Western Michigan UniversitySpring 2021

Cory Burnette

Adam Clarkson

Alex Dunham

David Vidler

Design of Ventilation System for Solar Car Battery Box

Disclaimer

WESTERN MICHIGAN UNIVERSITY MAKES NO REPRESENTATION THAT THE MATERIAL PRESENTED AS A RESULT OF THIS SENIOR ENGINEERING DESIGN PROJECT IS ERROR-FREE OR COMPLETE IN ALL RESPECTS. PERSONS OR ORGANIZATIONS WHO CHOOSE TO USE THE MATERIAL DO SO AT OWN RISK.

Acknowledgements

Main Faculty Advisor

• Dr. Hosung Lee

Special Thanks

• Dr. Mitchell Kiel – Mechanical Advisor to Sunseeker

• Dr. Bradley Bazuin – Electrical Advisor to Sunseeker

• Dr. Hady Makhmalbaf – Fan selection guidance

WMU Sunseeker Solar Car

• American Solar Challenge (ASC)-main event for 2020 Solar Car

• Formula Sun Grand Prix (FSGP)

• Located in Topeka, Kansas-Maximum Expected Outside Temperature (120F)

2010 Sunseeker Car

TerminologyBattery Cell (Panasonic

NCR18650B)

Battery Module- 12

Battery Cells in parallel

“Battery Pack” 35 battery modules in

series

“BPC”

Battery PackCompartment

Design Scope

Battery Box

Contains battery pack compartment and electrical components, held in the left pontoon

Battery Pack Compartment (BPC)

Requires airflow to cool battery cells

Project Focus

Ventilation System of Battery Box

Problem

Battery cells risk overheating

Overheating can lead to battery pack catching fire

BPS shuts off the car systems if cells reach a critical temperature

60C while discharging

45C while charging

ASC regulates how the Battery Pack must be cooled

No forced ventilation at inlet to battery box

•Any fans must be located at the outlet of battery box

Objective

• Design and model a Ventilation System that sufficiently cools the Battery Pack

➢ Keep temperature of BPC under maximum allowable temperature

➢ Select an appropriate fan for the system with given power limitations

➢ Meet needs of the Sunseeker Team

• Light-weight materials

• Readily detachable from the vehicle

• Battery Box will be removed frequently for service and repairs

• ASC Regulation-compliant

Material Selection

• Intakes air flowing across inside surface of the pontoon

Naca Duct

• Easily bendable

• Easily detachable, when Battery Box must be removed

• Rougher than solid ducting; not extremely important for application

• Relatively low cost

3” Flex duct over solid ducting

• Used to spread evenly across much larger BPC area

Diffuser

Naca Duct

Flex Ducting

Diffuser

Methods

• Analytical Model (MathCAD)➢Enthalpy Model - Estimate flow rate

required➢Continuity Model - Volumetric Flow

Rates through system ➢Bernoulli’s Model - Friction Pressure

losses through system➢Convection Model - Estimate battery cell

surface temperature➢Reynolds Model - Estimate turbulent

flow

• Numerical Model (Ansys Fluent)➢ Inlet Model- Verify Pressure Loss➢Model of Full Battery Module

➢Verify models

Ventilation System Design

Sections of System

o NACA Duct Model

• Reynolds

o Inlet Duct Models

• Reynolds

• Continuity

• Bernoulli

o Diffuser Model

• Continuity

o BPC Models

• Reynolds

• Enthalpy

• Convection

• Continuity

• Bernoulli

Analytical Model Assumptions

Car Cruising Velocity is Steady

Inlet Duct Velo. = 70% Car Cruising Velo.

Density of air remains constant

Heat Dissipation from the Battery Pack is constant

Only considering Convection Heat Transfer

Enthalpy Model

• Battery Heat Generation Equation: to find max heat dissipation by the Battery Pack during Discharging

ሶ𝑄𝐿𝑜𝑎𝑑 = 𝐼2𝑅𝑖𝑛𝑡𝑒𝑟𝑛𝑎𝑙Nbatteries= 105 W

• Sensible Heat Equation: to estimate air flow rate needed to cool the Battery Packሶ

ሶ𝑉 =𝑄𝐿𝑜𝑎𝑑

𝑎𝑐𝑝𝑎∆𝑇= 16.93 cfm

➢T = Danger Temp. 140F (60C) – Max Expected Outside Temp. (120F)

➢Rough estimate, when selecting the fan, a S.F. for flow rating will be used

Analytical: Pressure Loss Model

• The Continuity equation: Used to apply constant flow rates across each section

ሶ𝑉𝐴1 = ሶ𝑉𝐴2• The Extended Bernoulli’s equation: to model pressure loss across the

System

• Used Reynold’s number models: to model turbulence, through each section of the system

Analytical: Pressure Loss Sections

• Inlet Duct

➢Treated as a pipe with surface roughness, =.007 ft (Average for Flex Duct)

➢Used K factors for a 90 and 45 turn

• Battery Pack Compartment➢Friction factor for a Staggered Tube Array for 1 Battery Module

➢Multiplied by 12 modules for the entire cross section of the Battery Pack

Analytical: Pressure Loss Results

Car Cruising Vel. (mph)

Flow Rate (CFM)

Flow Rate (m3/s)

5 15.118 0.007135

10 29.664 0.014

15 44.496 0.021

20 61.448 0.029

25 76.28 0.036

30 91.112 0.043

35 105.944 0.05

40 120.776 0.057

45 135.608 0.064

50 150.44 0.071

55 165.273 0.078

60 182.224 0.086

Analytical: Convection Model• Used the Convection Equation to

model Battery Cell Surface Temp.

• 𝑇𝑆𝑢𝑟𝑓𝑎𝑐𝑒 = 𝑇𝑜𝑢𝑡𝑠𝑖𝑑𝑒 +𝑄𝑑𝑖𝑠𝑠𝑖𝑝𝑎𝑡𝑒𝑑

𝐴𝑝𝑎𝑐𝑘ℎ𝑓

• Outside temp. was varied from 300K-320K represented by the 5 curves

• Red= Danger Temp. (60C or 333K)

Numerical Modeling: Overview

• Ansys Simulation Software• Fluent CFD Solver

• Ansys Education License• Remote access through WMU’s

CEAS Computer Lab

• 500,000 Node Limit

Mesh Example

Two Modelsd

Inlet Duct❖ Pressure Drop (friction loss)

❖ Compare to Bernoulli Model

Battery Module❖ Average Surface Temperature of Cells

❖ Convection model❖ Pressure Drop

❖ Staggered Tube Array model

Battery Pack❖ Same as battery module

Geometry

• Imported from Solidworks

• 45 elbow and 90 elbow

• 2 bodies: Pipe & Fluid Domain

Mesh

• Began with default mesh• Low resolution

• Determined “areas of interest”• Simulated default mesh,

then adjusted

Inlet

outlet

• Model• Energy Equation

• k-Omega vs k-Epsilon• Best-suited for flow near the wall

• Materials• Fluid: Air

• Solids: Aluminum (ducting)

• Boundary Conditions• Inlet velocity: Parametrized

• Based on common expected flow rates

• Solution Method• Coupled Scheme

• Calculation• Converged after 100 iterations

Output Parameters

Input Parameters

Results – Velocity Magnitude Streamline

for vinlet = 9.388𝑚

𝑠

Inlet Duct: Results Comparison of

Analytical & Numerical Models

Output Parameters

Inlet Duct Pressure Loss

VelocityAnalytical

ModelNumerical

Model

Error %Car

(mph)

Inlet (mph)

ΔP(Pa)

ΔP(Pa)

15 10.5 15.22 17.77 7.73%

20 14 27.044 29.18 3.80%

25 17.5 42.243 42.51 0.32%

30 21 60.817 58.63 1.83%

Numerical Model: Battery Module

Geometry• Fluid Doman (fluid)

• Intended to emulate air-space

between battery holders

• 12 Battery cells (solid)

Named Selections• “Inlet”

• “Outlet”

• “Battery Cells – solids”• All 12 battery cells

• This avoids complications with applying BCs

• “Symmetry Walls”• Necessary for proper inflation during meshing

Numerical Model

• Very coarse mesh• Avg global element size: 8.24mm (default)

• Areas of Interest: Boundary layer between fluid

• Improvements• Required higher resolution throughout

• Required inflation at convection boundary layer

• Just under 500,000 node limit• Average global element size: 1.5mm

• Utilized Multizone method

• Added inflation to edges • 7 layers 0.4 transition ratio

Default Mesh Final Mesh

Battery Module Mesh

Numerical Model: Battery Module Fluent Set-up + Solution

• Model

• Energy Equation

• k-Omega

• Materials

• Fluids: Air

• Solids: PVC (user-defined)

• Cell Zone Conditions

• Battery Cells

• Heat generation of 15,110 𝑊

𝑚3

• Boundary Conditions

• Inlet Velocity (Parametrized)

• Inlet Temperature (Parametrized)

• Calculation• Converged after 35 iterations Temperature contour for “DP 8”

(i.e. v = 0.708𝑚

𝑠Tinlet = 300𝐾)

Input Parameters Output Parameters

Convection Models: Analytical vs Numerical

• 𝑇𝑜𝑢𝑡𝑠𝑖𝑑𝑒 = 300𝐾

Velocity Analytical Numerical

Error %Car (mph)

Inlet(mph)

Avg Surface Temp. (K)

Avg. Surface Temp. (K)

15 0.531 300.861 302.42 0.518%

20 0.708 300.724 301.98 0.418%

25 0.885 300.634 301.67 0.345%

30 1.062 300.568 301.46 0.297%

Numerical Analysis: Battery Pack Extrapolation

• Mesh limit would not allow Battery Pack to be simulated using Fluent• Default mesh required approximately

• 3.6M elements

• 760,000 nodes

• Decided to extrapolate battery module data• 4 consecutive Battery Module simulations

(4 waves)• Used output parameters from one wave as inputs for

next wave

Wave 3

Wave 4

Wave 2

Wave 1

vin

Wave 4

Wave 2Wave 1

Extrapolating for Battery Pack: Results

Wave 3

vinlet = 0.708𝑚

𝑠(i.e. when vcar = 20mph)

Tinlet

NumericalAnalytical Error %

Wave 1 Wave 2 Wave 3 Wave 4 Pack Avg

290 292.96 297.86 300.95 301.99 298.44 291.897 2.242%

300 301.98 302.3 302.4 302.33 302.2525 301.897 0.118%

310 311.65 306.67 303.84 302.69 306.2125 311.897 1.823%

320 321.39 311.15 305.52 303.18 310.31 321.897 3.600%290

295

300

305

310

315

320

325

285 290 295 300 305 310 315 320 325

Average Tsurf

for Single Cell in Battery Pack

Temperature of Air at the Inlet [K]

Average Tsurface across Battery Pack vs Tinlet

Numerical Model

Analytical Model

Convection Models: Analytical vs Numerical

Fan Selection Logic

• Need two parameter to select an efficient fan for a system - Required Flow Rate and Pressure Loss

• Required Flow Rate for 105W dissipated➢Sensible Heat Equation gave, ሶ𝑉𝑟𝑒𝑞𝑢𝑖𝑟𝑒𝑑=16.93 CFM ➢Safety Factor = 1.76

➢Conservative estimate for Fan Selection , ሶ𝑉𝑟𝑒𝑞𝑢𝑖𝑟𝑒𝑑=30 CFM

• Pressure Loss for Fan

➢ ሶ𝑉𝑟𝑒𝑞𝑢𝑖𝑟𝑒𝑑 ሶ𝑉10𝑚𝑝ℎ so, Pressure Loss was taken at P=10.22 Pa or .04 in H2O

• Need to choose a low power fan to avoid unnecessary drain from Batteries

Fan Selection

3412 NG Fan Performance Curve

3412 NG Dimensions3412 NG

DC Axial Fan

Fan Additions• Thermal Sensor

Summary Chart

Inlet Duct Pressure Loss

Velocity Analytical NumericalError %

Car (mph) Inlet (mph) ΔP (Pa) ΔP (Pa)

15 10.5 15.22 17.77 7.73%

20 14 27.044 29.18 3.80%

25 17.5 42.243 42.51 0.32%

30 21 60.817 58.63 1.83%

BPC Pressure Loss (1 module)

Analytical Model

ANSYS Model

Car Velocity (mph)

BPC Velocity (mph)

Pressure Loss (Pa)

Pressure Loss (Pa)

Error %

15 1.187 0.646 4.012 75.60%

20 1.583 1.15 7.48 73.34%

25 1.979 1.797 10.81 71.50%

30 2.375 2.588 14.78 70.20%

Conclusion

• Two Methods Used to Validate the Selection of the 3412 NG DC Axial Exhaust Fan

➢ Ansys ➢ MathCAD