Battery Thermal Management 

Design Modeling

Gi-Heon Kim, Ph.DAhmad Pesaran, Ph.D (ahmad_pesaran@nrel.gov

National Renewable Energy Laboratory, Golden, C

E

NREL/PR-540-40848

With support fromHigh Power Energy Storage Program (Tien Duong and Dave H

Office of FreedomCAR and Vehicle TechnologiesEnergy Efficiency and Renewable Energy OfficeU.S. Department of Energy 
Motivations & ObjectivesMotivations

 Battery thermal management is critical in achieving p

extended life of batteries in electric and hybrid vehic

 Appropriate models that can predict thermal behavio

shorten the development process for improving batte

Objectives of this Study

 To investigate the impact of cooling strategies with d

systems; air and direct/indirect liquid cooling 

 To evaluate system thermal responses and their sen

function of controllable system parameters

 To provide battery thermal management system des

identifying analyses and approaches that engineers when they design a battery thermal management sy

and hybrid vehicles 
Battery Thermal Responses

3D

Component

Analysis

System

Analysis

Cell Characteristics

• Shape: Prismatic/Cylinder/Oval etc

• Materials/Chemistries• Size/Dimensions/Capacity• Thermal/Current Paths inside a Cell Module Cooling Strategy

• Passive control with phase change 

• Coolant type: Air/Liquid• Direct Contact/Jacket Cooling• Serial/Parallel Cooling• Terminal/Side Cooling• Module Shape/Dimensions• Coolant Path inside a Module• Coolant Flow Rate• etc

Battery Th

Battery Th

Mod

Mod

• Temperature History Cells/Module/Pack• Temperature Distribution in a Cell • Cell-to-Cell Temperature Imbalance in a Mod

• Battery Performance Prediction• Pressure Prop and Parasitic Power

• etc.

Design Process
Approach

 NREL has developed a 3-D electro-thermal m

thermal response of real cells – focus on cell temperature (EVS-21)

 In this study, focus is mostly external to cell – 

– Air cooling– Liquid cooling

• Direct• Indirect

 The battery management system response w

using

– Fully developed laminar channel flow analysis– Computational Fluid Dynamic (CFD) analysis

 The system responses oof interest were 

– Coolant temperature change (outlet - inlet) – Temperature difference between cell surface and bulk – Pressure drop in coolant channel (fluid power requirem
Typical Parallel Cooling Analys(all the cells are treated the same)

cell surface temperaturecoolant mean temperaturepressure

Heat Transf

Properties

 Density Specific He Thermal C ViscosityCell Specifi Dimension Heat GeneControl Par Coolant M

 Coolant Ch

ΔT2ΔT1

ΔP : Channel P

: Coolant Te: Coolant-C

System Respons

P

x

T

x

ΔT2

ΔT1

ΔP

Dcell

Lcell

Q

0.5Dh

mc

. . Dcell

Lcell

Q

0.5Dh

mc

. .
Fully Developed Laminar Flow AnaAnnular Channel Cooling

= 24Re

f

c

= 5.385Nu

ν

VD

h where, , Re

=

If coolant channel gap is small enough compared with cell diameter,

k

hD

h Nu

=

Ce

ν (m2/s) 1

k (W/m K) 

cp (J/kg K) 

? (kg/m3) 

ν (m2/s) 1

k (W/m K) 

cp (J/kg K) 

? (kg/m3) 

Heat 

ΔP = 

4

τ

ΔT2 = Q/(πDcellLh)

oL/D

h

ΔT1 = Q/( cp

m& )

hydraulic diameterDh = 4 Ac / p 

whereAc : area section of the channel 

p :perimeter of the channel

mean velocityV = / (ρAc) 

whereρ : coolant density 

: coolant mass flow rate

m&

m&

Con

m&

D

h

System Responses

ρ

: Co: HyCha
Channel Pressure Loss 

ΔP

 Large difference in kinematic viscosity 

Æ, ΔP varies in very differe



ΔP inversely proportional to 

D

h

3 at 

Dcell >> 

D

h and laminar flow

 The channel pressure loss changes are very sensitive to 

D

h when 

 Due to the much smaller fluid density and consequently larger vol

given mass flow rate, the air cooling system requires much higher 

1 2 3 4 5 6 7 8

10-1100101102103104

Dh (mm)

AirMineral OilWater/Glycol

1 2 3 

10-1100101102103104105106

Power/mc

2 [W/(kgs-1)2] . Power/mc2 [W/(kgs-1)2] .

ΔP/mc [kPa/(kgs-1)] . ΔP/mc [kPa/(kgs-1)] .

(a) (b)

Δ

Mass-rate specific pressure Square-of-mass-r
Coolant Temperature Increase 

0.5 1 1.5

2 2.5

3 3.5

4

0

0.5

1

1.5

2

2.5

3

3.5

4

Mass-Flow Rate (g/s)

Temperature (oC)

p

AirMineral OilWater/Glycol

ΔT1

pc cm

Δ

T &

1 1 ~

2

1 11

~

p

m

c

cm

Δ

T

& & −

∂

∂

 To achieve th

over a cell, it coolant tempchannel as s



ΔT1 is inverse

heat capacity 

 Therefore, in

not as effectitemperature cooling as it cooling. 

 A little chang

affect the cooand consequsmall coolant air system ha
Temperature Difference between Coolant Bulk and Cell Su

1 2 3 

0

100200300400500600700800900

1000

h (W/m2K)

Heat 

1 2 3 4 5 6 7 8 0

12345678

Dh (mm)

Temperature (oC)

Temperature Difference Between Coolant & Cell Surface

AirMineral OilWater/Glycol

h



ΔT2 varies linearly with 

D

h with slope being proportional to 1/

k .



ΔT2 rapidly increases with 

D

h in air cooling due to its small therm

 The heat transfer coefficient (

h) evaluated at cell surface for wate

greatly reduced and not sensitive to channel height due to added between coolant and cell surface.

 High 

h system reduces 

ΔT2, and removes heat fast from small te

ΔT2
1.6 1.8 2

2 2.2

2.2

2.4

2.4 2.6

2.6

2.8

2.8

3

3

3

3.2

3.2

3.2

3.4

3.4

3.4

3.6

3.6

3.6

3.8

3.8

3.8

4

4

4

4.2

4.2

4.2

4.4

4.4

4.4

4.6

4.6

4.6

4.8

4.8

4.8

5

5

5

5

5.2

5.2

5.2

5.4

5.4

5.4

5.6

5.6

5.6

5.8

5.8

5.8

6

6

6

6

6.2

6.2

6.2

6.4

6.4

6.4

6.6

6.6

6.6

6.8

6.8

6.8

7

7

7

7

7.2

7.2

7.2

7.4

7.4

7.4

7.6

7.6

7.6

7.8

7.8

7.8

8

8

8

8

8.2

8.2

8.2

8.4

8.4

8.4

8.6

8.6

8.8

8.8

9

9

9.2

9.2

9.4

9.69.8 1100.210.4 10.610.8 11

Dh(mm)

mass flow rate (g/s)

DT

max (oC)

1 2 3 4 5 6 7 8

0.5

1

1.5

2

2.5

3

3.5

4

0.6

0.8

0.8

1

1

1

1.2

1.2

1.2

1.4

1.4

1.4

1.4

1.6

1.6

1.6

1.6

1.8 1.8

1.8

1.8

2 2

2

2.2 2.2 2.2

2.4 2.4 2.4 2.6 2.6 2.8 2.8 3 3 3.2 3.4

Dh(mm)

DT

max (oC)

1 2 3 4 5 6 7 8

0.5

1

1.5

2

2.5

3

3.5

4

1

1.6 

1.8 

2 

1 

0.5

1

1.5

2

2.5

3

3.5

4

1.6 1.8 2

2 2.2

2.2

2.4

2.4 2.6

2.6

2.8

2.8

3

3

3

3.2

3.2

3.2

3.4

3.4

3.4

3.6

3.6

3.6

3.8

3.8

3.8

4

4

4

4.2

4.2

4.2

4.4

4.4

4.4

4.6

4.6

4.6

4.8

4.8

4.8

5

5

5

5

5.2

5.2

5.2

5.4

5.4

5.4

5.6

5.6

5.6

5.8

5.8

5.8

6

6

6

6

6.2

6.2

6.2

6.4

6.4

6.4

6.6

6.6

6.6

6.8

6.8

6.8

7

7

7

7

7.2

7.2

7.2

7.4

7.4

7.4

7.6

7.6

7.6

7.8

7.8

7.8

8

8

8

8

8.2

8.2

8.2

8.4

8.4

8.4

8.6

8.6

8.8

8.8

9

9

9.2

9.2

9.4

9.69.8 1100.210.4 10.610.8 11

Dh(mm)

mass flow rate (g/s)

DT

max (oC)

1 2 3 4 5 6 7 8

0.5

1

1.5

2

2.5

3

3.5

4

0.6

0.8

0.8

1

1

1

1.2

1.2

1.2

1.4

1.4

1.4

1.4

1.6

1.6

1.6

1.6

1.8 1.8

1.8

1.8

2 2

2

2.2 2.2 2.2

2.4 2.4 2.4 2.6 2.6 2.8 2.8 3 3 3.2 3.4

Dh(mm)

DT

max (oC)

1 2 3 4 5 6 7 8

0.5

1

1.5

2

2.5

3

3.5

4

1

1.6 

1.8 

2 

1 

0.5

1

1.5

2

2.5

3

3.5

4

Air

mass flow rate (g/s)

Dh (mm) Mineral Oil

D Wate

h (mm)

Maximum Cell Surface Temperaturerelative to Coolant Inlet

ΔTmax



ΔTmax in the air system are much higher compare

systems due to its small heat capacity and therma

 The air system: 

ΔTmax is dominated by and sensiti

 The water/glycol jacket cooling system: 

ΔTmax is n

D

h, and 

ΔTmax is not a strict limiting thermal design 

water/glycol system. 
Optimizing Operation Paramet

: maximum heat transfer coefficient (h) operatin: lowest max temperature (ΔT1+ 

ΔT2 ) operating 

: minimum pressure loss (ΔP) operating point

Re=2300

Δ P=37 Pa

Δ P=110 Pa

Δ

T1

=1.5 

o

C

Δ

Tmax=4.5 

o

C

Δ

Tmax

=3.43 

o

C

- Air C
0.000.100.200.300.400.500.600.700.800.90

0 0.005 0.01 0.015 0.02 0.025 0.03 0.035 0.04 0.045

Mass Flow Rate (kg/s)

Coolant Temperature Rise (oC) Coolant Temperature Rise (o

C)

Mass Flow Rate (kg/s)

Trend Validation: Module Liquid CoExperiment

0 0.5 1 1.5 2 2.5 3 3.5 4 0

0.10.20.30.40.50.60.70.80.9

M ass-Flow Rate (g/s)

Temperature (oC)

Coolant Tem perature Inc rease

Tested M 12 li-ion  Indirect j Coolant 

fully dev

 Discharg Coolant 

increase to the co

 Coolant 

high masensitive at low m

 Note tha

coolant tgiven herelatively capacity 

prediction

experiment
Computational Fluid Dynamic (CFD) 

Cell Core

Coolant Channel

Terminal

Can

Terminal Current Collector

Geometry & Mesh Temperature 

NOTE: Radial d

Direct Air Cooling

9 Heat Generation: 2 W 9 Channel Inlet Air Tem

9 Air Mass Flow Rate: 19 Channel Gap Height: 
CFD Predictions: Temperatures, h and Surface Heat Flux 

0 1 2 3 4 5 6 7 8 9 10

35

35.5

36

36.5

37

37.5

38

38.5

39

Axial Distance (cm)

Temperature (oC)

Air Mean TemperatureCell Surface TemperatureCell Temperature at Axis

0 1 2 3 4 5 6 7 8 9 10

0

50

100150200250

Axial Distance (cm)

Heat Flux (W/m

2

)

0 1 2 3 4 5 6 7 8 9 10

0

20406080

100120

A i l Di ( )

Heat Transfer Coefficient (W/m2K)

ΔT1

ΔTmax

CFD 114.2 1.50 2.89 3.41 60.96

109.1 1.49 3.64 N/A 59.24 Fully Developed Flow Relations with Constant Heat Flux

h [W/m2K]

mean heat transfer coefficient 

ΔTcell [oC]

maximum cell internal temperature to inlet air

ΔTmax [oC]

maximum cell surface temperature to inlet air

ΔT1 [oC]

coolant temperature change

ΔP [Pa]

channel pressure loss

CFD 114.2 1.50 2.89 3.41 60.96

109.1 1.49 3.64 N/A 59.24 Fully Developed Flow Relations with Constant Heat Flux

h [W/m2K]

mean heat transfer coefficient 

ΔTcell [oC]

maximum cell internal temperature to inlet air

ΔTmax [oC]

maximum cell surface temperature to inlet air

ΔT1 [oC]

coolant temperature change

ΔP [Pa]

channel pressure loss

Heat Flux

h ΔTmax D

 CFD  CFD 

internaxiallcell to 

 Intern

condinside can) cell sthan 

 This 

captupaths inside improcell/b
Air vs Water/Glycol CFD

Dh= 2.2 mm

mc= 1.33 g/s

&

Dh= 2.2 mm

mc= 1.33 g/s

&

air wa

Lcell = 2

Dcell = 

aluminum can

jacket

cell core cell core

aluminum can

air

water/glycol

Performance comparison analyses were made between Air Cooling System and 

Water/Glycol Jacket Cooling System in order to contrast the characteristics of each system.

9 Heat G9 Channe

9 Coolan

9 Channe9 5 cm di
Concluding Remarks

 The heat transfer coefficient (

h) of an air cooling system 

liquid cooling systems. 

 Due to the small heat capacity of air, it is difficult to acc

uniformity inside a cell or between the cells in a module

 The temperature difference between coolant air and ce

to variations of channel height due to the small heat con

 Heat transfer coefficient is inversely proportional to 

D

h, 

loss in channel is inversely proportional to 

D

h

3

. 

 Increasing heat transfer coefficient by reducing channe

by the required blower power. 

 The simplicity of an air cooling system is an advantage 

system.

 Air cooling could have less mass, has no potential for le

components, and could cost less.

Air Cooling System
Concluding Remarks

 A water/glycol solution for a jacket cooling has much low

dielectric mineral oil for direct cooling. Increasing the cowater/glycol system is not as severely restricted by the mineral oil system. 

 Cell/module temperature uniformity can be effectively a

cooling system due to the large heat capacity of liquid c

 Water/glycol solutions generally have a higher thermal 

However, the effective heat transfer coefficient at the cereduced due to the added jacket wall and air gap layer.

 Because of the added thermal resistances, 

h is not as s

variation of channel height in indirect liquid cooling syst

 Liquid cooling systems are more effective in heat transf

volume.

 However, the added complexity and cost may outweigh  Maintenance and repair of a liquid cooled pack is more 

Indirect liquid cooling, with jackets, is easer to handle thcooling.

Liquid Cooling System
Concluding Remarks

 Selection between air or liquid cooling depends on 

 Trade-off between performance, application, and 

considered

 It is recommended in liquid cooling system to use 

channel to reduce system weight and volume by mamount of liquid coolant in a system operated at a rate. 

 Capturing the internal heat flow paths and therma

a cell using a sophisticated three-dimensional cell for the improved prediction of cell/battery thermal 

 With the model we can look at turbulent flows, mix

conduction/convection, and phase change materia

General