Thermal Management of Solar Power Pack using Computational … · 2019-07-01 · Thermal Management...

Thermal Management of Solar Power Packusing Computational Fluid Dynamics

Lakshminarasimha N 1

1PG Student, Thermal Engg.Department of Mechanical Engg.

Dr. M.S. Rajagopal 2

2Professor & HeadDepartment of Mechanical Engg.

M. Vedavyasa 3

3Associate ProfessorDepartment of Mechanical Engg.

Global Academy of TechnologyBangalore, India



Abstract— Solar Power Pack (SPP) is anenclosure which houses heat generatingelectrical devices such as Battery Bank, Inverterand Controller. The present study involvescooling and ventilation analysis of the enclosuresuch that the electrical components operate atless than their limiting temperatures. Further,optimization studies are also carried out todetermine fan location and locations of inlet andexit vents besides positioning of Baffles foruniform air motion. This study will also help inminimizing the pumping power cost bydetermining the pressure losses. ThermalManagement of SPP has been carried out usingCFD software ANSYS Workbench- FLUENTfor both 2D and 3D geometry. Numerical resultsobtained from FLUENT agree well withanalytical results.

Keywords-- Thermal Management, Solar PowerPack, Enclosure, CFD, Optimization, FLUENT,Cooling, Ventilation

Terminology--L = Length of SPPW = Width of SPPH = Height of SPPLb = Location of Battery BankLC = Location of ControllerLi = Location of InverterLf = Location of exhaust fanLV = Location of inlet vent2D = Two-dimensional3D = Three-dimensionalTSA = Total surface areaCFM = Cubic feet per minute

1. INTRODUCTION

In today’s climate of growing energy needs andincreasing environmental concern, alternatives touse of non-renewable and polluting fossil fuelshave to be invested. One such alternative is solarenergy. Solar power is the conversion of sunlight

into electricity directly using photovoltaics. Thelatest and the most cost effective method forintegrating solar power tohomes/offices/colleges/rural electrification etc. arethrough the use of Solar Power Pack. Present workis generic and can be used as preliminary literaturefor studying any different kinds of Solar PowerPack models.

Internal flow and thermal analysis in an enclosurecontaining heat generating equipments is always achallenge in the field of Heat transfer. Due to highexpense of experimental study in recent years,Computational Fluid Dynamics (CFD) is graduallybecoming the most efficient tool in thermalenclosure design. Study of Solar Power Packcomprises of; overall evaluation of designinvolving ventilation and cooling, study of velocityand temperature contours and optimization ofdesign such as; fan size and location, location andsize of inlet and exit vents and positioning ofBaffles for uniform air motion. Also compute themany derived parameters along with the graphicalrepresentation of the interested regions. The mainobjective of the present work is to undertake anumerical investigation to evaluate the thermaldesign of SPP and further optimize the design tominimize the cost using simple 2D & 3D models.

2. LITERATURE SURVEY

In this section, literature survey has been conductedto understand the state of the art in thermalmanagement of Solar Power Packs in particular andCFD in general to know the appropriate boundaryconditions, modeling of heat sources and variousCFD models. The summaries of most importantpapers are listed below.

Hoffman- A Pentair Company [1], [2003], releasedtechnical information data sheet on heat dissipationin an electrical enclosure. This technical data/cutsheet is majorly for electrical enclosures exposed tooutdoor conditions. The technical informationhighlights majorly about, Enclosures temperature

International Journal of Engineering Research & Technology (IJERT)

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NCERAME - 2015 Conference Proceedings

Volume 3, Issue 17

Special Issue - 2015

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rise/ Determination of temperature rise for anenclosure, Evaluation of solar heat gain andSelection of fans as per cooling requirement for anenclosure. Hence this manual is highly helpful inpreliminary design stage, in predicting the coolingrequirements for electronic and electricalenclosures.

Bud Industries, Inc., [2], [2007], released technicaldata hand book on Enclosure design tips. Thisguide helps in selecting cabinets, enclosures andother packaging system for electronic products.Also this booklet summarizes some of the moreimportant issues of packaging for electronicsystems and products, with the goal of helping usevaluate our options quickly, and then selecting theoptimum solution for our application. As perproject concerned the booklet majorly highlightsabout Materials and finishes for an enclosure andBasics of cooling for cooling requirement in anenclosure.

Mahendra Wankhede, et al., [3], [2010], Papercomprises study on evaluation of cooling solutionsfor outdoor electronics. Both experimental andCFD simulation had been carried out for threedifferent conFig.urations of enclosures including asolar radiation shield, double-wall enclosure and aair-to-air heat exchanger; using a typicalAluminium enclosure. Each enclosure wasconsisting 100W generating PCBs. The workshowed that solar heat load can increase theinternal air temperature by 20%, White coating ofan enclosure reduces internal air temperature byaround 25% and as the major part of the workhighlighted that 50-55% can reduce ∆T due to theinternal fans compared to a sealed enclosure withno fans and having radiation shield and double-walled enclosure with air circulation providedmodest improvements of around 25%, where as air-to-air heat exchanger showed improvement by75%.

Tom Kowalski and Amir Radmehr, [4], This Paperhighlights the significance of using coupled FNMand CFD based analysis in cooling of electronicenclosure. The study demonstrates the applicationof coupled Fluid Network Method (FNM) and CFDin the analysis of flow behavior and Thermalbehavior in a telecommunication cabinet. Thecabinet is forced- flow air cooled consisting a stackof PCB’s. The work showed detailed measurementof airflow velocities in various parts of the cabinet,the predicted variation of the flow rates throughcard passages and total flow through system werefound to be within 10% of their experimentallymeasured values.

It is observed that very few literatures are availableon thermal management of SPP using CFD thoughthermal analysis at PCB and chip level is available.However, industrial data sheets are available asready reckoner to help designers to choose the rightsize of fan and number of fans. This study is aimedat optimizing the cooling and ventilationparameters to have better understanding of thesystem.

3. METHODOLOGY

The analysis of SPP is been carried out usingCommercial CFD code ANSYS Workbench-FLUENT and Modeling and Meshing for 3D SPPenclosure were carried out in ANSYS ICEPAK.

Fig. 1: Combined module of CFD code

ANSYS Workbench delivers innovative, dramaticsimulation technology advances in every majorphysics discipline, along with improvements incomputing speed and enhancement to enablingtechnologies such as geometry handling, meshingand post-processing (Fig. 1). These advancementsalone represent a major step ahead on the pathforward in Simulation driven ProductDevelopment.ANSYS ICEPAK provides highly simplified wayof modeling and meshing for cubical electronicenclosure problems.

3.1 GEOMETRY

The Geometry of SPP consists of Battery Bank,Inverter, Controller, and Inlet vent andoutlet/exhaust fan. The most important thing to benoted is that the geometry is planar symmetry. Thedimensions specified for the models below in 3.1.1and 3.1.2 are elaborated in the above terminology.

ANSYS WORKBENCH

Geometryusing design

modeller

MeshingusingICEM

Boundarycondition, solver &

postprocesssingusing FLUENT

Combination of


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Fig. 2: 2D SPP Model

Fig. 2, shows the 2D cut plane (XY plane- rightbottom corner of Fig. 2) taken from planarsymmetry 3D model which has been considered for2D analysis. A simplified 2D analysis is carried outat the mid-plane of SPP to get an insight of thephysics of the problem though this model doesn’tcapture the overall objective of determination ofaccurate flow and temperature distributions. 2-Dgeometry does not accurately capture locations ofinlet vent, fan location and heat generating devices.

3.1.2 3D Geometry model

The planar symmetry 3D SPP domain withdimensions as per above terminology is shown inFig. 3. The 3D model captures the problemobjective and fetches us real results and provides usthe clear visualization of contours and vectors atour interested spots in the domain.

Fig. 3: 3D SPP Model

3.2 MESHING

Meshing is the important criteria as part of analysisconsidered. Maximum time spent in meshing is thetime well spent. Mesh independence studies havebeen carried out for both 2D and 3D domainmeshes. The details of meshing for 2D and 3Ddomain are as described below.

3.2.1 2D Meshing

The 2D mapped fine mesh is shown in Fig. 4. Meshindependence study graphs for the 2D mesh areshown in Fig. 5 and Fig. 6. Based on this study,further analyses are carried out for Quad mesh with46280 elements and 47204 nodes. The convergencecriteria for the continuity, x-velocity, y-velocity,energy, k and epsilon are shown in Fig. 7.

Fig. 4: 2D Mesh

H

L

3.1.1 2D Geometry model


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Fig. 5: 2D Mesh independence plot for Maximum Velocity vs.Mesh elements

Fig. 6: 2D Mesh independence plot for Maximum Temperaturevs. Mesh elements

Fig. 7: 2D Mesh Convergence criteria

3.2.2 3D MESHING

Creating a 3D mapped hexahedral mesh is a bigchallenge; however Icepak provides an easyplatform to create mapped hexahedral mesh forcubical geometries. Icepak also facilitates fluid andsolid surface extractions which can be namedappropriately. Icepak is used for modeling &meshing process & the mesh has been transferredto fluent for further analysis.

Mesh independence study graphs for the 3D meshare shown in Fig. 9 & Fig. 10. The study showsthat mesh with 272786 elements and 284868 nodes

is the optimum mesh which is shown in Fig. 8. Theconvergence criteria trends for the continuity, x-velocity, y-velocity, z-velocity energy, k andepsilon are shown in Fig. 11.

Fig. 8: 3D Mesh

Fig. 9: 3D Mesh independence plot for Maximum Velocity vs.Mesh elements

Fig. 10: 3D Mesh independence plot for Maximum Temperaturevs. Mesh elements

6.445

6.45

6.455

6.46

6.465

32144 46280 52560

Max

. vel

ocit

y (m

/s)

Mesh independence chartMax. Velocity vs. Mesh elements

Max.velocity(m/s)

327.5328

328.5329

329.5

Max

. tem

pera

ture

(K)

Mesh independence chartMax. Temp vs. Mesh elements

max.temperature(k)

55.25.45.65.8

66.26.46.6

Max

. Vel

ocut

y (m

/s)

Number of mesh elements

Max Velocity(V)

4041424344454647

3942

4

8024

9

1570

05

2727

86

4161

74

1059

528

Max

Tem

p (d

eg. C

)

Number of mesh elements

Maxtemperature(T)


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Fig. 11: 3D Mesh Convergence criteria

3.3 SOLUTION METHODOLOGY

In the present investigation, the enclosure exhaustfan of 285 CFM has been selected throughanalytical calculation [1]. Flow is considered to beincompressible and steady. The internal flow isgoverned by Reynolds Average Navier-Stokesequations (RANS). Standard K-epsilon model isused to solve the flow analysis. The heat generatingsources wall are at heat flux and no slip condition.Standard K-epsilon model comes under twoequation model of turbulence kinetic energy k andits dissipation rate ϵ & hence these two equationsare solved for obtaining the result. The incomingair through inlet vent is due to negative pressureoccurred & removing heat through exhaust fan.Transport equation for momentum and turbulenceparameter is solved with SIMPLE discretizationscheme.

3.4 MATHEMATICAL MODELS

Conservation equations of mass and momentum forall flows are solved in ANSYS FLUENT and anadditional equation for energy is solved for flowsinvolving heat transfer. Flow inside a Solar PowerPack involves both fluid flow and fluid flow withheat transfer, hence governing equations [8] that aresolved in FLUENT are as listed below:

Mass conservation equation:

+ ∇. ( ⃗) = m

Momentum conservation equation:( ⃗) + ∇ . ( ⃗ ⃗) = −∇ + ∇ . ( ̅) + ⃗ +Where, the stress tensor, is given by̅ = [ (∇ ⃗ + ∇ ⃗T)− ∇ . ⃗ ]Energy conservation equation:( ) + ∇ . ⃗ ( + ) = − ∇ . (∑ ℎ ) + Sh

The above equations are a general form ofgoverning equations [8] and are valid for both

compressible and incompressible flows. Thegoverning equations with no time derivative termstates steady flow.Also additional transport equations as shownbelow, need to be solved since flow is turbulent.The turbulence model used for this analysis isStandard k- ∈ Turbulence model.( ) + ( )= + ++ − − +And( ) + ( )= ++ ( + )− +Where, turbulent or eddy viscosity, =and Gk & Gb represents the generation ofturbulence kinetic energy due to mean velocitygradients and buoyancy. YM represents thecontribution of the fluctuating dilation incompressible turbulence to the overall dissipationrate.Here, the model constants C ∈, C ∈, Cμ, σ , and σϵhave the following default values as below:C ∈ = 1.44 , C ∈ = 1.92 , Cμ = 0.09, σ = 1.0 ,σϵ = 1.3All the above mathematical models cannot besolved by analytical method for complex flows.Hence all these equations are solved usingFLUENT. Further in-depth details regardingmathematical models can be referred in FLUENT-Theory guide [8].

3.5 RESULTS AND DISCUSSION

3.5.1 2D RESULTS

It is stated in section 3.1.1, that the 2D analysisdoes not capture the overall problem objective butthe main purpose of 2D analysis is to studydifferent solver options, different Boundaryconditions and effect of critical geometricparameters and understanding the velocity,pressure and temperature contours.Figures shown below are the velocity (Fig. 12) andtemperature contours (Fig. 13) for the SPPenclosure.


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Fig. 12: Velocity contour for 2D domain

Fig. 13: Temperature contour for 2D domain

Maximum Velocity(m/s)

6.46

Maximum Temperature(℃)

57

Enclosure fluidTemperature rise (∆T)

in (℃)

0.809

Table 1: 2D analysis results

Table-1 shows the results obtained from 2Danalysis. Maximum temperature is found at the topsurface of the Battery Bank and maximum velocityobviously near inlet and outlet. The locations ofBattery Bank, Inverter and Controller are actual in3D, where as in 2D their locations cannot becaptured accurately, since 2D mid x-y plane is

considered. Further, locations of fan inlet and outletvents are also approximate. Thus the results areexpectedly not accurate, but certainly provide aninsight of complex coupled flow and heat transferproblem.

3.5.2 3D RESULTS

3.5.2a. Velocity contours and Temperaturecontours

Fig. 14: Velocity contour for 3D domain

Fig. 15: Temperature contour for 3D domain

Maximum Velocity (m/s) 6.0Maximum Temperature

(℃)42.5

Enclosure fluidTemperature rise (∆T) in

(℃)

4

Table 2: 3D analysis results


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Figures 14 & 15 show the velocity and temperaturecontours in 3D domain. The temperature contoursnear the Battery is shown in Fig. 16 and near theInverter and Controller in Fig. 17. The maximumtemperatures at the Inverter, Battery and Controllerare shown in table-3. Though the overall velocitydistribution is relatively uniform, the flows arerelatively lesser at the Inverter resulting in highertemperature. Hence flows need to be optimizedsuch that the temperatures of the devices areuniform.

Fig. 16: Temperature in Battery

Fig. 17: Temperature in Inverter and Controller

Heat generatingdevices

Temperature obtainedin℃

Battery 39Inverter 42.5

Controller 34.61

Table 3: Temperature of Heat generating devices

Table-2 shows the maximum velocity andtemperatures in 3D analysis. Comparison of Table-1 and Table-2, show that there is considerabledifference in the values of maximum temperature,maximum velocity and temperature difference offluid temperature. This is expected since 2-D and3-D geometries are different.

The velocity stream line plot is as shown in Fig. 18.

Fig. 18: Velocity stream line plot

From the stream line plot it is quite clear that theflow is channeled in all four directions (Top, right,left & bottom) and the most predominant flowbeing in the top direction. Considering this there isscope to optimize the flow and a suitable Baffle atthe right position can be provided to direct more airtowards the Inverter. These are discussed in section3.5.2c. Further the locations of inlet and outlet alsoare studied in section 3.5.2b to understand its effecton temperature distribution.

3.5.2b. Optimization of the location of inlet-ventand exhaust fan

Two different locations for the inlet vent have beenstudied (Fig. 19) and the results are shown inTable-4


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Fig. 19: Inlet-vent optimization

Devices Temperature in℃ for inletlocation-1

Temperature in℃ for inletlocation-2

Battery 39 37.64Inverter 42.5 47

Controller 34.61 38.2

Table 4: Results obtained by optimizing the location of inletvent

Changing the location of inlet vent from location-1to location-2, the Battery temperature is reducedbut the temperatures of Inverter and Controllerhave increased. Hence location-1 is optimum.Similarly, effect of two different outlet locations ontemperatures has also been carried out (Fig. 20). Itis found that there was no considerable change inthe temperatures of heat devices. For location-2,the distance between inlet to exhaust fan is lessercompared to location-1 and considerable amount ofair escapes without cooling the heating devices.And hence is not preferred.

Fig. 20: Optimization of exhaust fan

3.5.2c. Positioning of Baffle

As stated in section 3.5.2a, the flow is predominantin top direction, hence decided to provide Baffle atposition-1 and position-2.In the first analysis, Baffles without perforation are

provided near the inlet to direct more air towardsthe Inverter (Fig. 21). Fig.22 gives the comparisonof temperatures of heat devices. It is observed thatposition-2 is better since the maximum temperaturein all devices is limited to 38℃.

Fig. 21: Positioning of Baffle with no perforated vents

Fig. 22: Devices temperature at different Baffle position forBaffle with no perforated vents

In the next analysis, perforated Baffles withrectangular holes are provided at position 2 asshown in Fig. 23. The openings provided on theBaffle are 50% of the total area of the Baffle.















34.535

35.536

36.537

37.538

38.539

39.5

Tem

pera

ture

in d

eg.C

Devices

Devices temperature at different baffleposition for baffle with no perforated vents















Devices temperature at different baffleposition for baffle with no perforated vents

Temperature forBaffle position-1

Temperature forBaffle position-2


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Fig. 23: SPP with Baffle with perforated rectangular vents

Fig. 24 shows the comparison results for threedifferent cases viz. i. With no Baffle ii. Baffle withno vents iii. Baffle with rectangular vents. It isevident that results are better with Baffle comparedto the case without Baffles. In the cases withBaffles, Baffle without vents gives reducedtemperatures but with increased pressure drops.

3.5.2d. Pressure losses and Pumping power cost

Pressure drop is directly proportional to thePumping power. Among the various cases studied,pressure losses are minimum for the case withoutBaffle and case with Baffle having rectangularvents though the later is having slightly lesserpressure drop (Fig. 24). It is obvious that Bafflesresult is higher drops at the entry, but pressurelosses further downstream are also important. Ingeneral when the ventilation design is void ofconstrictions, pressure losses can be reduced whichis also evident from CFD results. However, CFDplays a major role in determining the exactpressure drops which will be very useful to thedesigner.

Fig. 24: Comparison graph for Temperature and Pressure dropfor SPP with Baffle & with no Baffle

3.6 COMPARISON OF RESULTS WITHANALYTICAL RESULTS

Considering flow to be incompressible and steady,Applying simple mass balance i.e. flow at inlet =flow at outlet. Since same areas provided at bothinlet and outlet, the velocity at both inlet and outletshould be 6.0 m/s as per manual calculations. It isobserved to be same from CFD as well. This isapplicable for both 2-D & 3-D cases.Similarly, considering heat balance, the heatdissipated by the heat devices should be equal toheat carried away by the fluid. This is verified inboth 2-D & 3-D cases.2-D case:Fluid temperature rise by analytical method: 0.88℃Fluid temperature rise by CFD: 0.809℃3-D case:Fluid temperature rise by analytical method: 4.0℃Fluid temperature rise by CFD: 4.0℃Thus it is evident that the CFD results are justifiedas both mass and heat balances are maintained.

3.7 CONCLUSIONS

The following conclusions can be drawn based onCFD analysis carried out on Solar Power Pack(SPP) enclosure consisting Battery Bank, Inverterand Controller.1, CFD is very powerful tool to determine the exactpressure drops, maximum velocities andtemperatures.2. CFD also provides insight of the cooling andventilation problem, by determining velocity andtemperature distributions. This will help thedesigner.








3.7 CONCLUSIONS


05

1015202530354045

Bat

tery

Inve

rter

Con

trol

ler

Pres

sure

dro

p

Bat

tery

Inve

rter

With no Baffle Baffle with noperforated vents at

position-2

Enclosure Pressure drop & Devicestemperature for different SPP analysis type








3.7 CONCLUSIONS


Con

trol

ler

Pres

sure

dro

p

Bat

tery

Inve

rter

Con

trol

ler

Pres

sure

dro

p

Baffle with noperforated vents at

position-2

Baffle withrectangular

perforated vents atposition-2

Enclosure Pressure drop & Devicestemperature for different SPP analysis type


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3. Parametric studies have been carried out tounderstand the effect of following parameters:3.1 Location of Inlet vent3.2 Location of exhaust fan (outlet vent)3.3 Provision of Baffles3.4 Effect of Baffles with and without vents4. It can be concluded that for minimizingtemperatures, Baffles without vents arerecommended though there is a higher pressuredrop.5. Considering both temperature and pressure drop,Baffle with rectangular holes is recommended.It must be concluded that the present study is by nomeans exhaustive and there is further scope foroptimization. However, the CFD results are veryuseful to the designer and these results will helphim to make decisions faster. Further, they will aidin preparing a ready reckoner for cooling andventilation design.

ACKNOWLEDGMENT

We would like to thank the Global Academy ofTechnology college management and Departmentof Mechanical Engineering, (VTU ResearchCentre) for providing us the facility to successfullycomplete this project and encouraging us inpublishing paper. We also thank M/s. SunEdisonfor providing data at critical junctures and theiroverall support.

REFERENCES

[1] Hoffman- A Pentair Company, “Heat dissipation in Electrical

enclosure”, “Technical information on Thermal Management of Electrical enclosures”, ©2003 Hoffman Enclosures Inc.

[2] Bud Industries, Inc., “Enclosure Design Tips Handbook”,

July 2007,

© Bud Industries Inc.

[3] Mahendra Wankhede, Vivek Khaire, Dr. Avijit Goswami and

Prof. S. D. Mahajan, “Evaluation of cooling solutions for outdoor electronics”, Journal on electronics cooling from

electronics-cooling.com, Volume 16, No. 3, Fall2010

[4] Tom Kowalski and Amir Radmehr, “Thermal Analysis of an

Electronics Enclosure: Coupling Flow Network Modeling

(FNM) and Computational Fluid Dynamics (CFD)”, no

details

[5] Süddeutscher Verlag onpact (Rittal GmbH & Co. KG), “Project Planning Manual: Enclosure Heat Dissipation”, ©

2009 by Süddeutscher Verlag onpact

[6] Anetis Stylianos, “The process of heat transfer and fluid flow in CFD problems”, American Journal of Science and

Technology, 2014, 1(1): 36-49

[7] “A practical formula for air-cooled boards in ventilated

enclosures”, from link: http://www.electronics-

cooling.com/1997/09/a-practical-formula-for-air-cooled-boards- in-ventilated-enclosures/

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

[9] H K Versteeg and W Malalasekara, “Computational Fluid

Dynamics- Finite Volume Method”, Text book of CFD,edition 1995

[10] Younus. A. Cengel, “Text book of Heat transfer- chapter 15- cooling of electronic equipments”


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