47

Nano Progress Research Article

Nano Prog., (2021) 3(5), 47-52.

DOI: 10.36686/Ariviyal.NP.2021.03.05.026 Nano Prog., (2021) 3(5), 47-52.

Performance Enhancement and Effectiveness of Heat Exchangers Using MWCNT/Graphene Based Nanofluid Ajey C.P.,*

a Girisha Lakshman Naik.,

a Malteshkumar Deshpande.,

a Mahanthesh M.R.

a and Gururaja

L.b

aDepartment of Mechanical Engineering, PES Institute of Technology and Management, Shivamogga, Karnataka, India bDepartment of Mechanical Engineering, PVP Polytechnic, Bengaluru, Karnataka, India

*Corresponding author E-mail address: ajeycp89@gmail.com (Ajey C.P.)

Ariviyal Publishing Journals

ISSN: 2582-1598 Abstract: In many engineering applications, heat exchangers are used to transfer the heat between two mediums, efforts have been made to increase thermal transfer efficiency in heat exchangers to decrease heat transfer time and improve energy effectiveness. Due to the low thermal conductivities of the heat transfer fluids, the performance enhancement and compactness of heat exchangers is not up to the mark. With the increasing requirements of current technology, new kinds of heat transfer liquids need to be developed that are more efficient in the performance of heat transfer. The present work focuses on utilizing nanofluids to check the effectiveness of heat transfer phenomenon. Research shows that adding nanoparticles to the base fluid can improve the fluid's thermal conductivity.

Keywords: Heat exchangers; Nano particles; Nano Fluids

Publication details

Received: 24th February 2021

Revised: 20th April 2021

Accepted: 20th April 2021

Published: 29th April 2021

1. Introduction

One of the significant requirements of many sectors is ultrahigh-

performance cooling. Low thermal conductivity, however, is a main

restriction in the development of energy efficient heat transfer

liquids needed for cooling purposes. Water, oil and ethylene glycol

which are currently being used as coolants are limited by their

decreased thermal conductivity. Research demonstrates that adding

nanoparticles to the base fluid can enhance the thermal conductivity

of the fluid. But nanofluid[1]

conduct during heat transfer, it is also in

the early stages of growth and has not been fully investigated.

Research is required to promote nanotechnology and identify

applications for the heat transfer of nanoparticles/nanofluids. These

are developed by dispersion of nanometer sized materials in the base

liquids. The nano meter sized materials are the one which are having

a dimension at nano level atleast in one direction, such as nano

particles, nanofibers, nanotubes, nano sheets etc. The sort of

nanoparticle used depends directly on enhancing the base fluid’s

necessary property. A single nano material will not possess the

required properties for the required applications. The main objective

of the present work includes preparation of the nanofluids using

graphene, carbon nano tube (CNT) and hybrid[2]

composition of

graphene and carbon nano tubes by dispersing in base fluids such as

distilled water and ethylene glycol. The hybrid nanofluid is expected

to produce better thermal properties compared to individual

nanofluid. The prepared sample is used to determine the thermo

physical properties such as density, kinematic viscosity, dynamic

viscosity and specific heat. The properties obtained with nanofluid

samples are compared with the results of base fluid. Performance

analysis of the prepared sample is carried out using double pipe heat

exchanger[3]

in order to determine the heat transfer rate and

effectiveness in parallel and counter flow application. The results

obtained are compared with the performance of base fluid and

suitable conclusions are drawn.

2. Experimental Section

In order to prepare the nanofluids the graphene and carbon nano

tubes are used with base fluid, the detail descriptions for the same

are as indicated below.

2.1. Carbon Nano Tube

Carbon nanotube[4]

plays a very important role in various fields due

to its excellent mechanical, thermal, electrical, chemical and optical

characteristics. Carbon nanotubes are capable of effectively

conducting electricity and heat therefore these can behave as metals

or semiconductors even they are used in electromechanical actuators

and sensors. The thermal conductivity[5]

values for single-walled

carbon nanotube double walled carbon nanotube and multiwalled

carbon nanotube,[6]

respectively, are 6000 W/mK, 3986 W/mK and

3000W/mK As per these values the very important observation that

can be drawn is that, the thermal conductivity is decreasing with

increase in number of wall layers.

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Nano Prog., (2021) 3(5), 47-52.

2.2. Graphene

For all other dimensional carbon products, graphene[7]

is a 2D

building material. These can be wrapped and rolled to form bucky

balls, 1D and 3D nano materials such as nano tubes and Graphite

respectively. Heat transfer by using graphene material is an ongoing

area of research that has grabbed attention owing to the potential of

thermal management applications. On comparing the early

measurements of graphene and pyrolytic graphite the thermal

conductivities at room temperature of both the materials are found

to be 5300 W/mK and 2000W/mK respectively.

2.3. Base Fluid

The base fluids such as Water, ethylene glycol[8]

or mixture of both

and oils are the most commonly used fluids for nanofluid

preparation. The thermal conductivity values of the base liquids are

usually lesser than metals. Because most metals have greater

thermal conductivity values than base liquids, adding small quantities

of solid particles to base fluids is an efficient strategy for enhancing

liquid heat conductivity. Since the ethylene glycol possess better

thermal properties compared to water, this is commonly used as a

base fluid for nano fluid preparation. For example, in automobiles

and liquid-cooled computers, the major use of ethylene glycol is as a

medium for convective heat transfer. The systems which are

required to cool below freezing water temperature utilize the

ethylene glycol with chilled water. The heat capacity of pure ethylene

glycol is approximately half that of water. Ethylene glycol therefore

reduces the specific heat capacity of water mixtures compared to

pure water while offering freeze protection and an enhanced boiling

point.

3. Nano Fluid Preparation and testing

The major step of the current work is to prepare the nano fluids, the

ethylene glycol and water are used as a base fluid for the same. 0.1

gm of nano particle is combined with 100 ml of base fluid. The

preparation method includes, known quantity of nanoparticle and

base fluids are taken in a beaker and this is subjected to magnetic

stirring action at a specified velocity to accomplish proper mixing of

nano particles with base fluid. This is further processed by sonication

process.

3.1. Sonication Process

Nanofluid preparation is a significant phase hence it is necessary to

carry out the preparatory methods systematically. In the base fluid,

nanoparticles are added and stirred continuously for several hours.

So that nano particles stay in suspension without settling down at

the container's bottom. Both samples of nanofluids based on

graphene and CNT used to estimate their characteristics were

subjected to magnetic stirring, accompanied by ultrasonic vibration

for around 2 to 3 hours. Therefore, prepared nanofluids samples are

deposited for observation and no particle settling is found at the

bottom of the flask after a few hours. To evaluate the thermo-

physical properties, the nanofluids suspension prepared after the

magnetic stirring and sonication technique[9]

is well used.

3.2. Determination of Thermo-Physical Properties

Its density, kinematic viscosity,[10]

dynamic viscosity and specific heat

are the most significant characteristics needed to estimate

nanofluids. For different combinations, the thermal properties of

nanofluids are experimentally carried out and the effects of the

experiments are traced and contrasted with separate nanofluids

samples. The viscosity test for various nanofluids is conducted by

using Saybolt viscometer as shown in Fig. 1. A known sample

quantity is drawn in a beaker and weighing machine is used to

measure the weight. The density of the nanofluid can be readily

determined by understanding the weight and quantity of the sample.

The test is conducted for distinct temperatures and measured the

time taken to collect known quantity (50ml) of nanofluid. The

kinematic and dynamic viscosities are calculated by using the

appropriate formulae. Table 1 Indicates the values obtained during

viscosity test for nano fluids (graphene and ethylene glycol).

Using the appropriate formulas (1) and (2), the densities of

nanofluid at various temperatures are evaluated and the kinematic

viscosity at various temperatures is evaluated using appropriate

correlation (3). The dynamic viscosity can be found by the relation of

density and kinematic viscosity.

kg/m

3 (1)

Where, W1 - weight of the empty jar; W2 - Weight of the jar with

nanofulid. Here, W1 = 49.03 g and W2 = 104.9 g.

Fig. 1. Saybolt Viscometer

Table 1. Testing of graphene and ethylene glycol based nanofluid.

Temp (oC)

Ρ (kg/m3) Time (sec)

S υ(m2/sec)

(10-6) μ

(Ns/m2)

30 1117.40 64 64.32 11.50 0.01285 40 1110.25 57 57.28 9.54 0.01059 50 1103.10 54 54.27 8.67 0.00956 60 1095.95 51 51.23 7.78 0.00853 70 1088.79 46 46.23 6.23 0.00678 80 1081.64 41 41.21 4.58 0.00495

S - Saybolt Number

Table 2. Specific heat values of base fluid and nano fluids Fluid used Specific heat (kJ/kg K)

graphene based nanofluid 2.251 CNT based nanofluid 2.162 graphene/CNT based nanofluid 2.253 Base fluid (ethylene glycol) 2.228

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Ajey et al., Nano Progress

Nano Prog., (2021) 3(5), 47-52.

kg/m3

(2)

υ = 0.226S-195/S for 3<S<100 S= t x 1.005 (3)

Where, - Density at room temperature, - Density of fluid at

given temperature; υ - Kinematic Viscosity. A fluid's dynamic viscosity

reflects its ability to shear flows, where adjacent layers pass at

different speeds parallel to each other. It is calculated by using

equation (4).

Dynamic Viscosity, (4)

One of the key features is specific heat, which plays a major role

in influencing the nanofluids heat transfer rate. Specific heat is the

amount of heat required to raise the temperature of one gram of

fluid by one degree centigrade. Expression (5) is used to calculate the

specific heat when there is a specified volume concentration of

nanoparticles in the base liquid.

Cp=Q/ (m x ΔT) (5)

Where Q= Heat energy in Joules, m=mass of nano particles in

grams, Cp= Specific heat (kJ/kgK), ΔT= Change in temperature. For

graphene based nanofluid test Sample the value of specific heat is

found to be 2.252 kJ/kg K. Similarly the table 2 indicates Specific heat

of nano fluids and base fluid for a heat input of 50W.

Table 3, Table 4 and Table 5 indicate the values of thermo

physical properties for CNT+ethylene glycol, graphene+CNT+ethylene

glycol and ethylene glycol respectively.

3.3. Performance Analysis

Fig. 2 demonstrates the double pipe heat exchanger experimental

configuration for measuring performance parameters. The outer

shell of the pipe consists of GI material with an inner pipe is made up

of copper and having a diameter of 12.5 mm and a length of 1.5 m.

Mineral wool cladding is provided that acts as an insulation over the

external pipe. On each pipe there are two valves that can alternately

be opened and closed for parallel and counter flow arrangements. In

order to supply cold and warm fluid through tubes, two fluid inlets

are provided. Heaters are used to heat inlet water. Thermocouples

are given to evaluate warm and cold water temperatures under

circumstances of inlet and outlet. These temperatures are indicated

by the digital temperature indicator.

The experimental values of graphene nano fluid for parallel and

counter flow are as shown in Table 6 and Table 7 respectively.

LMTD is calculated by equation (6).

LMTD= (θ2- θ1)/ln (θ2/ θ1) (6)

Where LMTD - Logarithmic mean temperature difference, θ2=thi-

tci and θ1=tho-tco for parallel flow and θ2=thi-tco and θ1=tho-tci for

counter flow exchangers.

Overall heat transfer co-efficient (U) is calculated by equation (7)

and (8).

U= Q/ (A x LMTD) (7)

Effectiveness value for different nano fluids can be calculated

using equation (8).

Fig. 2. Heat Exchanger Setup

Table 3. Testing of CNT and ethylene glycol nanofluids. Temp

(C) ρ

(kg/m3) Time for

50ml (sec) S

υ(m2/sec) (10-6)

μ (Ns/m2)

30 1117.40 65 65.33 11.77 0.0109 40 1110.25 60 60.30 10.39 0.00961 50 1103.10 56 56.28 9.25 0.0085 60 1095.95 54 54.27 8.69 0.0079 70 1088.79 49 49.24 7.16 0.0065 80 1081.64 45 45.20 5.9 0.0053

W2=104.9 g Table 4. Testing of graphene/CNT/ethylene glycol nanofluids. Temp (oC)

ρ (kg/m3)

Time for 50ml (sec)

S υ(m2/sec)

(10-6) μ

(Ns/m2)

30 1119.40 65 65.33 11.77 0.01318 40 1112.24 59 59.29 11.11 0.01236 50 1105.07 55 55.28 8.96 0.00990 60 1097.91 49 49.25 7.17 0.00787 70 1090.74 47 47.24 6.55 0.00714 80 1083.58 44 44.22 5.58 0.00605

W2=105 g

Table 5. Thermo-physical properties of ethylene glycol

Temp

(C) ρ (kg/m3)

Time for 50ml (sec)

S υ(m2/sec)

(10-6) μ

(Ns/m2)

30 1084.20 67 67.33 12.32 0.01336 40 1077.26 61 61.31 10.67 0.01149 50 1070.32 56 56.28 9.24 0.00989 60 1063.38 50 50.25 7.47 0.00794 70 1056.44 46 46.23 6.23 0.00658 80 1049.51 44 44.22 5.58 0.00586

W2=103.24 g

Table 6. Experimental test results for graphene nano fluid Type of flow Parallel

Parameter I II

flow rate of Hot water (m3/sec) 40×10-6 50×10-6 flow rate of Cold water (m3/sec) 50×10-6 40×10-6 Inlet Nano fluid temperature (°C)(tci) 37 37.2 Outlet Nano fluid temperature(°C)(tco) 40.7 40.8 Inlet Hot water temperature (°C)(thi) 52 52.2 Outlet Hot water temperature (°C)(tho) 47.8 48

Table 7. Experimental test results for graphene nanofluid

Type of flow Counter

Parameter I II

Hot water flow rate (m3/sec) 40×10-6 50×10-6

Cold water flow rate (m3/sec) 50×10-6 40×10-6 Inlet Nano fluid temperature (°C)(tci) 37.8 37.7 Outlet Nano fluid temperature (°C)(tco) 41.2 50.1 Inlet Hot water temperature (°C)(thi) 53.1 53.2 Outlet Hot water temperature (°C)(tho) 48.6 49.3

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Effectiveness, ε = (thi-tho) / (thi-tci) (8)

Similarly the experimental values for CNT based nano fluid for

parallel and counter flow are as shown in Table 8 and Table 9

respectively. The values of heat transfer rate and effectiveness are as

shown in Table 10.

The hybridising effect of graphene and CNT based nano fluid

gives the following experimental results. The experimental values for

parallel and counter flow are as shown in Table 11 and Table 12

respectively. Heat transfer rate and effectiveness values are as

shown in Table 13.

In order to compare the values with the base fluid the properties

of base fluid and experimental values are considered. Table 14 and

Table 15 show the Experimental test results of distilled water for

parallel and counter flow respectively. The values of heat transfer

rate and effectiveness for the same is as shown in Table 16.

4. Results and Discussions

The feature of heat transfer is a significant phenomenon for fluid

choice. In the current work, the nano particles are mixed to form

nanofluid with two different base fluids, and various experiments are

used to determine the physical properties. The performance analysis

of individual nanofluid and hybrid nanofluid for two distinct

combinations such as parallel and counter flow is performed in a

heat exchanger. For distinct flow conditions, the rate of heat transfer

and effectiveness were analyzed.

4.1. Specific Heat

From the experiment results it is observed that the hybrid nanofluid

exhibit higher specific heat. The nanofluid using carbon nanotube

shows least specific heat value whereas the nanofluid using graphene

alone yields much better specific heat value which is near to the

value obtained using hybrid nanofluid. From the results it is

concluded that the addition of nanoparticles into the base fluid will

enhance the specific heat value.

Table 8. Experimental test results of CNT nanofluid Type of flow Parallel

Parameter I II

Hot water flow rate (m3/sec) 40×10-6 50×10-6 Cold water flow rate (m3/sec) 50×10-6 40×10-6 Inlet Nano fluid temperature (°C)(tci) 37.2 37 Outlet Nano fluid temperature (°C)(tco) 39 39.2 Inlet Hot water temperature (°C)(thi) 53 51.3 Outlet Hot water temperature (°C)(tho) 48.8 46.2

Table 9. Experimental test results of CNT nanofluid

Type of flow Counter

Parameter I II

Hot water flow rate (m3/sec) 40×10-6 50×10-6 Cold water flow rate (m3/sec) 50×10-6 40×10-6 Inlet Nano fluid temperature (°C)(tci) 37.8 38.1 Outlet Nano fluid temperature (°C)(tco) 39.6 39.3 Inlet Hot water temperature (°C) (thi) 54 52.2 Outlet Hot water temperature (°C)(tho) 48.7 46.2

Table 10. Experimental test results for CNT based nanofluid

Flow Parallel Counter

Heat Transfer Rate Q (J/s) 540.10 631.88 Effectiveness 0.266 0.327

Table 11. Experimental test results of graphene/ CNT nanofluid

Type of flow Parallel

Parameter I II

Hot water flow rate (m3/sec) 40×10-6 50×10-6 Cold water flow rate (m3/sec) 50×10-6 40×10-6 Inlet Nano fluid temperature (°C)(tci) 37.2 37.8 Outlet Nano fluid temperature (°C)(tco) 40 41.2 Inlet Hot water temperature (°C)(thi) 53 52.4 Outlet Hot water temperature (°C)(tho) 48.3 49.2

Table 12. Experimental test results of graphene /CNT nanofluid

Type of flow Counter

Parameter I II

Hot water flow rate (m3/sec) 40×10-6 50×10-6 Cold water flow rate (m3/sec) 50×10-6 40×10-6 Inlet Nano fluid temperature (°C)(tci) 37.8 38.1 Outlet Nano fluid temperature (°C)(tco) 39.6 39.2 Inlet Hot water temperature (°C) (thi) 54 52.3 Outlet Hot water temperature (°C)(tho) 49.1 50.9

Table 13. Experimental test results of graphene/CNT nanofluid

Type of Flow Parallel Counter

Heat Transfer Rate Q (J/s) 694.98 632.17 Effectiveness 0.297 0.302

Table 14. Experimental test results of Base fluid (Distilled water)

Type of flow Parallel

Parameter I II

Hot water flow rate (m3/sec) 40×10-6 50×10-6 Cold water flow rate (m3/sec) 50×10-6 40×10-6 Inlet Nano fluid temperature (°C)(tci) 31.7 31.4 Outlet Nano fluid temperature (°C)(tco) 34.5 34.7 Inlet Hot water temperature (°C)(thi) 49.6 46.5 Outlet Hot water temperature (°C)(tho) 45.3 43.8

Table 15. Experimental test results of Base fluid (Distilled water)

Type of flow Counter

Parameter I II

Hot water flow rate (m3/sec) 40×10-6 50×10-6 Cold water flow rate (m3/sec) 50×10-6 40×10-6 Inlet Nano fluid temperature (°C)(tci) 31.8 32 Outlet Nano fluid temperature (°C)(tco) 34.9 34.8 Inlet Hot water temperature (°C) (thi) 50.2 47.3 Outlet Hot water temperature (°C)(tho) 45.6 44

Table 16. Experimental test results for Base fluid (Distilled water)

Type of Flow Parallel Counter

Heat Transfer Rate Q (J/s) 653.11 709.62 Effectiveness 0.24 0.25

Fig. 3. specific heat values

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Nano Prog., (2021) 3(5), 47-52.

4.2. Viscosity

The experiment is performed using the Saybolt viscometer to

determine distinct fluid viscosity. Ethylene glycol is added with

nanoparticles such as graphene and carbon nanotubes, and

nanofluids are tested for flow variation at different temperatures. To

determine viscosity, the base fluid (ethylene glycol) is also tested at

distinct temperatures and the values are compared using the graph.

From the above Fig. 4 it is noted that the kinematic viscosity for

distinct fluids reduces with increase in temperature. Kinematic

viscosity is more than all other liquids at a temperature of 30C for

ethylene glycol. The kinematic viscosity value is lowest for graphene-

based nanofluid at 30C and 80C compared to other samples. At

60C hybrid nanofluid showed least value of viscosity and CNT based

nanofluid showed higher value of kinematic viscosity at 80C

compared to other samples. From the result it can be concluded that

by the addition of CNT into the base fluid the viscosity value

increased slightly and by the addition of graphene into the base fluid

the velocity value slightly decreased.

By calculating the kinematic viscosity and density of the liquids,

the dynamic viscosity is determined. The values are plotted

graphically and compared to the suitable application fluid for heat

transfer. The values are as shown in Fig. 5. From the above chart it is

noted that with the rise in temperature, the dynamic viscosity of

distinct fluids reduces. At 30C CNT based nanofluid has the least

dynamic viscosity and ethylene glycol has the higher value. At 80C

the dynamic viscosity of graphene based nanofluid is lowest and

hybrid nanofluid has the highest value.

4.3. Heat Transfer Rate and Effectiveness

Double pipe heat exchanger is used to test the performance analysis

of nanofluid samples and base liquids. Two distinct combinations

such as parallel and counter flow are analyzed. Table 17 and Fig. 6

shows the experimental values for various fluid flow rates.

From the result it is observed that the heat transfer rate of base

fluid is enhanced by the addition of graphene and reduced by the

addition of CNT into the base fluid. The results revealed that the

effectiveness value in case of counter flow is maximum in

comparison with parallel flow. CNT based nanofluid exhibit the

higher value of effectiveness in case of counter flow arrangement.

The hybrid nanofluid exhibit highest value of effectiveness in parallel

flow arrangement. graphene based nanofluid showed increase in the

effectiveness value both in case of parallel and counter flow

arrangement compare to base fluid. The base fluid is having the least

value of effectiveness. From the result it is concluded that the

effectiveness and heat transfer rate will enhance by the addition of

nano particles into the base fluid.

5. Conclusions

The following conclusions can be drawn from the obtained results.

For the assessment of heat transfer rate and effectiveness, the

nanoparticles and the base liquids are chosen. The sonication

method prepares different samples of nanofluids and analyzes the

performance features using heat exchanger. Thermo-physical

characteristics tests are carried out on the prepared nanofluids. The

experiment findings indicate that in comparison with other

nanofluids and base liquids, the specific heat of graphene and hybrid

nanofluids is greater. The experiment concludes that base fluid's

cinematic viscosity is greater and that graphene-based nanofluid at

room temperature is smaller. Nanofluid and base fluid performance

analysis is conducted for parallel and counter flow setup with a

double pipe heat exchanger. From the outcomes, it is found that the

nanofluid based on carbon nanotube is much better than other

nanofluids and base fluid for counterflow structure. In contrast to

graphene-based nanofluid and base fluid, the hybrid nanofluid shows

much higher effectiveness for both parallel flow and counter flow

arrangements.

Fig. 4. Kinematic Viscosity values.

Fig. 5. Dynamic Viscocity values for different fluids.

Fig. 6. Effectiveness values of various fluids

Table 17. Heat transfer rate values for different fluids

Fluid

Heat Transfer Rate (J/s) Flow type

Parallel Counter

graphene based nanofluid

738.98 732.67

CNT based nanofluid

540.10 631.88

CNT + graphene based nanofluid

694.98 632.17

Distilled Water 653.11 709.62

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Ajey et al., Nano Progress

Nano Prog., (2021) 3(5), 47-52.

Conflicts of Interest

The authors declare no conflict of interest.

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