2O-

NaCl nanofluid

From figure 33, it can be see that the as temperature of Ag2O-NaCl nanofluid

increase, thermal conductivity also increases. This is consistent with the study done in

literature review in section 2.3.2. The highest thermal conductivity achieved for volume

fraction of 0.1% is at temperature 73.2 degree celcius with the value of 0.91 W/m.K.

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

30 40 50 60 70 80

The

rmal

Co

nd

uct

ivit

y (W

/m.K

)

Temperature (Celcius)

Thermal Conductivity vs Temperature of 0.1% volume fraction of Ag2O-NaCl nanofluid

0.1% volume fraction

Linear (0.1% volume fraction)

58

VISCOSITY

Viscosity is a measurement of fluids resistivity from undergoing deformation under

shear stress or tensile stress. Viscosity also can be defined as molecular attraction between

molecules inside fluids. Viscosity has the unit of mPa.s. The graph of viscosity against

temperature for 0.1% volume fraction of Ag2O-NaCl nanofluid is presented in figure 37;

Figure 37: Effect of temperature on viscosity of 0.1% volume fraction of Ag2O-NaCl

nanofluid

From figure 34, it can be see that the as temperature of Ag2O-NaCl nanofluid

increase, viscosity decreases. This is consistent with the study done in literature review in

section 2.4.2. The lowest thermal viscosity achieved for volume fraction of 0.1% is at

temperature 61.3 degree celcius with the value of 0.56 mPa.s.

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

30 40 50 60 70

Vis

cosi

ty (

mP

a.s)

Temperature (Celcius)

Viscosity vs Temperature of 0.1% volume fraction of Ag2O-NaCl nanofluid

0.1% volume fraction

Linear (0.1% volume fraction)

59

PH

In nanofluids, pH is used to determine the state of nanofluids. pH are measured in

the range of 1 until 14. The graph of pH against temperature for 0.1% volume fraction of

Ag2O-NaCl nanofluid is presented in figure 38;

Figure 38: Effect of temperature on pH of 0.1% volume fraction of Ag2O-NaCl nanofluid

From the graph, the highest pH is at temperature 60.2 degree celcius with pH of

7.18 and the lowest pH is at temperature 33.1 with pH of 7.08. Nanofluid is neutral.

6.2.3 Volume fraction of 0.2% Ag2O-NaCl nanofluid

This section will be divided into three parts which are thermal conductivity,

viscosity and pH of nanofluids. As mentioned in section 5.2.2, amount of silver(I) oxide

used in this section is 1.712 g and 120 mL of sodium chloride solution forming 0.2%

Ag2O-NaCl nanofluid.

7.06

7.08

7.1

7.12

7.14

7.16

7.18

7.2

30 40 50 60 70

pH

Temperature (Celcius)

pH vs vs Temperature of 0.1% volume fraction of Ag2O-NaCl nanofluid

0.1% volume fraction

Linear (0.1% volumefraction)

60

THERMAL CONDUCTIVITY

Thermal conductivity is the ability of an object or substance in conducting heat. It is

measured in watts per meter kelvin ( W/m.K ). The graph of thermal conductivity against

temperature for 0.2% volume fraction of Ag2O-NaCl nanofluid is presented in figure 39;

Figure 39: Effect of temperature on thermal conductivity of 0.2% volume fraction of Ag2O-

NaCl nanofluid

From figure 33, it can be see that the as temperature of Ag2O-NaCl nanofluid

increase, thermal conductivity also increases. This is consistent with the study done in

literature review in section 2.3.2. The highest thermal conductivity achieved for volume

fraction of 0.2% is at temperature 73.42 degree celcius with the value of 1.473 W/m.K.

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

30 40 50 60 70 80

The

rmal

Co

nd

uct

ivit

y (W

/m.K

)

Temperature(Celcius)

Thermal Conductivity vs Temperature of 0.2% volume fraction of Ag2O-NaCl nanofluid

0.2% volume fraction

Linear (0.2% volumefraction)

61

VISCOSITY

Viscosity is a measurement of fluids resistivity from undergoing deformation under

shear stress or tensile stress. Viscosity also can be defined as molecular attraction between

molecules inside fluids. Viscosity has the unit of mPa.s. The graph of viscosity against

temperature for 0.2% volume fraction of Ag2O-NaCl nanofluid is presented in figure 40;

Figure 40: Effect of temperature on viscosity of 0.2% volume fraction of Ag2O-NaCl

nanofluid

From figure 34, it can be see that the as temperature of Ag2O-NaCl nanofluid

increase, viscosity decreases. This is consistent with the study done in literature review in

section 2.4.2. The lowest thermal viscosity achieved for volume fraction of 0.2% is at

temperature 60.8 degree celcius with the value of 0.6 mPa.s.

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

30 40 50 60 70

Vis

cosi

ty (

mP

a.s)

Temperature(Celcius)

Viscosity vs Temperature of 0.2% volume fraction of Ag2O-NaCl nanofluid

0.2% volume fraction

Linear (0.2% volume fraction)

62

PH

In nanofluids, pH is used to determine the state of nanofluids. pH are measured in

the range of 1 until 14. The graph of pH against temperature for 0.2% volume fraction of

Ag2O-NaCl nanofluid is presented in figure 41;

Figure 41: Effect of temperature on pH of 0.2% volume fraction of Ag2O-NaCl nanofluid

From the graph, the highest pH is at temperature 60.2 degree celcius with pH of

7.14 and the lowest pH is at temperature 32.8 with pH of 7.03. Nanofluid is neutral.

6.2.4 Volume fraction of 0.3% Ag2O-NaCl nanofluid

This section will be divided into three parts which are thermal conductivity,

viscosity and pH of nanofluids. As mentioned in section 5.2.2, amount of silver(I) oxide

used in this section is 2.568 g and 120 mL of sodium chloride solution forming 0.3%

Ag2O-NaCl nanofluid.

7

7.02

7.04

7.06

7.08

7.1

7.12

7.14

7.16

30 40 50 60 70

pH

Temperature(Celcius)

pH vs Temperature of 0.2% volume fraction of Ag2O-NaCl nanofluid

0.2% volume fraction

Linear (0.2% volumefraction)

63

THERMAL CONDUCTIVITY

Thermal conductivity is the ability of an object or substance in conducting heat. It is

measured in watts per meter kelvin ( W/m.K ). The graph of thermal conductivity against

temperature for 0.3% volume fraction of Ag2O-NaCl nanofluid is presented in figure 42;

Figure 42: Effect of temperature on thermal conductivity of 0.3% volume fraction of Ag2O-

NaCl nanofluid

From figure 33, it can be see that the as temperature of Ag2O-NaCl nanofluid

increase, thermal conductivity also increases. This is consistent with the study done in

literature review in section 2.3.2. The highest thermal conductivity achieved for volume

fraction of 0.3% is at temperature 61.8 degree celcius with the value of 1.712 W/m.K.

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

30 40 50 60 70 80

The

rmal

Co

nd

uct

ivit

y (W

/m.K

)

Temperature(Celcius)

Thermal Conductivity vs Temperature of 0.3% volume fraction ofAg2O-NaCl nanofluid

0.3% volume fraction

Linear (0.3% volume fraction)

64

VISCOSITY

Viscosity is a measurement of fluids resistivity from undergoing deformation under

shear stress or tensile stress. Viscosity also can be defined as molecular attraction between

molecules inside fluids. Viscosity has the unit of mPa.s. The graph of viscosity against

temperature for 0.3% volume fraction of Ag2O-NaCl nanofluid is presented in figure 43;

Figure 43: Effect of temperature on viscosity of 0.3% volume fraction of Ag2O-NaCl

nanofluid

From figure 34, it can be see that the as temperature of Ag2O-NaCl nanofluid

increase, viscosity decreases. This is consistent with the study done in literature review in

section 2.4.2. The lowest thermal viscosity achieved for volume fraction of 0.3% is at

temperature 53.8 degree celcius with the value of 0.7 mPa.s.

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

30 35 40 45 50 55 60

Vis

cosi

ty (

mP

a.s)

Temperature(Celcius)

Viscosity vs Temperature of 0.3% volume fraction of Ag2O-NaCl nanofluid

0.3% volume fraction

Linear (0.3% volume fraction)

65

PH

In nanofluids, pH is used to determine the state of nanofluids. pH are measured in

the range of 1 until 14. The graph of pH against temperature for 0.3% volume fraction of

Ag2O-NaCl nanofluid is presented in figure 44;

Figure 44: Effect of temperature on pH of 0.3% volume fraction of Ag2O-NaCl nanofluid

From the graph, the highest pH is at temperature 54.2 degree celcius with pH of

7.13 and the lowest pH is at temperature 30.4 with pH of 7.01. Nanofluid is neutral.

6.2.5 Volume fraction of 0.5% Ag2O-NaCl nanofluid

This section will be divided into three parts which are thermal conductivity,

viscosity and pH of nanofluids. As mentioned in section 5.2.2, amount of silver(I) oxide

used in this section is 4.28 g and 120 mL of sodium chloride solution forming 0.05%

Ag2O-NaCl nanofluid.

7

7.02

7.04

7.06

7.08

7.1

7.12

7.14

30 40 50 60 70

pH

Temperature(Celcius)

pH vs Temperature of 0.3% volume fraction of Ag2O-NaCl nanofluid

0.3% volume fraction

Linear (0.3% volumefraction)

66

THERMAL CONDUCTIVITY

Thermal conductivity is the ability of an object or substance in conducting heat. It is

measured in watts per meter kelvin ( W/m.K ). The graph of thermal conductivity against

temperature for 0.5% volume fraction of Ag2O-NaCl nanofluid is presented in figure 45;

Figure 45: Effect of temperature on thermal conductivity of 0.5% volume fraction of Ag2O-

NaCl nanofluid

From figure 33, it can be see that the as temperature of Ag2O-NaCl nanofluid

increase, thermal conductivity also increases. This is consistent with the study done in

literature review in section 2.3.2. The highest thermal conductivity achieved for volume

fraction of 0.5% is at temperature 61.13 degree celcius with the value of 1.83 W/m.K.

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

30 40 50 60 70 80

The

rmal

Co

nd

uct

ivit

y (W

/m.K

)

Temperature(Celcius)

Thermal Conductivity vs Temperature of 0.5% volume fraction of Ag2O-NaCl nanofluid

0.5% volume fraction

Linear (0.5% volume fraction)

67

VISCOSITY

Viscosity is a measurement of fluids resistivity from undergoing deformation under

shear stress or tensile stress. Viscosity also can be defined as molecular attraction between

molecules inside fluids. Viscosity has the unit of mPa.s. The graph of viscosity against

temperature for 0.5% volume fraction of Ag2O-NaCl nanofluid is presented in figure 46;

Figure 46: Effect of temperature on viscosity of 0.5% volume fraction of Ag2O-NaCl

nanofluid

From figure 34, it can be see that the as temperature of Ag2O-NaCl nanofluid

increase, viscosity decreases. This is consistent with the study done in literature review in

section 2.4.2. The lowest thermal viscosity achieved for volume fraction of 0.5% is at

temperature 53.6 degree celcius with the value of 0.74 mPa.s.

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

30 35 40 45 50 55 60

Vis

cosi

ty (

mP

a.s)

Temperature(Celcius)

Viscosity vs Temperature of 0.5% volume fraction of Ag2O-NaCl nanofluid

0.5% volume fraction

Linear (0.5% volume fraction)

68

PH

In nanofluids, pH is used to determine the state of nanofluids. pH are measured in

the range of 1 until 14. The graph of pH against temperature for 0.5% volume fraction of

Ag2O-NaCl nanofluid is presented in figure 47;

Figure 47: Effect of temperature on pH of 0.5% volume fraction of Ag2O-NaCl nanofluid

From the graph, the highest pH is at temperature 55.1 degree celcius with pH of

7.08 and the lowest pH is at temperature 32.4 with pH of 6.99. Nanofluid is neutral.

6.3 Discussion

In discussion part, the effect of volume fractions and temperatures on thermal

conductivity, viscosity and pH are discussed. Enhancement of thermal conductivity and

comparison of viscosity and pH between base fluids with nanofluids are discussed as well.

6.98

7

7.02

7.04

7.06

7.08

7.1

30 35 40 45 50 55 60

pH

Temperature(Celcius)

pH vs Temperature of 0.5% volume fraction of Ag2O-NaCl nanofluid

0.5% volume fraction

Linear (0.5% volumefraction)

69

6.3.1 Effect of volume fraction and temperature on thermal conductivity

Figure 48 : Effect of volume fraction and temperature on thermal conductivity of Ag2O-

NaCl nanofluid

Figure 48 shows the effect of volume fraction and temperature on thermal

conductivity. From the graph, it can be seen that as volume fraction and temperature

increase, thermal conductivity also increases. This can be explained by the Brownian

motion of nanoparticles in nanofluids. Brownian motion as the random movement of

particles that is suspended in fluid which results in their higher movement rate. As known,

nanoparticles are in solid state and move at slower pace at random whereas base fluids

atoms moves at a faster rate. As the fast moving atoms of base fluids collide with the slow

moving particles, the slow moving particles will gain momentum and moves at faster pace.

Therefore as volume fraction increase, the amount of Brownian motion increases. As there

are higher movement of particles, heat is being transferred at higher rate hence giving a

higher thermal conductivity. Increase of temperature on the other hand will excite the

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

30 40 50 60 70 80

Ther

mal

Co

nd

uct

ivit

y (W

/m.K

)

Temperature(Celcius)

Thermal Conductivity vs Temperature

0.05% volume fraction

0.1% volume fraction

0.2% volume fraction

0.3% volume fraction

0.5% volume fraction

Base fluid (NaCl)

70

particles and atoms in nanofluids to move faster. As they moves at faster rate, heat is

transferred at higher rate as well which will result in increase of thermal conductivity.

Besides that, it can be seen that base fluid`s thermal conductivity is taken at many

points whereas for nanofluids it is taken at only 5 points. This is because limitation of

fluids. When dealing with nanofluids, three types of data needs to be recorded which are

thermal conductivity, viscosity and pH and there is very limited amount of nanofluids

available during preparation whereas when taking the data for base fluids, it can be done

separately as sodium chloride solution are prepared in large quantity as it is available in lab.

6.3.2 Enhancement of thermal conductivity

Figure 49 : Enhancement of thermal conductivity

Figure 49 shows that enhancement of Ag2O-NaCl nanofluids thermal conductivity

in relative to thermal conductivity of NaCl at different temperatures. It can be seen that

Ag2O-NaCl nanofluids have an excellent enhancement in thermal conductivity. The highest

0

50

100

150

200

250

30 40 50 60 70 80

Enh

ance

me

nt

(%)

Temperature (celcius)

Enhancement vs Temperature

0.05% volume fraction

0.1% volume fraction

0.2% volume fraction

0.3% volume fraction

0.5% volume fraction

71

enhancement of thermal conductivity occurs at volume fraction of 0.5% and 60.13 degree

celcius with enhancement of as much as 192.3%. This is because the nature of the

nanoparticles itself that have a high capabilities in conducting heat. As known, silver have

the highest thermal conductivity compared to other metals. Therefore, based on the

experiment findings, it can be said that Ag2O-NaCl nanofluids provide a good enhancement

in thermal conductivity.

6.3.3 Effect of volume fraction and temperature on viscosity

Figure 50 : Viscosity of Ag2O-NaCl nanofluid at different volume fraction and temperature

From figure 50, it can be seen that as volume fraction of Ag2O-NaCl nanofluid

increases, viscosity of nanofluids increases as well. This is because viscosity is a measure

of fluid`s resistance to shear stress or tensile stress. The resistance is formed by interactions

between neighboring molecules inside the fluid. As volume fraction increases, more

molecules of silver oxide are added into the nanofluids. This will results in more

0

0.2

0.4

0.6

0.8

1

1.2

0 20 40 60 80

Vis

cosi

ty (

mP

a.s)

Temperature(Celcius)

Viscosity vs Temperature

0.05% volume fraction

0.1% volume fraction

0.2% volume fraction

0.3% volume fraction

0.5% volume fraction

Base fluid (NaCl)

72

interactions between neighboring molecules which then will increase in fluid`s resistance.

This hence increases the viscosity of nanofluids. Besides that, it can be observed that

Ag2O-NaCl nanofluid at all volume fractions have lower viscosity than NaCl base fluid.

This could probably be because of self-lubrication of silver nanoparticles inside sodium

chloride solution which reduces the viscosity of the base fluids. This phenomenon is similar

to the research done by Wang et al. [50] where their graphene nanofluids have lower

viscosity than the base fluid.

As for temperature, it can be observed that as temperature increases, viscosity

decreases. This is because as temperature increase, molecules inside the nanofluids will

gain more energy at moves at a faster rate. Therefore as it moves faster, the attraction

between molecules becomes weaker making the nanofluid resistance lower. This will

reduce the viscosity of nanofluids. Therefore it can be concluded that Ag2O-NaCl nanofluid

exhibit a good low viscosity properties.

6.3.4 Effect of volume fraction and temperature on pH

Figure 51 : pH of nanofluids with different volume fraction at different temperature

6.95

7

7.05

7.1

7.15

7.2

30 40 50 60

pH

Temperature

pH vs Temperatue

0.05% volume fraction

0.1% volume fraction

0.2% volume fraction

0.3% volume fraction

0.5% volume fraction

Base fluid (NaCl)

73

From figure 51, it can be observed that as temperature increase, pH slightly

increases. This can be explained by the existence of halogen molecules in Ag2O-NaCl

nanofluids. When halogen molecules (Cl) are dispersed in water, they will hydrolize and

form hydrohalogen and hypohalogenic acids. Both will dissociate in water. As temperature

increases, some of the halogen molecules (Cl) will evaporates. This will results in less

hypohalogenic acids that dissociate in water. This then will shift equilibrium to the left and

increase the pH.

pH is used to study the stability of nanofluids. As shown in the graph, pH of

nanofluids lies in pH 6.98 to pH 7.2 for all volume fractions. Therefore nanofluids formed

are neutral. Figure 52 shows sedimentation happens to silver nanofluids after five hours

nanofluids has formed. This shows that nanofluids are stable only for four hour. According

to DLVO theory, a theory by Derjaguin, Verwey, Landau, and Overbeek which is

explained by Hunter et al. [51], pH of stable nanofluids lies in between 2 to 7. Most

nanofluids that have pH in between 2 to 7 display good dispersion and stability. Therefore

it can be concluded that Ag2O-NaCl nanofluids stability can be improved in terms of

reducing the agglomeration further.

Figure 52 : Sedimentation after 4 hours

74

6.4 Errors

6.4.1 Systematic errors

In this experiment, there are few errors that might affect the accuracy of the results.

Firstly is the sonicator breakdown. For first three volume fraction of Ag2O-NaCl nanofluids

which are 0.05%, 0.1% and 0.2%, thermal conductivity is taken in the range of 30 to 80

degree celcius while for volume fraction of 0.3% and 0.5%, thermal conductivity is taken

in the range of 30 to 70 degree. This is because after three experiments is done, Qsonica Q

700 Sonicator is sent for repairing due to a breakdown. After repairing, the samples cannot

reach temperature more than 70 degree celcius after undergoing five hours of sonication.

Therefore Qsonica Q700 operates at different efficiency before and after repairing which

affects the accuracy of the result. Besides that, KS-1 needle might not be completely in the

middle of nanofluids when taking reading hence reducing the accuracy of the results.

6.4.2 Random errors

There are several random errors in this experiment. One of it is when taking thermal

conductivity, viscosity and pH reading, there are some vibration from surrounding air as

well as air conditioning in the lab. Therefore this will reduce the precision of the results.

Besides that, when preparing the samples, nanoparticles are placed on a parafilm on the

weighing machine. Hence when nanoparticles are place inside base fluids, little of

nanoparticles stick at parafilm which reduces the accuracy of the result. During sonication,

the base fluids will evaporates through the hole of aluminium foil and there will be some

base fluid loss during experiment. This also possibly contributed to the random error in the

experiment.

75

Chapter 7

CONCLUSION

7.1 Conclusions

In conclusion objectives are met. Heat transfer characteristics of nanoparticles

dispersed in inorganic mixtures are obtained using silver(I) oxide as nanoparticles and

sodium chloride as inorganic mixture.

This experiment shows that as volume fraction and temperature increase, thermal

conductivities also increase. This is because as volume fraction and temperature increase,

random motion of particles in nanofluids which is also known as Brownian motion also

increases. This then increase the thermal conductivity of nanofluids. Highest thermal

conductivity achieved for silver nanofluids is 192.3% at volume fraction 0.5% and

temperature of 61.13 degree celcius which is very high.

This experiment also shows that as volume fraction increase, viscosity decreases.

This is because molecular attraction between molecules becomes higher. On the other hand,

as temperature increase, viscosity decreases. This is because molecular attractions between

molecules become weaker hence giving lower viscosity value. Silver nanofluids exhibit

excellent viscosity attributes as it has lower viscosity than the base fluids at every volume

fractions.

Finally, pHs of nanofluids are found to be in the range of 6.98 to 7.2 in this

experiment for all volume fraction. Therefore nanofluids formed are a neutral solution.

Overall, combination of silver nanoparticles and sodium chloride mixture shows promising

heat transfer characteristics.

76

7.2 Recommendation for future work

Although nanofluids show great potential in experimentally, problem such as

agglomeration and instability of nanofluids still occurs. Therefore in future experiment,

additives can be used to improve the stability of nanofluids and reduce agglomeration. This

works focus mostly on effect of temperature and volume fraction on thermal conductivity

and viscosity of nanofluids. Hence future research should consider other factor such as

effect of nanoparticles shape and size on thermal conductivity and viscosity of nanofluids.

Besides that, there are many researches done using metal oxide as nanoparticles. In

future, more research can be done using carbon base nanoparticles to compare their

efficiency with metal oxide nanofluids. In addition, findings from researchers seem to

contradict with each other. Therefore a more detailed characterization of nanoparticles

needs to be looked at to explain the difference in findings. A theoretical model needs to be

developed to explain the general behavior of nanofluids.

77

Chapter 8

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82

Nomenclature

NaCl Sodium Chloride

Ag2O Silver(I) Oxide

φ Volume fraction

V Volume (mL)

M mass (kg)

mL milliliter

ρ density (kg/m3)

Knanofluid Thermal Conductivity for nanofluids

Kbasefluid Thermal Conductivity for base fluids

Vnanofluid Viscosity for nanofluids

Vbasefluid Viscosity for base fluids

pH Potential Hydrogen

m mili

Pa Pascal

K Kelvin

s seconds

83

APPENDICES

Appendix A1: Mass of Silver(I) oxide at volume fraction 0.1%

a. Volume concentration (φ = Vnanoparticles / Vbase fluids x 100)

b. φ = 0.1%

c. V basefluid = 120 mL

d. Density of Al2O, = 7.143 g/mL

Mass of nanoparticles is calculated using,

84

Appendix A2: Mass of Silver(I) oxide at volume fraction 0.2%

a. Volume concentration (φ = Vnanoparticles / Vbase fluids x 100)

b. φ = 0.2%

c. V basefluid = 120 mL

d. Density of Al2O, = 7.143 g/mL

Mass of nanoparticles is calculated using,

85

Appendix A3: Mass of Silver(I) oxide at volume fraction 0.3%

a. Volume concentration (φ = Vnanoparticles / Vbase fluids x 100)

b. φ = 0.3%

c. V basefluid = 120 mL

d. Density of Al2O, = 7.143 g/mL

Mass of nanoparticles is calculated using,

86

Appendix A4: Mass of Silver(I) oxide at volume fraction 0.5%

a. Volume concentration (φ = Vnanoparticles / Vbase fluids x 100)

b. φ = 0.5%

c. V basefluid = 120 mL

d. Density of Al2O, = 7.143 g/mL

Mass of nanoparticles is calculated using,

87

Appendix A4: Difference in thermal conductivity for different sonication time

Figure A4: Thermal conductivity at sonication time of 3, 4 and 5 hours

0.3

0.35

0.4

0.45

0.5

0.55

0.6

0.65

0.7

0.75

30 40 50 60 70 80

The

rmal

co

nd

uct

ivit

y (W

/mK

)

Temperatur

Thermal Conductivity at different sonication time

3 hours

4 hours

5 hours