Session: K6-04: HEAT TRANSFER IN ENERGY SYSTEMS - ENERGY STORAGE II

Paper Number: 137288

137288 - Numerical Comparison of Heat Rejection Techniques for Electric Vehicle Battery Thermal Management Systems 

Abstract: 

Electric vehicles (EVs) are increasing in market share due to a global effort to reduce greenhouse gas emissions. Battery thermal management systems (BTMS) play an important role in battery performance by regulating the temperature of the EV battery pack. Operating temperature has an impact on the lifetime and health of lithium-ion batteries, thus a BTMS is essential to maximizing the lifetime of the batteries and reducing EV maintenance costs. Prior BTMS research primarily focuses on the interface between the battery and the cooling system. Both computational and experimental work have investigated this interface by analyzing parameters such as flowrate, flow configuration, channel width, cell spacing, etc. However, a system-level analysis that includes analyzing how heat from the cells is rejected to the ambient environment is needed because it significantly impacts the effectiveness of BTMS. As such, the objective of the current research is to analyze rejecting heat via two common approaches: a radiator and a vapor compression cycle (VCC).  To conduct this research objective, a transient, multi-domain, system-level model of a BTMS is used. The battery heat generation rate is calculated using a lumped-parameter model. The radiator is modeled as a cross-flow heat exchanger where the battery coolant rejects heat to the ambient air. The VCC model consists of an evaporator, compressor, condenser, and throttling valve. Within the evaporator, heat transfer occurs between the battery coolant and the VCC refrigerant. For the battery-cooling-system interface, direct liquid cooling, indirect liquid cooling, and air-cooling methods are modeled. System designs that contain one heat rejection method and the two in combination are modeled. Low-stress (low ambient temperature, low discharge rate) and high-stress (high ambient temperature, high discharge rate) conditions are modeled and compared. A finite difference approach is used to solve the governing equations.  Operational constraints such as maximum battery temperature, parasitic power consumption, and added mass and volume are considered. Results show that the choice of battery-cooling system interface significantly impacts the required sizing of the heat rejection components.  Given low-stress conditions, the radiator can maintain desirable battery temperatures with low parasitic power consumption. However, the heat transfer in the radiator can easily become the limiting factor in the performance of the BTMS. The use of the VCC reduces this pinch point and allows for the battery coolant to be cooled below ambient temperature, which results in cooler battery temperatures. However, the added benefit that the VCC provides bears the cost of significantly increased parasitic power consumption, e.g. order of magnitude greater, due to the compressor. A BTMS with a VCC should be operated in such a way as to minimize its use. As such, the results highlight the importance of considering the design and effect of the heat rejection method when developing the BTMS. 

DISTRIBUTION A. Approved for public release; distribution unlimited. OPSEC #8229

 

Presenting Author: Samuel Tillma North Dakota State University

Presenting Author Biography: Samuel Tillma is a Graduate Research Assistant at North Dakota State University working under the guidance of Dr. Adam C. Gladen on battery thermal management systems.

Authors:

Samuel Tillma North Dakota State University
Adam C. Gladen North Dakota State University