Date of Award

May 2021

Document Type


Degree Name

Doctor of Philosophy (PhD)


Mechanical Engineering

Committee Member

Richard Miller

Committee Member

Denise Rizzo

Committee Member

Xiangchun Xuan


Emphasis on reducing fossil fuel consumption and greenhouse gas emissions, besides the demand for autonomy in vehicles, made governments and automotive industries move towards electrification. The integration of an electric motor with battery packs and on-board electronics has created new thermal challenges due to the heat loads' operating conditions, design configurations, and heat generation rates. This paradigm shift necessitates an innovative thermal management system that can accommodate low, moderate, and high heat dissipations with minimal electrical or mechanical power requirements.

This dissertation proposes an advanced hybrid cooling system featuring passive and active cooling solutions in a thermal bus configuration. The main purpose is to maintain the heat loads’ operating temperatures with zero to minimum power requirements and improved packaging, durability, and reliability. In many operating instances, a passive approach may be adequate to remove heat from the thermal source (e.g., electric motor) while a heavy load would demand both the passive and active cooling systems operate together for reduced electric power consumption. Further, in the event of a failure (e.g., coolant hose leak, radiator tube leak) in the conventional system, the passive system offers a redundant operating mode for continued operation at reduced loads. Besides, the minimization of required convective heat transfer (e.g., ram air effect) about the components for supplemental cooling enables creative vehicle component placement options and optimizations.

Throughout this research, several cooling system architectures are introduced for electric vehicle thermal management. Each design is followed by a mathematical model that evaluates the steady-state and transient thermal responses of the integrated heat load(s) and the developed cooling system. The designs and the mathematical models are then validated through a series of thermal tests for a variety of driving cycles. Then, the cooling system design configuration is optimized using the validated mathematical model for a particular application. The nonlinear optimization study demonstrates that a 50\% mass reduction could be achieved for a continuous 12kW heat-dissipating demand while the electric motor operating temperature has remained below 65 centigrade degrees. Next, several real-time controllers are designed to engage the active cooling system for precise, stable, and predictable temperature regulation of the electric motor and reduced power consumption. A complete experimental setup compares the controllers in the laboratory’s environment. The experimental results indicate that the nonlinear model predictive control reduces the fan power consumption by 73% for a 5% increase in the pump power usage compared to classical control for a specific 60-minute driving cycle.

In conclusion, the conducted experimental and numerical studies demonstrate that the proposed hybrid cooling strategy is an effective solution for the next generation of electrified civilian and combat ground vehicles. It significantly reduces the reliance on fossil fuels and increases vehicle range and safety while offering a silent mode of operation. Future work is to implement the developed hybrid cooling system on an actual electric vehicle, validate the design, and identify challenges on the road.



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