**Open Access**-
**Total Downloads**: 19 -
**Authors :**Lakshminarasimha. N , Dr. M. S. Rajagopal -
**Paper ID :**IJERTV8IS060478 -
**Volume & Issue :**Volume 08, Issue 06 (June 2019) -
**Published (First Online):**24-06-2019 -
**ISSN (Online) :**2278-0181 -
**Publisher Name :**IJERT -
**License:**This work is licensed under a Creative Commons Attribution 4.0 International License

#### Transient CFD Analysis of Different Cross-Section Fins Under Free-Convection Conditions

Lakshminarasimha. N1

1IGBC AP and Assistant Professor, Department of Mechanical Engineering, New Horizon College of Engineering, Bengaluru

Dr. M. S. Rajagopal2

2Professor and Chairman, Department of Mechanical Engineering,

Dayananda Sagar University, Bengaluru

Abstract- Manufacturers of aerospace and defense equipments are presently facing challenges related to both steady state and transient reliability of electronics systems; the continuing reduction in size of electronic components is resulting in higher power density due to which thermal management of electronic components is critical in electronic product development. Among heat transfer augmentation technique, passive cooling technique is more suitable than active cooling for specific applications. Also providing fins can regulate the temperature of the system at optimum levels by providing extended surface area of contact with surrounding cooling medium- air. In the present work, the Transient analysis has been carried out for three different cases to determine the transient performance considering different cross-sectional fins such as Tapered, Round and Rectangular configurations. The fins are subjected to free-convection cooling which are placed on plate with four heat sources each dissipating 100W power. Transient analysis is carried out using ANSYS CFD software for time step of 20 seconds and results obtained for different cross-section are compared for optimum temperature levels.

Keywords: Fins, Tapered fin, Round Fin, Rectangular Fin, Transient analysis, ANSYS CFD, Free-convection.

INTRODUCTION

To increase the heat transfer rates by increasing the surface heat transfer coefficient or increasing the temperature difference between surface and surrounding medium sometimes becomes impossible at particular condition and application; hence at that situation fins can be used for increasing the heat transfer rates from the surfaces [17].

Fins are classified as straight fins with uniform (Fig. 1.1) and non-uniform thickness (Fig. 1.2), annular fins (Fig. 1.3) and spine of constant cross-section (Fig. 1.4) and non- uniform cross section (Fig. 1.5).

Fig. 1.1 Fig. 1.2

Fig. 1.3 Fig. 1.4

Fig. 1.5

The knowledge of temperature distribution along the fin is necessary for proper design of fins. Hence in the present work, Transient analysis is carried out using ANSYS CFD for understanding the temperature distribution and heat flow from different cross-section fins such as Tapered, Round and Rectangular fins.

LITERATURE SURVEY

Literature survey is carried out to understand the state of art in CFD transient analysis on natural convection cooling of fins. Here are some literatures as discussed below:

Santosh Kansal et.al., [1], [2015], This paper deals with a comparative study using CFD on Electronic enclosure consisting fins of different configuration. The overall performance of the six different heat sinks with different shaped pin-fin structures was studied in this paper for different velocities varying from 5, 10 & 12 m/s. The paper presents simulation and thermal analysis of different shape fins heat sink for an electronic system cooled by natural convection.

Aartee. S. Lokhande, [2], [2018], this article gives overall review on work carried out on Transient analysis fins with different shapes and briefs some of technical details on fins.

Only major journals are discussed in this section, remaining journals, articles and textbooks listed in References.

METHODOLOGY

In the present work, Numerical approach is used to solve the conjugate heat transfer problem. Geometry, Meshing and Analysis are carried out using ANSYS CFD software. The details are given below.

Steps in the analysis involve:

Creation of Geometry

Meshing the Model

Apply Boundary Condition

Physical setup for analysis selecting appropriate Mathematical models

Result visualization and comparison

Geometry

The Geometry model of Tapered fin, Round fin and Rectangular fin is as shown in Fig. 3.1, Fig. 3.2 and Fig.

3.3. The fins are placed on a plate in an enclosure with Free-convection cooling. The plate is attached with four heat sources. The construction is maintained same for all the enclosures with different cross-section fins.

#### TOP VIEW SIDE VIEW

Fig. 3.2 Round fin model

Heat Source

#### ISO VIEW

Plate

Tapered Fin

Enclosure

Fig. 3.3 Rectangular fin model

Meshing

The cut plane mesh model of Tapered fin, Round fin and Rectangular fin is as shown in Fig. 3.4, Fig. 3.5 and Fig.

3.6. The Meshing parameters for three models are maintained same. The Models are meshed with Hexagonal elements.

Fig. 3.1 Tapered fin model

Fig. 3.4 Tapered fin meshed model

Fig. 3.5 Round fin meshed model

20 seconds is set for each heat sources which are with peak power of 100W. The variation of power is considered according to the equation of exponential curve [18], =

Ã— where a and b are constants and t is time. The flow is considered to be laminar and at Tranient condition.

MATHEMATICAL MODELS Conservation equations of mass and momentum for all flows are solved in ANSYS CFD and an additional equation for energy is solved for flows involving heat transfer. Flow inside a Electronic enclosure involves both fluid flow and fluid flow with heat transfer, hence governing equations [14] that are solved in ANSYS CFDare as listed below:

Mass conservation equation:

+. () = m

. (eqn. a) Momentum conservation equation:

() + . () = + . () + +

. (eqn. b)

Where, the stress tensor, is given by

= [ ( + T) 2 . ]

3

Energy conservation equation:

() + . (( + )) = . ( ) + Sh

Fig. 3.6 Rectangular fin meshed model

The convergence plot for the Meshed models is as shown in Fig. 3.7. The Residual monitor or convergence criteria for flow and energy are maintained to be 0.001 and 1e-7. Iteration per time step is set for 20 seconds.

Fig. 3.7 Mesh convergence plot

Solution Methodology

In the present analysis, the enclosure consist for four heat sources each dissipating 100W power, attached to a plate on which different cross-section fins are placed. The fins are subjected to free-convection cooling. The cycle time of

(eqn. c)

The above equations (a), (b) and (c) are a general form of governing equations and are valid for both compressible and incompressible flows.

RESULTS AND DISCUSSION

The velocity and temperature contours results obtained from the Transient analysis on different cross-section fins are discussed in this section. The temperature distribution results obtained for Tapered fin model is dicussed in section 5.1, Round fin model disscssed in 5.2 and Rectangular fin model is discussed in 5.3.

Temperature contours/distribution for Tapered fin model

Fig. 5.1(a)and (b) shows the Temperature contour for Tapered fin model at the time step of 20 second. The maximum temperature of 370C was found at the source. The heat conduction takes place through the thickness of plate from the source. The temperature distribution in detail at different time step is shown in Tabl 5.1 and Plot 5.1.

Fig. 5.1(a) Iso view of Tapered fin model

Time steps

Fin temperature in 0C

Source temperature 0C

0

20

20

1

20.0466

23.6988

2

20.1581

25.2468

3

20.3312

26.2739

4

20.5551

27.1116

5

20.8187

27.8589

6

21.1131

28.5558

7

21.432

29.2225

8

21.7709

29.8707

9

22.1267

30.5078

10

22.4974

31.1386

11

22.8813

31.7666

12

23.2773

32.3942

13

23.6848

33.0232

14

24.103

33.6553

15

24.5314

34.2915

16

24.9698

34.9329

17

25.4177

35.5803

18

25.8749

36.2345

19

26.3414

36.8961

20

26.8168

37.5658

Time steps

Fin temperature in 0C

Source temperature 0C

0

20

20

1

20.0466

23.6988

2

20.1581

25.2468

3

20.3312

26.2739

4

20.5551

27.1116

5

20.8187

27.8589

6

21.1131

28.5558

7

21.432

29.2225

8

21.7709

29.8707

9

22.1267

30.5078

10

22.4974

31.1386

11

22.8813

31.7666

12

23.2773

32.3942

13

23.6848

33.0232

14

24.103

33.6553

15

24.5314

34.2915

16

24.9698

34.9329

17

25.4177

35.5803

18

25.8749

36.2345

19

26.3414

36.8961

20

26.8168

37.5658

Fig. 5.1(b) Side view and Rear side view of plate attached to fin Table 5.1 Temperature distribution for Tapered fin at different time step

Plot 5.1 Temperature vs Time plot for Tapered fin

From the Table 5.1 and Plot 5.1, it is observed that the maximum temperature reached at time step of 20 second by fin was 26.810C and source was 37.560C.

Temperature contours/distribution for Round fin model Fig. 5.2 shows the Temperature contour for Round fin model at the time step of 20 second. The maximum temperature of 360C was found at the source. The heat conduction takes place through the thickness of plate from the source. The temperature distribution in detail at different time step is shown in Table 5.2 and Plot 5.2.

Fig. 5.2 Temperature contour of Round fin model

Table 5.2 Temperature distribution for Round fin at different time step

Time steps

Fin temperature in 0C

Source temperature 0C

0

20

20

1

20.0437

23.1916

2

20.1448

24.7165

3

20.2978

25.765

4

20.4919

26.6187

5

20.717

27.3703

6

20.9656

28.0602

7

21.2323

28.7102

8

21.5137

29.3336

9

21.8074

29.9389

10

22.1118

30.5321

11

22.426

31.1174

12

22.7494

31.698

13

23.0814

32.2762

14

23.4218

32.854

15

23.7703

33.4328

16

24.1267

34.014

17

24.491

34.5984

18

24.863

35.1871

19

25.2425

35.7809

20

25.6297

36.3803

Temperature contours/distribution for Rectangular fin model

Fig. 5.3 shows the Temperature contour for Rectangular fin model at the time step of 20 second. The maximum temperature of 360C was found at the source. The heat conduction takes place through the thickness of plate from the source. The temperature distribution in detail at different time step is shown in Table 5.3 and Plot 5.2.

Fig. 5.3 Temperature contour of Rectangular fin model

Table 5.3 Temperature distribution for Rectangular fin at different time step

Time steps

Fin temperature in 0C

Source temperature 0C

0

20

20

1

20.0437

23.1916

2

20.1448

24.7165

3

20.2978

25.765

4

20.4919

26.6187

5

20.717

27.3703

6

20.9656

28.0602

7

21.2323

28.7102

8

21.5137

29.3336

9

21.8074

29.9389

10

22.1118

30.5321

11

22.426

31.1174

12

22.7494

31.698

13

23.0814

32.2762

14

23.4218

32.854

15

23.7703

33.4328

16

24.1267

34.014

17

24.491

34.5984

18

24.863

35.1871

19

25.2425

35.7809

20

25.6297

36.3803

Comparing Table 5.2 and Table 5.3, the temperature distribution for Round fin and Rectangular fin is found to be same. Hence plotting the temperature distribution and is shown in plot 5.2.

Plot 5.2 Temperature vs Time plot for Round fin and Rectangular fin

Also the temperature distribution along the fin length is plotted for all the fin types and is as shown in plot 5.3. It is found that there is continuous reduction in temperature along the fin length.

Plot 5.3 Temperature vs. fin length plot

Comparing the Maximum temperature obtained for all the fin types, it is found that there is increase in temperature by 3% for Tapered fin compared to Round fin and Rectangular fin.

Velocity streamline plots

Fig. 5.4, Fig. 5.5 and Fig. 5.6 shows the velocity streamline plots for tapered fin, round fin and rectangular fin. The maximum velocity achieved through free-convection is 0.2 m/s.

Fig. 5.4 Streamline plot for Tapered fin

Fig. 5.5 Streamline plot for Round fin

Fig. 5.6 Streamline plot for Rectangular fin

Streamline plots helps in identifying and studying the circulation zones and flow around fins.

CONCLUSION

Transient analysis is carried out on Electronic enclosure using commercial CFD software ANSYS. The Transient analysis carried out for time step of 20 seconds on Electronic enclosure for three different cases consisting different cross-section fins such as Tapered fin, Round fin and Rectangular fin attached to a plate with four heat sources each dissipating power of 100W. Cooling of fins is through free-convection. The following are the conclusions drawn from the analysis results are:

In determining Temperature distribution at varied time step in carrying out transient analysis, CFD technique is very much effective at minimum time and cost.

Analysis is carried out for different cross- section fins for finding optimum temperature level. It was found that there is increase in temperature by 3% by using Tapered fin compared to Round fin and Rectangular fin and hence tapered are recommended.

The results obtained through the analysis helps as ready reckoner for beginning Engineers in decision making in selection of fins among different cross-sections and understanding temperature distribution in fins.

This work showcases determining transient performance of heat sink under natural convection conditions. Further work on varying pitch of the fins can be taken up to optimize the flow.

REFERENCES

Santosh Kansal, Piyush Laad, Performance and Thermal Analysis of Heat Sink with Fins of Different Configuration using CFD,International Journal of Scientific & Engineering Research, Volume 6, Issue 6, June 2015, ISSN 2229-5518

Aartee. S. Lokhande, Sachin Nimbulkar, Performance Analysis of Thermal Characteristics of Transient Heat Transfer through Finite Fins and Various shapes of Notches: A Review, International Journal of Research and Scientific Innovation (IJRSI) ,Volume V, Issue VIII, August 2018, ISSN 23212705

Kuang Yuan Kung and Shih-Ching Lo, Transient Analysis of Two- Dimensional Cylindrical Fin with Various Surface Heat effects, Research Article, Mechanical Engineering Department, Nanya Institute of Technology, Taiwan

Kuang Yuan Kung, Transient Analysis of Two- Dimensional Rectangular Fin with Various Surface Heat effects, Research Article, Mechanical Engineering Department, Nanya Institute of Technology, Taiwan

RASEELO J MOITSHEKIand CHARIS HARLEY,Transient heat transfer in longitudinal fins of various profiles with temperature- dependent thermal conductivity and heat transfer coefficient, Pramana- journal of physics, Indian Academy of Sciences, Volume 77, No. 3, September 2011, pp. 519-532

L. K. Sahoo, M. K. Roul, R. K. Swain, Computational Analysis of Natural Convection Heat Transfer from Pin Finned Plate,International Journal of Engineering Science Invention, National Conference On Recent Trends In Soft Computing & It Ã‚Â´s Applications (RTSCA-2K17), ISSN (Online): 2319 6734, ISSN (Print): 2319 6726,PP124-135

Dhanawade Hanamant S, K. N. Vijaykumar, Dhanawade Kavita, Natural convection heat transfer flow visualization of perforated fin arrays by CFD simulation, International Journal of Research in Engineering and Technology, Volume: 02 Issue: 12, Dec-2013,pp- 483-490, eISSN: 2319-1163 | pISSN: 2321-7308

Sumit Sharma, Devanshu Prasad, A Comparative Analysis of Natural convection between Horizontal and Vertical Heat sink using CFD, International Journal of Engineering Research and Technology, Vol. 4, Issue 06, June 2015, pp: 1089-1098,

ISSN: 2278-0181

A.A.WALUNJ, D.D.PALANDE,Experimental Analysis of Inclined Narrow Plate- Fins Heat sink under Natural Convection,IPASJ International Journal of Mechanical Engineering (IIJME), Volume 2, Issue 6, June 2014, pp: 8-13,

ISSN 2321-6441

K. Alawadhi, Abdulwahab J. Alsultan, S. Joshi, M. Sebzali, Esam. AM.Husain, Computational Fluid Dynamics (CFD) Analysis of Natural Convection of Convergent-Divergent Fins

in Marine Environments,Int. Journal of Engineering Research and Applications,Vol. 4, Issue 12 ( Part 1), December 2014, pp.32-36, ISSN : 2248-9622

Mahdi Fahiminia, Mohammad Mahdi Naserian, Hamid Reza Goshayeshi, Davood Majidian,Investigation of Natural Convection Heat Transfer Coefficient on Extended Vertical Base Plates,Energy and Power Engineering, 2011, 3, 174- 180doi:10.4236/epe.2011.32022 Published Online May 2011 (http://www.SciRP.org/journal/epe)

Lakshminarasimha N, Dr M S Rajagopal, CFD Analysis of Electronic Cabinet with High power devices and Fin heat sink,Journal of Engineering Research and Application, National Conference on Advances in Mechanical Engineering (NAME) 2018, ISSN : 2248-9622, PP 26-31

Lakshminarasimha N, Dr M S Rajagopal, Megaha Shukla, Numerical Investigation on Electronic Cabinet with interrupted Fin heat sink using CFD,International Journal of Scientific Research in Computer Science, Engineering and Information Technology, International Conference on New Horizons in Science Engineering Technology (NHSET-2018), Volume 4 | Issue 2, Published – 14 April 2018 | March-April- 2018 [ (4 ) 5 : 150-154 ], ISSN :2456-3307

ANSYS Fluent User Guide, Release 15.0, Nov. 2013 and ANSYS Fluent 12.0, Theory guide, April 2009

H K Versteeg and W Malalasekara, Computational Fluid Dynamics- Finite Volume Method, Text book of CFD, edition 1995

Yunus A Cengel, Heat Transfer- A Practical Approach,

Cooling of Electronic Equipment, Chapter 15

S. Domkundwar, S.C. Arora, A. V. Domkundwar, A course in Heat and Mass Transfer, Text book, Dhanpat Rai publications, Edition 2015

ANSYS Icepak Tutorials, Release 14.5, Oct. 2012