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International Journal for Modern Trends in Science and Technology Volume: 03, Issue No: 09, September 2017 ISSN: 2455-3778 http://www.ijmtst.com

CFD Analysis of Heat Pipe with Multiple Evaporators Bandaru Kanyakumari1 | P.Poornamohan2 1PG

Scholar, Department of Mechanical Engineering, Godavari Institute of Engineering and Technology, Rajahmundry, India.

2Senior Assistant Professor, Department of Mechanical Engineering, Godavari Institute of Engineering and Technology, Rajahmundry, India.

To Cite this Article Bandaru Kanyakumari and P.Poornamohan, “CFD Analysis of Heat Pipe with Multiple Evaporators”, International Journal for Modern Trends in Science and Technology, Vol. 03, Issue 09, September 2017, pp.-13-17.

ABSTRACT The size of electronic devices are decreasing day by day and throwing challenges on thermal engineers to find and invent better means to challenge heat dissipation rates. This led to give rise to my idea of getting this work on Heat pipe. Heat pipes are promising means to drive the heat from the electronic devise to the environment without using mechanical devices to operate the flow in it. The factors effects the performance of Heat pipe are geometry design, number of evaporators and condensers, working fluid selection, by coating different coatings to increase adhesive nature between inner wall of pipe and working fluid etc.,In this thesis, Heat Pipe System with multiple evaporators will be designed and modelled in 3D modelling software Pro/Engineer. Heat transfer characteristics will be determined by CFD and transient thermal analysis. CFD analysis will be done to determine the heat transfer rate, pressure drop, mass flow rate, heat transfer coefficient with R134 and R410 as the working fluid. Transient thermal analysis will be done to determine heat transfer rate and temperature distribution Keywords: Heat pipe, multiple evaporators Copyright © 2017 International Journal for Modern Trends in Science and Technology All rights reserved.

I. INTRODUCTION A heat pipe is a heat-transfer device that combines the principle of both thermal conductivity and phase transition to efficiently manage the transfer of heat between two solid interfaces. At the hot interface of a heat pipe a liquid in contact with a thermally conductive solid surface turns into a vapour by absorbing heat from that surface. The vapor that travels along the heat pipe goes to the cold interface and condenses back into a liquid releasing the latent heat. The liquid then returns to the hot interface through capillary action, centrifugal force, or gravity, and the cycle repeats. Due to the very high heat transfer

coefficients for boiling and condensation, heat pipes are highly effective thermal conductors. The effective thermal conductivity varies with heat pipe length, and can approach 100 kw/(m-k) for long heat pipes, in comparison with approximately 0.4 kw/(m-k) for copper.

Figure 1: Traditional heat pipe

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Bandaru Kanyakumari and P.Poornamohan : CFD Analysis of Heat Pipe with Multiple Evaporators II.

WORKING PRINCIPAL OF HEAT PIPE

Conventional heat pipe is a heat transfer device which is capable of carrying the large amounts of heat using the small temperature differences. The tube is completely emptied by removing the foreign particles and then it is filled by the working fluid which is sufficient to saturate wick structure.

Pressure in tube is equal to saturation pressure, which is connected to heat pipe temperature. When heat is entering the evaporator, the equilibrium will be disturbed, thereby producing steam having a slight higher pressure and temperature. The high pressure of the vapour causes it to flow along the tube to the condenser, where a slight lower temperature causes the vapour to condense and releases its latent heat of vaporization. The condensed fluid is then impelled back to the evaporator because of the forces develop due to capillary actions created in the wick.

III.

EXPERIMENTAL MODEL

The geometry of heat pipe is designed by using CATIA software. Total length of heat pipe is 900mm with 100mm evaporator section, adiabatic section with 270mm and 530mm of condenser section. The inner pipe diameter is 15.9mm and thickness 1.6mm, the outer pipe diameter is 53mm and thickness 2mm.

Figure 2: Design Of Heat Pipe

IV.

alone system ( geometry import geometrybrowseselect geometryok) d) Now double click on mesh Select the faces which are to be named as inlet and outlets (Select face left click  named selection  specify name [inlet outlet]  ok Also specify any other required named selections (ex: fine surface, inner face etc.) e) Now go to mesh in left side of the graphic window, select mesh size and click update in the tool bar above graphic window f) Now double click on set up, a window pops up (fluent launcher), click ok, fluent window opens. g) Now go to solution setup general click check and report quality one after another ANSYS checks the geometry and reports orthogonal quality and aspect ratio h) Go to models, select energy  click edit select on  ok i) Click material  select required fluid and solid material from fluent database or enter required materials manually using create/edit button j) Select cell zone conditions and specify cell zone conditions (solid/fluid) k) Select boundary conditions to specify the boundary condition Boundary conditions zone  edit  enter boundary conditions (velocity and pressure for inlet and outlet, convection, conduction, temperature etc. for walls) l) Select solution initialization  hybrid initializationinitialize and wait for the following massage: hybrid initialization is done. m) Select run calculationsenter number of iterations (100)  enter reporting interval(1)  profile update interval hit calculate and wait until iterations complete n) Retrieve results from results module.

METHODOLOGY

The main objective of this experimentation wasto estimate the effect of increasing number of evaporators with different working fluids in heat pipeand also to determine the effect of adiabatic section in total heat transfer rate. a) Open ANSYS workbench 15.0 b) Drag and drop fluid flow (fluent) from analysis system in to project schematics to create a standalone system c) Now import a geometry saved in .igs file format by left clicking on the geometry in the stand 14 International Journal for Modern Trends in Science and Technology

Bandaru Kanyakumari and P.Poornamohan : CFD Analysis of Heat Pipe with Multiple Evaporators BOUNDARY CONDITIONS:

Condenser condition : mode of heat transfer convection and heat transfer coefficient is 13.3w/m2k inlet and temperature at condenser is 300k and wall thickness is 0.001m. Evaporator condition: temperature at evaporator is 348.5k and wall thickness is 0.001m.

PROPERTIES OF FLUENT MATERIALS:

The fluent materials which are taken for analysis are copper, R134a and R410a.copper is used taken as heat pipe material and working fluids are R134a, R410a.The properties of fluent materials are shown in below table.

Material NAME

Density Kg/m3

Specific Heat J/kg-k

COPPER (solid)

8960

376.8

R134a (fluid)

3

840

R410a (fluid)

3.734

905.2

Thermal conductivity W/m-k

Viscosity Kg/m-s

385

_

0.013 16.5 0.01638

13.36

V. RESULT AND DISCUSSION Velocity vectors colored by total temperature (K)

Basic model with 1 evaporator (R134a) Total Heat Transfer Rate (w) ---------------------------------------------------Adiabatic 0.37188333 Condenser -0.16767849 Contact_region-src 0 Contact_region-trg 0 Contact_region_2-src 0 Contact_region_2-trg 0 Evaporator 5.0332098 inlet_ 88.011452 Outlet -93.249992 Wall-21 0 Wall-22 0

Wall-24 0 Wall-25 0 Wall-part_1 0 Wall-part_2 0 Wall-part_3 0 ------------------------------------------------------Net -0.0011260062 Basic model with 5 evaporators (R134a) at variable thermal conditions Total Heat Transfer Rate (w) -------------------------------- -------------------adiabatic_ 0.18945971 condencer_ -0.59824055 contact_region-src 0 contact_region-trg 0 contact_region_2-src 0 contact_region_2-trg 0 contact_region_3-src 0 contact_region_3-trg 0 contact_region_4-src 0 contact_region_4-trg 0 contact_region_5-src 0 contact_region_5-trg 0 contact_region_6-src 0 contact_region_6-trg 0 evaporator_s1 5.0330677 evaporator_s2 4.4616117 evaporator_s3 3.8960066 evaporator_s4 3.3361003 evaporator_s5 2.7822862 inlet 88.011444 outlet -107.12292 wall-45 0 wall-46 0 wall-48 0 wall-49 0 wall-51 0 wall-52 0 wall-54 0 wall-55 0 wall-57 0 wall-58 0 wall-60 0 wall-61 0 wall-part_1 0 wall-part_2 0 wall-part_3 0 wall-part_4 0 wall-part_5 0 wall-part_6 0 wall-part_7 0 ---------------- -------------------Net -0.011181384

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Bandaru Kanyakumari and P.Poornamohan : CFD Analysis of Heat Pipe with Multiple Evaporators Tabular report of heat pipe with R134a as Working fluids with single condenser and multiple evaporators with evaporators at variable temperatures R134a with variab le evapor ator tempe rature with 1 evapor ator with 2 evapor ator with 3 evapor ator with 4 evapor ator with 5 evapor ator

Total pressure(pa)

Total temperature( K)

Wall shear stress(pa)

min

min

min

max

max

max

4.38 E+03

1.89 E+06

3.00 E+02

3.01 E+02

0.00 E+00

3.80 E+04

4.38 E+03

2.13 E+06

3.00 E+02

3.01 E+02

0.00 E+00

3.80 E+04

4.38 E+03

2.38 E+06

3.00 E+02

3.02 E+02

0.00 E+00

3.80 E+04

4.38 E+03

2.62 E+06

3.00 E+02

3.02 E+02

0.00 E+00

3.80 E+04

4.38 E+03

2.87 E+06

3.00 E+02

3.03 E+02

0.00 E+00

3.80 E+04

Total heat tran sfer rate( W)

0.00 113 -0.0 043 8 -0.0 049 8 -0.0 109 2 -0.0 111 8

nsers

1 evapo rator and 1 conde nser 1 evapo rator and 2 conde nsers 1 evapo rator and 3 conde nsers

min

sfer rate W

max

min

max

min

max

4.38 E+03

1.89 E+06

3.00 E+02

3.01 E+02

0.00 E+00

3.80 E+04

0.00 113

4.38 E+03

3.19 E+06

3.00 E+02

3.01 E+02

0.00 E+00

3.80 E+04

0.00 224

4.39 E+03

4.49 E+06

3.00 E+02

3.01 E+02

0.00 E+00

3.80 E+04

-0.0 0173

Report of heat pipe with R134a as Working fluids with single condenser and multiple evaporators with evaporators at variable temperatures

Total pressure Tabular report of heat pipe with R134a as Working fluids with multiple condenser and multiple evaporators With Multipl e conden sers

1 Evapor ator and 1 Conde nser 3Evap orators and 2 Conde nsers 5Evap orators and 3 Conde nsers

Total pressure(pa)

Total temperature k

Wall shear stress pa

min

min

min

4.38 E+03

max

1.89 E+06

3.00 E+02

max

3.01 E+02

0.00 E+00

max

3.80 E+04

Tota l heat tran sfer rate W -0.0 011 3

4.38 E+03

3.68 E+06

3.00 E+02

3.02 E+02

0.00 E+00

3.80 E+04

-0.0 108 5

4.39 E+03

5.47 E+06

3.00 E+02

3.03 E+02

0.00 E+00

3.80 E+04

-0.0 173 1

2.00E+06 0.00E+00

with 1 evaporator with 2 evaporator with 3 evaporator with 4 evaporator with 5 evaporator Total pressure min Total pressure max

R134a with variable evaporator temperature (total pressure)

Total temperature 3.04E+02 3.02E+02 3.00E+02 2.98E+02

Total temperature min Total temperature max

Table: 5.6 Tabular report of heat pipe with R134a as Working fluids with multiple condenser and single evaporators Multi ple conde

4.00E+06

Total pressure(pa)

Total temperature k

Wall shear stress pa

R134a with variable evaporator temperature (total temperature)

Total heat tran

16 International Journal for Modern Trends in Science and Technology

Bandaru Kanyakumari and P.Poornamohan : CFD Analysis of Heat Pipe with Multiple Evaporators

Total heat transfer rate 0

Proceedings of the 34th InternationalConference on Environmental Systems,” (ICES), SAE 2000-01-2316.

-0.002 -0.004 -0.006 -0.008 -0.01

-0.012 Total heat transfer rate

VI. CONCLUSION The results obtained can be studied and concluded that when multiple evaporators are used instead of single evaporators the heat that can be carried away from the heating element is appreciably increased and thus this arrangement yielded better results when compared with single evaporator set-up. In the next phase of my project if we use R134a instead of R410 a the temperature that is carried away by the fluid will be a added advantage in this project. Hence finally the setup with multiple evaporators with R134a fluid is better combination which improved heat transfer rate in a heat pipe.

REFERENCES [1] HEAT PIPES: REVIEW, OPPORTUNITIES AND CHALLENGE SamirFaghri [2] TRANSIENT MODELING OF HYBRID LOOP HEAT PIPE SYSTEMS WITH MULTIPLE EVAPORATORS DmitryKhrustalev [3] Design Aspects to Improve the Cooling Efficiency of Equipments Using Miniature Loop Heat Pipe: A Literature [4] Characteristics of Heat Transfer for Heat Pipe and Its CorrelationAloke Kumar Mozumder, Mohammed Sha�ulHasibChowdhury [5] ADVANCED HYBRID COOLING LOOP TECHNOLOGY FOR HIGH PERFORMANCE THERMAL MANAGEMENTChanwoo Park and AparnaVallury [6] Bugby, D.C., 2007, “Multi-Evaporator Hybrid Two-Phase Loop Cooling System for Small Satellites” Proceedings of Small SatelliteConference, Space Dynamics Laboratory, Logan, Utah.

[7] Cullimore, B., and Bauman, J., 2000, “Steady State and Transient Loop Heat Pipe Modeling,”

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