Optical Thermal Lens Technique To Measure Thermo-Optical Properties of

Nano-Engine Oil Lubricant

Faris Mohammed Ali

Department of Communication, Engineering Technical college\Najaf, Al-Fourat Al-Awssat Technical University, Kufa, Najaf, Iraq

E-mail\ faris.m.n@etcn.edu.iq , fawal2003@yahoo.com

HP:009647704149998

Abstract:

Nano engine oil (Nanofluids), a mixture of nanoparticles or nanotube and fluids,

have exceptional potential to enhancement their thermal properties. The single wall

carbon nanotube (SWNT) was suspended in engine oil lubricant: Fuchs TITAN

universal HD SAE 10w/30 and Fuchs TITAN GT1 pro-flex SAE 5w/30 with 0.5%

volume fraction, and Titanium dioxide (TiO2) 18 nm was suspended in engine oil

lubricant: Fuchs TITAN universal HD SAE 10w/30 and Fuchs TITAN GT1 pro-flex

SAE 5w/30 with 0.2% volume fraction. Sonication processing with high-powered

pulses was used to ensure the dispersion of nanotube and nanoparticles in good

uniformity in the engine oil lubricant. The optical thermal lens technique was used to

measure thermo-optical properties of nano-engine oil lubricant. The results show that

the thermo-optical properties of the samples have higher than the base fluid (engine

oil). In addition to, the particles materials have significant influence on thermo-optical

properties, where it is increased with the single walled carbon nanotubes more than

titanium dioxide nanoparticles.

Introduction:

superlative performance cooling is one of the most essential needs of many industrial

technologies[1]. However, a primary limitation in developing energy efficient heat

transfer fluids which have low thermal conductivity required for superlative

performance cooling. wherefore, modern nanotechnology can produce nonmetallic or

metallic particles of nano size dimensions, these nanomaterials have unique thermal,

optical, mechanical, electrical and magnetic properties. Therefore, nanofluids can be

produced by suspending nanomaterials with average sizes below 100 nm in base

fluids [2]. The use of nanofluids in heat exchangers, especially in micro-cooling

systems, may result in energy and cost savings and should facilitate the trend of

device miniaturization [3]. The experimental work has been focused on measurements

of thermal conductivity as a function of type of nanoparticles, size, concentration,

and temperature. The most popular techniques for measuring thermal properties of

nanofluids are the transient hot-wire method [4; 5; 6; 7; 8] 3-ω method [9; 10] and

temperature oscillation method [11; 12]. The effective thermal diffusivities and

thermal conductivities of nanofluids were typically measured using a transient hot

wire (THW) method, which is regard one of the most accurate ways to determine the

thermal properties of nanofluids [13]. The enhancement of thermal conductivity of

CuO-water, Al2O3-water and Cu-Oil nanofluids have been reported by Eastman and

Choi [14] by using the transient hot wire THW method. Ehsan-o-llah Ettefaghi et al.

have used Multi-walled carbon nanotube (MWCNTs) dispersed in engine oil SAE 20

W 50 as base fluid which is prepared by planetary ball mill. They have reported the

thermal conductivity increased by 22.7% at 0.5 wt% concentration and the amount of

flash point and pour point increased by 13% and 3.3%, respectively [15].

The hot wire-laser beam displacement technique have been proposed by Faris

Mohammed A. and W. Mahmood Mat Yunus to measure thermal diffusivity and

thermal conductivity of the aluminum and aluminum oxide nanoparticles dispersed

inside distilled water, ethylene glycol (EG), and ethanol base fluids. They found that

that the thermal conductivity and thermal diffusivity increased linearly with

increasing volume fraction concentration of nanoparticles in the respective base

fluids. In addition, the thermal conductivity and thermal diffusivity increased faster in

the Al2O3 nanofluids than in all the three base fluids [16].

Mohammad hassan Vasheghani et al. studied the effect of Al2O3 phases on the

enhancement of thermal conductivity and viscosity of nanofluids in engine oil by

using hot wire method, their results showed that by adding 4wt% of α-Al2O3 and ɤ-

Al2O3 nanoparticles to the base fluid engine oil thermal conductivity have increased

by 31% and 37%, respectively. In addition, they were observed that the differences in

thermal conductivity comes from higher specific surface area of ɤ-Al2O3 compared to

the α-Al2O3 which is the result of porosity difference [17]. Karthik R. et al. [18] have

investigated the enhancement thermal conductivity of copper (II) oxide-DI water

nanofluids using a tailor- made measurement device that uses the 3ω technique, they

concluded that The enhancement in thermal conductivity over the base fluid for the

tested conditions is observed to be 13 to 25%. A comparison between the measured

data and the predicted ones using established correlations reveals that the deviation in

prediction is within ±10%.

Recently a few optical techniques for measuring thermal conductivity or thermal

diffusivity of nanofluids. Putnam et al.[19] have used an optical beam deflection

technique for measurements of the thermal diffusivity of fluid mixtures and

suspensions of nanoparticles with a precision of better than 1% . Venerus et al.

proposed an optical technique called forced Rayleigh scattering to measure thermal

diffusivity of Au nanoparticle suspension in water and an Al2O3 nanoparticle

suspension in a petroleum oil [20]. Shaikh et al. used a modern laser flash technique

(LFA 447) to measure the effective thermal conductivity of exfoliated graphite, heat

treated nanofibers, and CNTs in polyalphaolefin oil as the base fluid [21].

To the best of our knowledge there are few systematic studies of thermal conductivity

and thermal diffusivity reported in the literature regarding the use of single walled

carbon nanotubes (SWCNT) and Titanium dioxide TiO2 suspensions in engine oil

lubricant (SAE 10W30) and (SAE 5W30), particularly at smaller volume.

In the present work a new model of optical thermal lens technique was developed for

measuring new thermo-optical properties of nanofluids.

Materials and Methods:

1- Theory

The optical thermal techniques have used electromagnetic radiation to induce non

radiative de-excitation of excited states which have led to change in temperature of

sample. This a rise in temperature can be measured by different techniques, these

techniques have used laser beam as the excitation. Optical thermal lens techniques

deserve attention because it is a high sensitivity optical technique. Furthermore, it is

noninvasive, nondestructive, considerably faster and simpler than photothermal

techniques which reported previously [19-21] and it does not require any particular

sample treatment.in addition, it reduces the heat transfer due to radiation and

convection when compared to steady state techniques, since it consists of a transient

method. Indeed, it has been used to obtain optical and thermal properties at room

temperature of nanofluids and nanomaterials.

The optical thermal lens effect is caused by the deposition of heat via non-radiative

decay processes after the laser beam has been absorbed by the sample which has

Gaussian intensity profile (TEM00).

The first step in the development of the optical thermal lens model is to consider the

heat source profile Q(r) is proportional to the Gaussian intensity profile, which can

be expressed as:

I e (r )=(2 Pe

πwe2 )exp ¿) (1)

Where, Pe (mW) is the excitation laser power, we (µm) is the excitation beam waist at

the sample position.

By the heat conduction equation which is depend on the employed boundary

condition that have been developed the infinitive aberrant model for the optical mode

mismatched thermal lens configuration. Using the conditions

∆ T (r ,0 )=0 , (r<∞ )∧∆ T ( ∞, t )=0 , ( t>0 ) , the temporal evolution of the temperature

profile ∆ T (r ,t )in the sample is given by [22]

∆ T (r ,t )=2P e A e

πCρw e2∗∫

0

t

¿¿ (2)

In which Ae the optical absorption coefficient at the excitation beam wavelength (cm-

1 ), C the specific heat (J K-1 g-1 ), ρ is the density (g cm-3) and tc the characteristic

optical thermal lens time constant (s) which is defined by:

t c=w e

2

4 D; D= K

ρC (3)

Where D is thermal diffusivity (m2 s-1) and K is thermal conductivity (W/ m. K).

The temperature evolution of the optical thermal lens depends on the parameter tc

given by Eq. (3), which is related to the thermal diffusivity D. Therefore, parameters

Ae and D which are related to the amplitude and tc of the optical thermal lens signal,

respectively, can be determined by optical thermal lens experiment.

However, this temperature rise, which carries a Gaussian profile, induces a slight

distortion in the probe beam wave front that can be associated with the optical path

length change of the sample with respect to the axis of the beam as:

Φ λp

2 π=l0( ds

dT )p

[∆ T (r , t )−∆ T (0 , t)] (4)

In which Φ is the phase shift induced when the probe beam passes through the optical

thermal lens,λ p is the probe beam wavelength, l0 is the sample thickness and ( dsdT )

p is

the temperature coefficient of the optical length at the probe beam wavelength.

Finally, using Fresnell diffraction theory, the probe beam intensity at the detector

plane can be written as an analytical expression for absolute determination of the

thermo-optical properties of the sample as [22];

I ( t )=I (0)¿¿ (5)

Where, m=(wp

we)

2

and V=Z1

Zc in which Zc≪Z2 .

Here,

Here, w p (µm) is the probe beam radius at the nanofluid sample, Zc is the confocal

distance of the probe beam, Z1 is the distance from the probe beam waist to the

nanofluid sample, Z2 the distance between the nanofluid sample and the detector, I(t)

is the temporal dependence of the probe beam intensity at the detector, I(0) is the

initial value of I(t), and I(0) equal to I(t) when the transient time t or θ is 0, and θ is

approximately the thermally induced phase shift of the probe beam (at r = 0 and

r =√2 we ) after passing through the nanofluid sample, which is given by:

θ=−Pe Ae l0

K λp( ds

dT )p (6)

It is important to note that the parameter ( dsdT ) have described the whole optical path

length change induced by the excitation beam, that means for nanofluid samples

(liquid) we have ( dsdT )=( dn

dT ). While, for solid material it depends on several

mechanisms such as the stress optical coefficient, end-face curvature, and the sample

bulging during the illumination.

By using least square curve fitting of the optical thermal lens experimental data with

Eq.(5), tc and θ can be determined.

In this project, we have used Zc is (2.5 cm), Z1 is (5.5 cm), w p is (198 µm) and w eis (45

µm). Therefore, m is 19.36, V is 2.2.

2- Experiment

The schematic diagram of the optical mode mismatched thermal lens experimental

setup is shown in Figure 1, where these mode configuration has been shown the most

sensitive experimental setup for the optical mismatched thermal lens measurements.

This experimental arrangement used two laser beams with different spot sizes at the

nanofluids sample position as shown in Figure 2. The measurement was performed

by a CW He-Ne (2 mW) laser operated at wavelength of 632.8 nm was used as a

probe laser beam and a 165 LG Argon-Ion laser (10 mW ) operated at wavelength of

514 nm was used as an excitation source . The lasers were mounted on a stage

completed with alignment facilities.

The optical mode mismatched thermal lens measurements were performed using time

resolved method. The time-resolved method permits the measurement of the

development of the thermal lens in a short period of time, and the advantage of this

procedure is that it allows to measure the sample thermal diffusivity.

The excitation laser beam was modulated by Shutter System SR470 then the

excitation beam was focused by a lens (Plano-Convex PCX1304) of focal length of

50 mm to focus the excitation beam onto a nanofluids sample which is resides in a

Cole-Parmer quartz cell with dimension of (20.5 x 10.5) mm. The quartz cell was

fixed on a three-dimension position mechanism stage .The probe beam (He-Ne ) laser

was focused by a lens (Plano-Convex PCX1304) of 60 mm focal length away from

the quartz cell and it is aligned at a small angle (about 2°) with respect to the

excitation beam. A pinhole positioned in front of the position sensitive detector

(PSD, S1880) (PSD2) to select the probe beam central part only.

the excitation beam is used to induce the thermal lens in the central part of the probe

beam and a consequent change in its intensity in the position sensitive detector, PSD1.

The output voltage of the position sensitive detectors (PSDs) were coupled to a digital

storage oscilloscope (Lecroy 9310A) to record the time evolution of TL signal. The

LABVIEW software was used to capture the TL data from oscilloscope.

Computer

Oscilloscope

Pinhole

He-Ne probe Beam Laser)Sample (Quartz

Cell

Mirror 3

Mirror 1 Ar+ Excitation Laser

Mirror 2

Lens 1Shutter

Lens 2

PSD 1

PSD 2

Fig. 1 Schematic diagram of the optical mode mismatched thermal lens experimental

setup

Fig. 2 Geometric diagram excitation and probe beams position

3- Prepare of Nanofluid Samples

Nanofluids sample are prepared by using one step technique method, similar to the

one reported by Choi [23]. With single step method (one step) technique the

nanoparticles are directly dispersed in the base fluids in a single process. The single

wall carbon nanotube (SWNT), 0.7-1.3 nm diameter (704113 ALDRICH, Sigma

Aldrich Co. LLC, Malaysia), Titanium dioxide (TiO2), 18 nm (798525 ALDRICH,

Sigma Aldrich Co. LLC, Malaysia) were suspended in engine oil lubricant as base

fluid: Fuchs TITAN universal HD SAE 10w/30 and Fuchs TITAN GT1 pro-flex SAE

5w/30. The single wall carbon nanotube of volume fraction 0.5%, Titanium dioxide

(TiO2) of volume fraction 0.2% nanoparticles are dispersed in engine oil lubricant

were mixed and kept in an ultrasonic bath (SW12H) for more than 3 hours to ensure

properly dispersion. Furthermore, the nanofluids is subjected to intensified ultra-

sonication by immersing a probe type sonication (Scientz-IID, 950W) for 6 hours to

Wp Lens 2Lens 1

)Sample (Quartz Cell

w0

Z1

achieve maximum possible de-agglomeration of particles. sodium deoxycholate

(DOC) was used as a surfactant for the mixture SWNT with engine oil lubricant as

reported by Wenseleers et al. [24], while, hexadecyltrimethylammonium bromide

(CTAB) was used as a surfactant for the mixture Titanium dioxide (TiO2) with engine

oil lubricant. A Transmission Electronic Microscopy TEM (Hitachi 7100 TEM) was

used to measure the particle size, the particle distribution, and the morphology of

SWNT and nanoparticles in the base fluids (engine oil lubricant).as shown in Figure

1-4.

Fig.1 TEM image single wall carbon nanotube (SWNT) dispersed in Fuchs TITAN

universal HD SAE 10w/30 at volume fraction 0.5 %

100 nm

Fig.2 TEM image single wall carbon nanotube (SWNT) dispersed in Fuchs TITAN

GT1 pro-flex SAE 5w/30 at volume fraction 0.5 %

Fig.3 TEM image Titanium dioxide (TiO2) dispersed in Fuchs TITAN universal HD

SAE 10w/30 at volume fraction 0.2 %

Fig.4 TEM image Titanium dioxide (TiO2) dispersed in Fuchs TITAN GT1 pro-flex

SAE 5w/30 at volume fraction 0.2 %

Result and Discussion

The optical thermal lens effect of nanofluids was based on their laser induced heating

and time resolved monitoring on the thermal effects. So, to verify and evaluate the

25 nm

50 nm

reliability of the experimental measurement of optical thermal lens, firstly we measure

the thermo-optical properties of engine oil lubricant unused, then compare this result

with the literature result of engine oil lubricant and showed a good agreement with

references [25; 26; 27] . The results have shown in Table 1.

Table 1 Results of engine oil lubricant unused

engine oilThermal

Diffusivity x10-8

(m2/s)

Reference value of Thermal

Diffusivity x10-8

(m2/s)

Thermal Conductivity

(W/m.K)

Reference value of `(W/m.K)

Fuchs TITAN SAE 10w/30

8.54 8.5325

8.5326

8.5527

0.144 0.14425

0.14527

Fuchs TITAN SAE 5w/30

8.57 8.5525

8.57270.145 0.14426

0.14627

The measurement of the thermo-optical properties of single walled carbon nanotube

SWNT (0.7-1.3 nm diameter) and Titanium dioxide TiO2 (18 nm) suspension in

engine oil lubricant which are Fuchs TITAN SAE 10w/30 and Fuchs TITAN SAE

5w/30 nanofluid samples were conducted. The single walled carbon nanotube SWNT

were prepared at volume fraction 0.5% and Titanium dioxide were prepared at

volume fraction 0.2% suspension in different engine oil as base fluids; Fuchs TITAN

SAE 10w/30 and Fuchs TITAN SAE 5w/30.

Figures 1 to 4 show TEM for the SWNT and TiO2 nanoparticle distribution of the

sample in engine oil as base fluids (Fuchs TITAN SAE 10w/30 and Fuchs TITAN

SAE 5w/30) after 9 hours in the sonication process (ultrasonic bath and probe type

sonication). The images 1 and 2 show that the SWNT were aggregated to form

nanotubes clusters and evenly distributed in the engine oil base fluids. These TEM

images reveal that the single walled carbon nanotube are highly cluster-dispersed.

while, the images 3 and 4 show that the TiO2 nanoparticles were aggregated to form

nanoparticle clusters and evenly distributed in the engine oil. These TEM images

show that the nanoparticles are highly cluster-dispersed with an average size of about

25-50 nm and are spherical in shape.

The thermally induced phase shift of the probe beam θ and the characteristic optical

thermal lens time constant tc were obtained by fitting equation 5 to the normalized

optical thermal lens time evolution data and finally the thermo physical properties

(thermal diffusivity and thermal conductivity) can be calculated from equation 3.

Where, the specific heat Cp have been determined by ordinary calorimetry and the

density ρ have been determined by Archimedes' method. the experimental have been

conducted at room temperature. Figures 5 and 6 show the typical time evolution of

optical thermal lens signals for the SWNT nano-lubricant engine oil (Fuchs TITAN

SAE 10w/30) and TiO2 nano-lubricant engine oil (Fuchs TITAN SAE 5w/30) samples

respectively, where the solid line represent the best fit of equation 5 to the

experimental data and the symbols (o) denote to the experimental data.

The thermo-optical properties of nano-lubricant engine oil samples have listed in

Table 2.

Table 2 Results of thermo-optical properties of nano-lubricant engine oil

Nanofluid samples θ tc (s)Thermal

Diffusivity x10-8

(m2/s)

Thermal Conductivity (W/m.K)

SWNT+SAE 10w/30 0.09861±0.0002 0.00342±0.00001

14.64±0.114 0.465 ±0.002

SWNT+ SAE 5w/30 0.09135±0.0001 0.00332±0.00003

15.23±0.158 0.489±0.003

TiO2+ SAE 10w/30 0.08736±0.0001 0.00441±0.00002

11.47±0.245 0.291±0.001

TiO2+ SAE 5w/30 0.08487±0.0003 0.00427±0.00004

11.83±0.188 0.315±0.003

The results of thermal diffusivity of SWNT (0.7-1.3 nm diameter) Nanotubes

dispersion in Fuchs TITAN SAE 10w/30 and Fuchs TITAN SAE 5w/30 at volume

fraction 0.5% were 14.64 x 10-8 ± 0.114, 15.23 x 10-8 ± 0.158 (m2/s) respectively.

while Thermal conductivity were 0.465 ±0.002, 0.489±0.003 (W/m.K) respectively.

In addition, The results of thermal diffusivity of TiO2 (18 nm) nanoparticles

dispersion in Fuchs TITAN SAE 10w/30 and Fuchs TITAN SAE 5w/30 at volume

fraction 0.2% were 11.47 x 10-8 ± 0.245, 11.83 x 10-8 ± 0.188 (m2/s) respectively.

While, thermal conductivity were 0.291±0.001, 0.315±0.003 (W/m.K) respectively.

So, the enhancements in thermal diffusivity and thermal conductivity have an obvious

increase by adding nanotubes and nanoparticles. This observation can provide an

insight into the mechanism of thermal exchanger transport in nanofluids. We

particularly mention the volume fraction of nanoparticles or nanotubes dependence of

thermal diffusivity and thermal conductivity, because thermal diffusivity and

conductivity would show more enhancements if the nanoparticles or nanotubes

formed suspensions in base fluids (engine oil). Single Walled Carbon Nanotubes

(SWNT) nanofluid exhibits 71.42% enhancement in thermal diffusivity with 0.5%

volume fraction of nanotubes in Fuchs TITAN universal HD SAE 10w/30, while

Single Walled Carbon Nanotubes (SWNT) nanofluid presents 77.71% enhancement

with 0.5% volume fraction nanotubes in Fuchs TITAN GT1 pro-flex SAE 5w/30.

Moreover, the enhancement in thermal conductivity were 222.91% and 237.24% for

SWNT suspension in Fuchs TITAN universal HD SAE 10w/30 and SWNT

suspension in Fuchs TITAN GT1 pro-flex SAE 5w/30 respectively.

The enhancement of thermo physical properties (diffusivity and conductivity) of TiO2

nanofluids suspension in Fuchs TITAN universal HD SAE 10w/30 and Fuchs TITAN

GT1 pro-flex SAE 5w/30 at volume fraction 0.2% were 34.3%, 38.03%, 102.08%,

and 117.24%, respectively. We observed also that SWNT suspension in Fuchs TITAN

GT1 pro-flex SAE 5w/30 have higher thermal diffusivity and thermal conductivity

values compared to the TiO2 nanoparticles in Fuchs TITAN GT1 pro-flex SAE 5w/30.

The comparison between thermal diffusivity and conductivity of SWNT and TiO2

nanofluids in different base fluid at same volume fraction, the Fuchs TITAN GT1 pro-

flex SAE 5w/30 base fluid has the highest thermal diffusivity and thermal

conductivity. According to the results which are presented above, the nano (nanotube

and nanoparticle) suspension in engine oil demonstrates some unique and novel

thermal properties when compared to the traditional heat transfer of engine oil. There

are several mechanisms that will enhance the thermal properties of nano-engine oil:

Brownian motion of nano, interfacial liquid layer (liquid layer at liquid particle

interface), nano- structuring / aggregation, and effects of nano clustering [28; 29].

First, Brownian motion, by which nano move through the fluid and possibly collide,

thereby enabling direct solid-solid transport of heat from one to another, can be

expected to increase thermophysical properties of nanofluid. Brownian motion of

nano could contribute to the thermophysical enhancement through two ways, direct

contribution due to motion of nano that transports heat, and indirect contribution due

to micro-convection or nano-convection of fluid surrounding individual nano. The

direct contribution of Brownian motion has been taken by comparing the time scale of

particle motion with that of heat diffusion in the fluid. Equivalently we can compare

the time required for particle to move by the distance equal to its size with time

required for heat to move in the liquid by the same distance. The indirect contribution

has also been shown to play a minute role through the same reasoning for the direct

contribution and also through molecular modeling[28; 29; 30; 31].Second reason,

which is important for the enhancement thermal diffusivity and thermal conductivity

of the nanofluid, interfacial liquid layer or some time called (liquid layer at liquid

particle interface) would lead to an Increase in the estimate value of thermal

diffusivity and thermal conductivity of nanofluid and an increase thermal diffusivity

and thermal conductivity with increase particle size. Considering that the molecular

structure of liquid at the solid interface is more ordered, possibilities of larger thermal

conductivity of this ordered liquid layer and 'tunneling' of heat carrying phonons from

one particle to another were put forward. For strong solid–liquid interactions, typical

of those in nanofluids with metallic nanoparticles, a percolating network of

amorphous-like fluid structures can emerge which can facilitate additional thermal

conduction paths [31]. However, an interface effect that could enhance thermal

conductivity is the layering of the fluid at the solid interface, by which the atomic

structure of the liquid layer is significantly more ordered than that of bulk liquid.

Given that crystalline solids (which are obviously ordered) display much better

thermal transport than liquids, such liquid layering at the interface would be expected

to lead to a higher thermal conductivity. To evaluate an upper limit for the effect of

the interfacial layer, we suppose that the thermal conductivity of this interfacial fluid is

exactly the same as that of the solid nanoparticle. The resultant larger effective volume

of the nanoparticle-layered-fluid structure could enhance the thermal conductivity of

nanofluid. Third reason of enhancement thermophysical properties of nanofluids is the

nano structuring / aggregation have dominated mechanism for the thermophysical

properties enhancement of nanofluids, due to interconnected nano in the fluid

enhances the thermophysical properties. The nano-agglomeration is a similar process

for nano to settle in the fluid due to the larger mass that results in a particle gradient in

the fluid. The “particle free” zone has a higher thermal resistance compared to the

particle rich zone. The suppression of agglomeration of the nanoparticles is also very

important for designing effective heat transport nanofluids. It is understood that the

heat transfer can be much faster along the backbone of the agglomeration. Finally,

Clustering of the nano becomes more effective in fluids with a higher volume

fraction. This clustering has a major effect on thermophysical properties

measurements of the nanofluid. By creating paths of lower thermal conductivity

resistance, clustering of particles into percolating would have a major effect on the

thermophysical properties. The effective volume of the cluster, i.e., the volume from

which other clusters are excluded, can be much larger than the physical volume of the

particles. Since within such clusters heat can move very rapidly, the volume fraction

of the highly conductive phase is larger than the volume of the solid, which

significantly increases thermophysical properties.

-0.2 0 0.2 0.4 0.6 0.8 1 1.2 1.40.445

0.45

0.455

0.46

0.465

0.47

0.475

0.48

0.485

0.49 Theoretical Optical Thermal LensExperimental Data

O p ti c al

T h er m al

L e n s Si g n al

(a r b.

u m it s)

Time(s)

Fig. 5 time evolution of optical thermal lens signals for the SWNT nano-lubricant engine oil Fuchs TITAN SAE 10w/30

-0.2 0 0.2 0.4 0.6 0.8 1 1.20.47

0.475

0.48

0.485

0.49

0.495

0.5

0.505

0.51Theoretical Optical Thermal lens

Experimental dataO

ptica

l Ther

mal

Len

s Si

gnal

(a

rb.

umits

)

Time(s

Fig. 6 time evolution of optical thermal lens signals for the TiO2 nano-lubricant engine oil Fuchs

TITAN SAE 5w/30

Conclusions:

This study have been discussed the use of optical thermal lens technique for the

investigation of the thermo-optical properties of nano-engine oil lubricant. optical

thermal lens technique provides a fast and precise technique to determine absolute

values of thermo-optical properties of nano-engine oil lubricant. Thus, the optical

thermal lens technique is a new technique to study thermo-optical properties of nano-

engine oil lubricant. Optical thermal lens technique is advantageous as it is non-

contacting and can be used in thick samples as well as in thin films. However it

requires laser beams with good transverse mode (close to TEM00). The thermo-optical

properties for Single walled carbon nanotube SWNT (0.7-1.3 nm diameter) and

titanium dioxide TiO2 (18 nm) suspension in engine oil lubricant (Fuchs TITAN

universal HD SAE 10w/30 and Fuchs TITAN GT1 pro-flex SAE 5w/30 ) were

determined. However, to the best of our knowledge these nano engine oil lubricant

samples which were used in this study were new samples, therefore, the values of the

thermo-optical properties of these nano engine oil samples are new.

The results show that the thermo-optical properties of all samples of nanofluid have

higher than the base fluid (engine oil). In addition to, the particles materials have

significant influence on thermo-optical properties, where it is increased with the

single walled carbon nanotubes more than titanium dioxide nanoparticles as shown in

results. The covering of nanoparticles type plays an important role in their thermal

properties.

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