heat transfer of nanofluids through

8/7/2019 HEAT TRANSFER OF NANOFLUIDS THROUGH

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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


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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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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


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EXPERIMENTAL SETUP:

Figure.3


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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 theflowmeter2 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 40c 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 50c and60c 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 .

oo

io

iiAhkL

DD

AhUA .

1

2

)/ln(

.

11!

T


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RESULTS AND DISCUSSIONS:

1.40oC

Isolator(1) Convection

on the tube

(3) convection on the

annulus

(2) conduction

in the tube wall

iiAh .

1

kL

DDio

T2

)/ln(

ooAh .

1


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2.50oC

3.60oC


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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:

4.09238.0001.06886.0 PrRe)6286.70.1(0059.0 nfnfdPeNu J!

nf

pm

d

due

E

!

nf

mnf

Du

Y

!Renf

nf

nfE

Y

Pr


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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.

70

80

90

100

110

120

130

140

150

160

10,000 15,000 20,000 25,000 30,000 35,000

Reynolds number, Re

NusseltNumber,Nu

Nano 1%40 C

Nano 1%50 C

Nano 1%60 C


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heat transfer of nanofluids through

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