COOLING SYSTEM DEVELOPMENT

BATTERY PERFORMANCE IN ELECTRIC CARSEV batteries are quite different from those used in consumer electronic devices such as laptops and cell phones. They are required to handle high power (up to a hundred kW) and high energy capacity (up to tens of kWh) within a limited space and weight and at an affordable price. The desirable features of batteries for vehicle applications are: - High specific power - High specific energy- High charge acceptance rate for recharging and regenerative braking- Long cycle life

companyCountryVehicle modelBattery technologyGMUSAChevy-VoltSaturn Vue HybridLi-ionNiMHFordUSAEscape, Fusion, MKZ HEVEscape PHEVNiMHLi-ionToyotaJapanPrius, LexusNiMHHondaJapanCivic, InsightNiMHHyundaiSouth KoreaSonataLithium polymerChryslerUSAChrysler 200C EVLi-ionBMWGermanyX6Mini E (2012)NiMHLi-ionBYDChinaE6Li-ionDaimler BenzGermanyML450, S400Smart EV (2010)NiMHLi-ionMitsubishiJapaniMiEV (2010)Li-ionNissanJapanAltimaLeaf EV (2010)NiMHLi-ionTeslaUSARoadster (2009)Li-ionThinkNorwayThink EVLi-ion, Sodium/Metal ChlorideTable: Batteries used in electric vehicles of selected car manufacturers.

Lithium-Ion BatteryThe lithium ion battery makes use of lithium cobalt oxide (which has superior cycling properties at high voltages) as the positive electrode and a highly-crystallized specialty carbon as the negative electrode. It uses an organic solvent, as the electrolytic fluid.

Principle of OperationThe principle behind the chemical reaction in the lithium ion battery is :During cell charge,lithium in the positive electrode lithium cobalt oxide material is ionized during charge, and moves from layer to layer in the negative electrode. During discharge, Li ions move to the positive electrode and return to the original compound.

Li-ion Battery Unit Cell(Battery Chemistry LiFePO4)

Figure: Unit module of battery (2S2P)Capacity, Q=86AhSOC 10% SOC95%COOLING SYSTEM DEVELOPMENT

Why thermal management is important?

To maintain the temperature across the entire pack of batteryTo prevent rapid cell degradationTo increase battery lifeTo prevent from catastrophic destruction (fire and explosion)

Figure 1: EV battery pack cooling flowpaths with temperature distribution on cells

Figure 2: how cooling systems for electric car operates

Figure 3: IIUM Proton Green Mobility Challenge 2012 Proposed Battery Thermal Management System: Two-Phase Evaporative CoolingAdvantagesTwo-phase air-evaporative cooling system has been developed to prevent the battery spike-up temperature, keep the variation of battery temperature in the range 30-35 C and span the battery life and performance

Mechanism of two-phase evaporative coolingat evaporator ducts heat generated from the modules will be absorbed by the evaporating refrigerant (refrigerant changes state: liquid vapor)at compressor compress vapor to be high pressurize vapor, and acts to circulate the refrigerant through the whole systemat condenser unit heat carried by the refrigerant will be dissipated to surrounding via condensation process, with the aid of ventilation by a fan at expansion valve change from high pressure liquid to low pressure liquid to enter the evaporator ductThe two-phase evaporative cooling system will cool the battery pack by a direct refrigerant-based evaporative cooling. The heat generated inside battery modules will be absorbed by the refrigerant and this heat will then be dissipated to surrounding air.This application is the utilization of independent evaporator or cooling duct, condenser and compressor unit specifically for the battery cooling System, whereby the evaporator or cooling duct will be connected in parallel to the main refrigerant circuit. The refrigerant will be circulated in a closed-loop, where a suction line will withdraw refrigerant from cooling ducts (evaporator), rise the pressure to a higher level and discharge it to a condenser to dissipate heat to the surrounding before it reaches the expansion valve to reduce pressure for flashing and evaporation of liquid in the cooling ducts absorbing heat from surface (battery modules surface) to be cooled.