Design of Ventilation System for Solar Car Battery Box
Transcript of Design of Ventilation System for Solar Car Battery Box
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