Approach for designing thermal management systems for EV and by dbn14335

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									 An Approach for Designing Thermal
 An Approach for Designing Thermal
Management Systems for EV and HEV
Management Systems for EV and HEV
          Battery Packs
           Battery Packs
  4th Vehicle Thermal Management Systems Conference
                      London, UK
                   May 24-27, 1999




                 Ahmad A. Pesaran, Ph.D.
                      Steven D. Burch
                      Matthew Keyser
           National Renewable Energy Laboratory
   CENTER FOR TRANSPORTATION TECHNOLOGIES AND SYSTEMS
Working with Industry
Working with Industry
This work was sponsored by the U.S. Department of Energy
as part of the cost-shared Hybrid Vehicle Propulsion Systems
Program.




              DAIMLERCHRYSLER
       CENTER FOR TRANSPORTATION TECHNOLOGIES AND SYSTEMS
Presentation Outline

ä Background
ä Why battery thermal management system (BTMS)?
ä Design approach for BTMS
ä Results and discussion for a battery type
ä Concluding remarks




     CENTER FOR TRANSPORTATION TECHNOLOGIES AND SYSTEMS
National Renewable Energy Laboratory



ä   NREL is one of the eleven U.S.
    Department of Energy’s national
    laboratories
ä   NREL’s mission is to develop and
    promote renewable energy and energy
    efficient technologies in various sectors
ä   NREL’s transportation activities are
    focused on alternative fuels, emissions,
    and HEV components and systems

         CENTER FOR TRANSPORTATION TECHNOLOGIES AND SYSTEMS
Electric/Hybrid Vehicles for 21st Century Transportation
  ä   Reduced emissions and pollution
                                                      Toyota Prius
  ä   Improved fuel economy
   Ford P2000 HEV




                     Audi Duo HEV

   GM Series HEV




                                                      Peugeot EV
          CENTER FOR TRANSPORTATION TECHNOLOGIES AND SYSTEMS
Battery Temperature is Important
ä Temperature     affects battery
   ä Operation  of the cells/modules
   ä Round trip efficiency and charge acceptance
   ä Power and energy
   ä Safety and reliability
   ä Life and life cycle cost


 Battery temperature affects
 vehicle performance,
 reliability, safety, and life
 cycle cost

       CENTER FOR TRANSPORTATION TECHNOLOGIES AND SYSTEMS
Thermal Management is Needed
ä   Regulate pack so it operates in the desired
    temperature range for optimum performance/life




ä Reduce uneven temperature distribution in a pack
  to avoid unbalanced modules/pack to avoid
  reduced performance
ä Eliminate potential hazard related to uncontrolled
  temperature
        CENTER FOR TRANSPORTATION TECHNOLOGIES AND SYSTEMS
Functions of Thermal Management
ä   Maintain battery pack temperature
    (heating/cooling) using
    ä air
    ä liquid (direct and indirect)
    ä insulation
    ä phase change material
    ä passive (ambient) or active (HX, heaters, A/C)
    ä combination of various approaches

ä Provide ventilation for batteries that generate
  potentially hazardous gases
ä Provide a control strategy for safe operation


        CENTER FOR TRANSPORTATION TECHNOLOGIES AND SYSTEMS
Design of Thermal Management System
ä   NREL has been working with automobile and
    battery manufactures in evaluating and designing
    battery thermal management systems (BTMS)
    ä Energy/thermal analysis
    ä Thermal characterization
    ä Fluid/heat transfer experiments
    ä Battery testing




ä   We believe a systematic approach to design and
    evaluate battery modules and packs leads to better
    battery thermal management

         CENTER FOR TRANSPORTATION TECHNOLOGIES AND SYSTEMS
A Systematic Approach for Designing BTMS
 Major Steps:
 1. Define BTMS design objectives and constraints
 2. Obtain module heat generation and heat capacity
 3. Perform a first order BTMS evaluation
 4. Predict battery module and pack behavior
 5. Design a preliminary BTMS
 6. Build and test the BTMS
 7. Refine and optimize BTMS



       CENTER FOR TRANSPORTATION TECHNOLOGIES AND SYSTEMS
Define BTMS Design Objectives and Constraints
 ä   Battery pack specifications
     ä module type
     ä number of modules
     ä geometry
     ä dimensions
     ä preliminary lay out in vehicle

 ä   Desired battery thermal performance
     ä average operating temperature
     ä acceptable module delta T
     ä acceptable pack delta T
     ä Safety constraints (e.g., need for ventilation)


         CENTER FOR TRANSPORTATION TECHNOLOGIES AND SYSTEMS
Battery Pack Specifications
ä   Depends on the type of battery
    ä Lead acid:        30 Wh/kg; 450 W/kg
    ä NiMH:             60 Wh/kg; 200 W/kg
    ä Li-Ion:           80 Wh/kg; 300 W/kg
ä   Depends on the type of vehicle
    ä EV (80 kW, 28 modules)
    ä Parallel HEV
        ä Large engine (57 kW engine; 29 kW motor, 10 modules)
        ä Small engine (30 kW engine; 46 kW motor, 16 modules)

    ä Series HEV
        ä Large engine (52 kW engine; 61 kW motor, 21 modules)
        ä Small engine (33 kW engine; 70 kW motor, 24 modules)


        CENTER FOR TRANSPORTATION TECHNOLOGIES AND SYSTEMS
Desired Thermal Performance
ä   Operating temperature depends on battery type
    ä Lead acid: 0°C to 55°C      (45°C)
    ä NiMH: -10°C to 40°C         (25°C)
    ä Li-Ion: -20°C to 60°C       (30°C)
ä   Acceptable temperature variation in module
    ä Size dependent and type dependent
       ä 2-3°C in small modules
       ä 6-7°C in large modules

ä   Acceptable temperature variation in pack
    ä Size and EV/HEV-type dependent
       ä 2-3°C in small packs (parallel HEV)
       ä 7-8°C in large packs (EV, series HEV)


        CENTER FOR TRANSPORTATION TECHNOLOGIES AND SYSTEMS
Module Heat Generation
ä   Heat generated from a module depends on:
    ä type of battery and its efficiency
    ä Conditions (temperatures; state of charge)
    ä Charge/discharge profile

ä   Heat generated could be:
    ä Measured in a calorimeter
    ä Estimated from electric energy balance
                                                    NREL Calorimeter

       Data for a 12 V HEV module       Module Heat Generation (W)
                 Cycle                    25° C          40° C
    16.5 A discharge, 80% to 20% SOC       7.7                 2.1
    16.5 A charge, 20% to 80% SOC          16.0               15.8
    HEV 1.3 FUDS, initial SOC of 75%       46.0               36.8
         CENTER FOR TRANSPORTATION TECHNOLOGIES AND SYSTEMS
Module Heat Capacity
ä   Module heat capacity depends on:
    ä Battery type
    ä Battery case
    ä Conditions (T, SOC)

ä   Heat capacity could be:
    ä Estimated based on mass-weighted average of
      components
    ä Measured in a calorimeter                      Calorimeter
                                                       cavity


           Optima 12V HEV Module
            Specific heat = 640 J/kg/K
            Density = 4035 kg/m3
         CENTER FOR TRANSPORTATION TECHNOLOGIES AND SYSTEMS
Perform a First Order BTMS Evaluation
 ä   Perform energy and thermal analysis
     ä   steady state [qb = mrf Cf (Tfo - Tfi)]
     ä   transient [mbCbdTb/dt = qb = h A (Tb - Tf)]
     ä different heat transfer medium (air, liquid, PCM)
     ä different flow paths (direct/indirect, series/parallel)
     ä different flow rates and conditions

 ä Estimate of fan/pump parasitic power
 ä Preliminary selection of the heat transfer
   medium and associated flow rate
     Is there a need for BTMS? What size and type?

          CENTER FOR TRANSPORTATION TECHNOLOGIES AND SYSTEMS
Design a Preliminary BTMS
ä   Conduct analyses and experiments to design
    ä  integrated pack thermal system
    ä size auxiliary components (fan/pump, HX, heater,
      coil)
ä Devise control strategy for operating BTMS
ä Estimate cost
ä Evaluate other factors (maintenance, ease of
  operation, reliability)
ä Compare alternative BTMS and decide on one
  option

        CENTER FOR TRANSPORTATION TECHNOLOGIES AND SYSTEMS
Build and Test the BTMS
ä Build a battery pack with an integrated BTMS
ä Conduct bench-top experiments to validate
  analysis
ä Evaluate thermal control strategies
ä Install a prototype pack/BTMS in a vehicle
ä Evaluate using a vehicle dynamometer




      CENTER FOR TRANSPORTATION TECHNOLOGIES AND SYSTEMS
Refine and Optimize the BTMS
ä Refine the analysis and design of the
  components and systems
ä Repeat previous steps considering:
    ä battery performance and life
    ä impact on vehicle performance
    ä cost
    ä maintenance
    ä reliability

ä   Finalize the optimum design


        CENTER FOR TRANSPORTATION TECHNOLOGIES AND SYSTEMS
2-D Pack Thermal Analysis
  30 Modules
  For a EV or Series HEV




             Heat Generation: 35 W/module

     CENTER FOR TRANSPORTATION TECHNOLOGIES AND SYSTEMS
Pack FEA thermal analysis predicts
behavior of various designs
                                           Closed, no flow
                                           Tmax = 144ºC
                                           Tmin =40ºC
                         Air entering at 25ºC            Air leaving at 38ºC

Open, series air flow
air flow: side to side
  Tmax = 58ºC
  Tmin =40ºC
                                   Air leaving at 38ºC

     Open, parallel air flow
     air flow: bottom to top
        Tmax = 54ºC
        Tmin = 46ºC
                                  Air entering at 25ºC
         CENTER FOR TRANSPORTATION TECHNOLOGIES AND SYSTEMS
Analysis Indicated Thermal Improvement
by Adding Cooling Holes
                            No Holes
      Cell core         Tmax = 53ºC
Air           Plastic   Delta Tcore = 13ºC
gap           case




                           With Holes
                          Tmax = 44ºC
                          Delta Tcore = 9ºC
           CENTER FOR TRANSPORTATION TECHNOLOGIES AND SYSTEMS
3-D Module Thermal Analysis
ä   Based on a prototype HEV module by Optima Batteries
    (Aurora, Colorado, USA)




                                          Spirally-wound cylindrical cells




 Valve regulated, lead acid



                              6-cell modules (12 V, 16.5 Ahr, 2.9 kW, 6 kg)
          CENTER FOR TRANSPORTATION TECHNOLOGIES AND SYSTEMS
Estimating Thermal Conductivity of Optima Cells
                          Qx = kx ∆ T / ∆ x
                                                    A section of cell
                                                    with two lead grid


                                                    A section of cell with
                                                    all cell elements


                                Apply known ∆ T across two x planes
                                Find Qx and calculate overall kx


  Axial:        Ave: keff,a = 9.5 W/mK
  Radial        Ave: keff,r = 6.6 W/mK
  Tangential:   Ave: keff,t = 8.8 W/mK

         CENTER FOR TRANSPORTATION TECHNOLOGIES AND SYSTEMS
3-D Thermal Evaluation of Optima Module
                                                                               CAD Finite element
                                                                               thermal analysis



                                                                                                                           30
                                                                                                                           31
                                                                                                                           32
                                14                                                                                         33
                                                                                                                           34
                                                                                                                           35
                                12                                                                                         36
Cell Heat Generation Rate [W]




                                                                                                                           37
                                                                                                                           38
                                10
                                                                                                                           39
                                                                                                                           40
                                                                                                                           41
                                 8



                                 6



                                 4
                                                                                      Non uniform heat generation
                                                                                      due to non uniform current density
                                 2
                                  0.0   0.2          0.4          0.6           0.8    1.0
                                         Normalized Axial (Vertical) Cell Location

                                        CENTER FOR TRANSPORTATION TECHNOLOGIES AND SYSTEMS
                                       Comparison of Air versus Liquid Cooling
                              55
                                                                                                                                         Based on the same
                                                                                           o
                                                                                Ttop,SS = 54 C

                              50
                                            Air cooled
                                       Air Cooled
                                                                                                                                          parasitic power
                                       h = 18 W/Km2
                                       Q = 5 W/cell
Max. Cell Temperature [ oC]




                                                o
                                       Tt=0 = 30 C                                                                             Top
                                       Tair = 25 o C
                                                     2
                              45       hair = 18 W/m K                                                                         Middle

                                                                                                                               Bottom


                              40
                                                                                                                                55

                                                                                                                                         Oil Cooled
                              35                                                                                                         Q = 5 W/cell
                                                                                                                                50                Liquid cooled
                                                                                                                                                  o
                                                                                                                                         Tt=0 = 30 C
                                                                                                                                                      o




                                                                                                 Max. Cell Temperature [ oC]
                                                                                                                                          Toil = 25 C
                                                                                                                                                 =h W/m 28 W/Km2
                                                                                                                                                  28 = K
                                                                                                                                                          2
                                                                                                                                          hoil
                              30                                                                                                                                                                o
                                                                                                                                                                                     Ttop,SS = 45 C
                                   0        10           20       30       40         50                         60
                                                                                                                                45
                                                              Time [min]
                                                                                                                                                                                                           Top


                                                                                                                                40                                                                         Middle

                                                                                                                                                                                                           Bottom


                                                                                                                                35
                                                 Liquid cooling
                                                 more effective                                                                 30
                                                                                                                                     0           10           20       30       40        50          60

                                                                                                                                                                   Time [min]

                                                              CENTER FOR TRANSPORTATION TECHNOLOGIES AND SYSTEMS
Infrared Thermal Imaging as a Diagnostic Tool
 Image of Optima module during and HEV FUDS cycle




        CENTER FOR TRANSPORTATION TECHNOLOGIES AND SYSTEMS
Evaluation of Two Optima Battery Packs
for a Parallel HEV
® Each pack consists of 12 Optima HEV modules in a 3X4 layout

                                             Parallel flow:
                                              modules upright
                                              airflow up




Series flow:
 modules on side
 airflow across




        CENTER FOR TRANSPORTATION TECHNOLOGIES AND SYSTEMS
      Transient and Steady-State Thermal
      Analysis of the First Module in two Packs
                        Higher flow rate and h results in lower temperature in series flow pack.

                                          55
Max. Cell Temperature in Module #1 [ C]




                                                                                                               o
o




                                                                                              Steady-State: 51 C
                                          50


                                                           PARALLEL FLOW
                                          45                 Cells upright
                                                              Airflow up

                                          40
                                                                                               Steady-State: 38 oC


                                          35
                                                                        SERIES FLOW
                                                                         Cells on side
                                                                        Airflow across
                                          30
                                                                                     pack is 57 L/s
                                                   Total airflow rate through each Initial cell temp.: 30 oC
                                                   Inlet air T = 25°C                Airflow: T = at 25 o
                                                                            Initial Module 57 L/s 30°CC
                                          25
                                               0      10         20          30          40          50              60

                                                                      Time [minutes]

                                                   CENTER FOR TRANSPORTATION TECHNOLOGIES AND SYSTEMS
                                         Steady-State Temperature Distribution in
                                         all Modules in the two Packs
More uniform module temperature in parallel flow pack because of even flow distribution.
                                         55
                                                                                                 PARALLEL FLOW
                                                                                                   Cells upright
                                                                                                    Airflow up
    Steady-State Cell Temperature [ C]




                                         50
   o




                                         45



                                         40



                                         35
                                                                                                   SERIES FLOW
                                                                                                    Cells on side
                                                                                                   Airflow across
                                         30
                                                  Cooling airflow: 57 L/s
                                                   Total airflow rate through each pack is 57 L/s
                                                                     o
                                                         Total 25 C
                                                  Inlet air temp:airflow rate through each pack is 57 L/s
                                                   Inlet air T = 25°C        Initial Module T = 30°C
                                         25
                                              0        2           4          6           8          10             12

                                                                        Module Number

                                                     CENTER FOR TRANSPORTATION TECHNOLOGIES AND SYSTEMS
Experimental Pressure Drop and associated
Fan Power for the two Packs
                                                  Blower-motor efficiency = 25%
                             500                                                          300
                                              Parallel Flow -DP
Pressure Drop Across Pack (Pa)



                                              Series Flow - DP                            250
                             400              Parallel Flow -Power
                                              Series Flow -Power
                                                                                          200




                                                                                                Fan Power (W)
                             300

                                                                                          150

                             200
                                                                                          100

                             100
                                                                                          50


                                 0                                                        0
                                     0       20       40        60        80      100   120
                                                        Air Flow Rate (L/s)

                                         CENTER FOR TRANSPORTATION TECHNOLOGIES AND SYSTEMS
Concluding Remarks
ä   A well-designed thermal management system can
    improve performance and life cycle of EV/HEV battery
    packs.
ä   A step-by-step approach for designing and evaluating
    thermal management system was outlined.
    ä   Define requirements
    ä   Characterize thermal properties
    ä   Perform analysis - preliminary & detailed
    ä   Build, test, refine




          CENTER FOR TRANSPORTATION TECHNOLOGIES AND SYSTEMS
Concluding Remarks
ä   Air thermal management system is less complicated
    than a liquid system, but less effective.
ä   For parallel HEVs, an air thermal management system
    is adequate, where as for EVs and series HEVs, liquid
    based systems may be required.
ä   For further information visit our Battery Thermal
    Management Web Site www.ctts.nrel.gov/BTM.




         CENTER FOR TRANSPORTATION TECHNOLOGIES AND SYSTEMS

								
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