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Title: Numerical analysis of unsteady heat transfer for thermal management
Author: Chacko, Salvio
ISNI:       0000 0004 2735 6285
Awarding Body: University of Warwick
Current Institution: University of Warwick
Date of Award: 2012
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In this study, thermal management of Lithium ion (Li-ion) battery pack used in electric vehicle (EV) is considered. Li-ion cells generate a significant amount of heat during normal operation. Previous study has clearly identified that temperature affects the efficiency, safety, reliability and lifespan of the Li-ion battery. Therefore, a battery thermal management system (BTMS) enabling effective temperature control is essential for safety and overall performance of the Li-ion battery. Two critical aspects are key to design of efficient BTMS: firstly being able to predict the heat generated from Li-ion cells, and secondly to predict how the generated heat is removed though the cooling plate of the BTMS. To predict the heat generated from the Li-ion cell, a time-dependent, thermal behavior of a Li-ion polymer cell has been modelled for electric vehicle drive cycles with a view to developing an effective battery thermal management system. The fully coupled, new three-dimensional transient electrothermal model has proposed and implemented based on a finite volume method. To support the numerical study, a high energy density Li-ion polymer pouch cell was tested in a climatic chamber for various electric load cycles consisting of a series of charge and discharge rates, and a good agreement was found between the model predictions and the experimental data. To predict the heat removed, a numerical study has been performed on a cooling plate of a indirect liquid cooled BTMS. The BTMS has a battery cooling plate with coolant flowing through rectangular serpentine channels. The temperature distribution as well as the pressure drop across the battery cooling plate were investigated. Particular emphasis was placed on the temperature uniformity on the cooling plate surface as the lifespan of a battery is severely affected by non-uniform temperature distribution. From the simulations, it is found that the aspect ratio and the curvature have a significant effect on the surface temperature uniformity, and that a compromise of the battery cooling plate design would be required between the temperature uniformity and the pressure drop penalty. Thermal management of batteries for high discharge applications, for instance, in hybrid electric vehicle, is more challenging and typically requires turbulent heat transfer. In turbulent heat transfer not only mean temperatures but also temperature fluctuations need to be predicted correctly. For this, a numerical turbulent heat transfer of a triple jet is considered. In this study, a large eddy simulation (LES) technique was applied to predict the unsteady heat transfer behavior of turbulent flow. It is found that LES predicted the correct amplitude of temperature fluctuations which was in good agreement with the available experimental data in terms of mean, RMS, skewness and kurtosis. RANS simulations with two turbulence models were also conducted along with LES. The RANS based turbulence models produced a very small amplitude of fluctuations, and failed to predict the correct magnitude of unsteady thermal fluctuations, highlighting its limitations in unsteady turbulent heat transfer simulations. Keywords: battery thermal management; lithium-ion polymer battery; electro thermal model; EV drive cycles; finite volume method, electric vehicle; BTMS; conjugate heat transfer; battery cooling plate; rectangular serpentine channel; laminar flow; triple jet; thermal striping; mixing; thermal fatigue; LES; RANS.
Supervisor: Not available Sponsor: Warwick Manufacturing Group ; Engineering and Physical Sciences Research Council (EPSRC) ; Advantage West Midlands (AWM) ; European Regional Development Fund (ERDF)
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: TK Electrical engineering. Electronics Nuclear engineering ; TL Motor vehicles. Aeronautics. Astronautics