HEAT TRANSFER OF NANOFLUIDS THROUGH

DOUBLE PIPE HEAT XCHANGER

ABSTRACT:

Due to the various speculated uses of nanofluids, it has become important to know more about their properties hence the objective of the present study is to investigate the forced convection of nanofluids.

The investigation was conducted by using double pipe heat exchanger in counter flow arrangement and the flow was turbulent. Water based nanofluids containing Al2O3 nanoparticles of various concentrations will be tested.

INTRODUCTION:

Nanofluids are dispersions of nanometer sized metal/metal oxide, carbon nanotubes, diamond or any other nanoparticles in a liquid medium.

These fluids have shown a significant increase in the thermal conductivity compared to the base fluid.

These fluids have a great potential to replace current coolants and heat transfer fluids in a variety of applications.

Heat-Transfer Challenges:

The heat rejection requirements are continually increasing due to trends toward smaller features (to <100 nm) for microelectronic devices, more power output for engines.

Cooling becomes one of the top technical challenges facing high-tech industries such as microelectronics, transportation, manufacturing, and metrology.

Conventional method to increase heat flux rates:

extended surfaces such as fins and micro-channels

increasing flow rates increases pumping power.

Nanofluids are promising to meet and enhance the challenges

Why use nanoparticles?

The concept of dispersing solid particles in fluids to enhance thermal conductivity is not new-it can be traced back to Maxwell

The major problem is the rapid settling of these particles (mm or micro) in fluids.

The small size of nanoparticles should markedly improve the stability of suspensions

The agglomeration of nanoparticles into larger particles that are found in liquids is a serious challenge.

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Materials for Nanoparticles and BaseFluidsMaterials for nanoparticles and base fluids are diverse:1. Nanoparticle materials include:Oxide ceramics – Al2O3, CuOMetal carbides – SiCNitrides – AlN, SiNMetals – Al, CuNonmetals – Graphite, carbon nanotubesLayered – Al + Al2O3, Cu + CPCM – S/SFunctionalized nanoparticles2. Base fluids include:WaterEthylene- or tri-ethylene-glycols and other coolantsOil and other lubricantsBio-fluidsPolymer solutions

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Concept of NanofluidsConventional heat transfer fluids have inherently poor thermal conductivity compared to solids.Conventional fluids that contain mm- or m-sized particles do not work with the emerging “miniaturized” technologies because they can clog the tiny channels of these devices.Modern nanotechnology provides opportunities to produce nanoparticles.Argonne National Lab (Dr. Choi’s team) developed the concept of nanofluids.Nanofluids are a new class of advanced heat-transfer fluids engineered by dispersing nanoparticles smaller than 100 nm (nanometer) in diameter in conventional heat transfer fluids.

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Thermal conductivity of typical materials

Ther

mal

con

duct

ivity

(W/m

-K)

Material

0.15 0.25 0.61

1-Engine Oil2-Ethylene Glycol3-Water4-Alumina5-Silicon6-Aluminum7-Copper8-Silver9-Carbon

Solids have thermal conductivitiesthat are orders of magnitude larger than those of conventional heat transfer fluids.

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Four Characteristic Features of Nanofluids

Pioneering nanofluids research in ANL has inspired physicists, chemists, and engineers around the world.Nanofluids have an unprecedented combination of the four characteristic features desired in energy systems (fluid and thermal systems):Increased thermal conductivity (TC)at low nanoparticle concentrationsStrong temperature-dependent TCNon-linear increase in TC with nanoparticle concentration Increase in boiling critical heat flux (CHF)

These characteristic features of nanofluids make them suitable for the next generation of flow and

heat-transfer fluids.

Figure .1

DOUBLE PIPE HEAT EXCHANGER:

A double pipe heat exchanger, in its simplest form is just one pipe inside another larger pipe.

One fluid flows through the inside pipe and the other flows through the annulus between the two

pipes. The wall of the inner pipe is the heat transfer surface. The pipes are usually doubled back

multiple times as shown in the diagram at the left, in order to make the overall unit more

compact.

The term 'hairpin heat exchanger' is also used for a heat exchanger of the configuration in the

diagram. A hairpin heat exchanger may have only one inside pipe, or it may have multiple inside

tubes, but it will always have the doubling back feature shown. . Some heat exchanger

manufacturers advertise the availability of finned tubes in a hairpin or double pipe heat

exchanger. These would always be longitudinal fins, rather than the more common radial fins

used in a crossflow finned tube heat exchanger. The actual double pipe heat exchanger is as

shown in the figure.2

Figure.2

EXPERIMENTAL SETUP:

Figure.3

Drainase

8

321

15 5

17

14

7

4

9

12

13

6

11

16

Valve 11

Flow meter 210

Computer9

DT 98068

Wheatstone Bridge7

Thermometer T26

Double Pipe Heat Exchanger5

Heater4

Reservoir 13

Pump 12

Thermometer t116

Flow meter 115Thermometer T114

Waste13

Reservoir 212

Pump 211

Thermometer t217

10

AC AC ACAC

18

Valve 218

WORKING:

The experimental setup is as shown in the figure.3 consist of double pie heat exchanger,

computer, two reservoirs, one heater, wheatstone bridge circuit, two pumps, valves etc. The

second reservoir consisting of the nanofluid which is passed through the pum2 through the

flowmeter2 when valve2 is opened. First the nanofluid passthrough the double pipe heat

exchanger through inner pipe of diameter 17mm.The reservoir consisting of the water based

nanofluids AL2O3 nanoparticles. The nanoparticles are of different concentrations like

1%nanofluid and 4%nanofluid is used. The fluid is heated in reservoir2 by using heater and then

send to the double pipe heat exchanger of another side through the pump1, flowmeter1 when

valve1 is opened.

The water is used as the fluid in heat exchanger then the operation is carried out at 40˚c then

the calculations are done by the computer through data transmitter with the required inputs. The

nusselt number and then heat transfer coefficient or film coefficient are determined by using the

Reynolds number and other parameters. Like this at 50˚c and60˚c the values are determined.

The nanofluid1% and 99% water is next used as the fluid of the heat exchanger and then the

properties of the fluid are determined, and then with different concentrations of the nanofluids

are used and then heat transfer rate is determined. The flowmeters are used to find out the flow

of the fluid and then pumps are used to circulating the fluid with the required velocity.

Finally by observing the results the heat transfer rate is increased by using the nanofluids with

different concentrations of nanoparticles with base fluids.

MEASUREMENT OF CONVECTIVE HEAT TRANSFER COEFFICIENT:

By using the below relation we determine the overall heat transfer coefficient .

1UA

= 1hi. Ai

+ln (Do /Di )

2π kL+ 1ho . Ao

Isolator(1) Convection

on the tube

(3) convection on theannulus

(2) conductionin the tube wall

ii Ah .1

kLDD io

2)/ln(

oo Ah .1

RESULTS AND DISCUSSIONS:

1. 40 oC

1 2 3

2. 50 oC

3. 60 oC

TEMPERATURE DEPENDANCE:

Xuan and Li proposed new correlation concerning forced convection of nanofluids flowing in the tube by considering the microconvection and microdiffusion effects of the suspended nanoparticles:

Nu=0 .0059(1. 0+7 . 6286φ0.6886Ped0 . 001)Renf

0 . 9238 Prnf0 . 4

Prnf=υnfαnf

Renf=umDυnf

Ped=umd pα nf

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10,000 15,000 20,000 25,000 30,000 35,000Reynolds number, Re

Nus

selt

Num

ber,

Nu

Nano 1% 40 CNano 1% 50 CNano 1% 60 C

CONCLUSION:

nanofluids have a bright future to be used as an effective heat transfer fluids,

nanofluids with relatively small concentration of solid particle can give meaningful enhancement of convective heat transfer coefficient

the enhancement of heat transfer convective coefficient compared to the base fluids: 6-10% for 1% particles concentration and 7-17% for 4% particles concentration

The use of Al2O3 nanoparticles as dispersed in water can enhance the convective heat transfer coefficient in the turbulent regime and the enhancement increase with Reynolds number, particles volume concentration, and temperature as well under the condition of experiment.