Date of Award


Document Type


Degree Name

Doctor of Philosophy (PhD)


Mechanical Engineering

Committee Chair/Advisor

John Wagner

Committee Member

Kapil Chalil Madathil

Committee Member

Richard Miller

Committee Member

Todd Schweisinger


The design of the automotive cooling systems has slowly evolved from engine-driven mechanical to computer-controlled electro-mechanical components. With the addition of computer-controlled variable speed actuators, cooling system architectures have been updated to maximize performance and efficiency. By switching from one large radiator to multiple smaller radiators with individual flow control valves, the heat rejection requirements may be precisely adjusted. The combination of computer regulated thermal management system should reduce power consumption while satisfying temperature control objectives. This research focuses on developing and analyzing a multi-radiator system architecture for implementation in ground transportation applications. The premise is to use a single radiator during low thermal loads and activate the second radiator during high thermal loading scenarios. Ground vehicles frequently use different radiators for each component that needs cooling (e.g., engine blocks, electronics, and motors) since they have different optimal working temperatures. The use of numerous smaller heat exchangers adds more energy-management features and alternative routes for carrying on with operation in the event of a crucial subsystem failure. Moreover, despite cooling systems being designed for maximum thermal loads, most vehicles typically operate at a small fraction of their peak values.

To study and examine the planned multi-heat exchanger cooling system concepts, various computer simulations and experimental tests were performed. A nonlinear state space model, featuring input and output heat flow paradigms, was developed using a multi-node resistance-capacitance thermal model. The heat removal rate from the radiator(s) was estimated using the -NTU method as downstream fluid temperatures were not required. The system performance was studied for two driving cycles proposed by the Environmental Protection Agency (EPA) – urban and highway driving schedules. The computer simulation was validated using the laboratory setup in the High Bay Area of Fluor Daniel Engineering Innovation Building. The configuration features computer controlled variable speed electric motor driven coolant pump and independent variable speed fans for each radiator to provide desired fluid flow rates. The pump and fan power consumptions are approximately 0.8-1.2 kW and 0.4-3.2 kW, which corresponds to coolant and air flow rates of 0.2-1.5 kg/s and 0.5-1.75 kg/s, respectively. Two servo motor-controlled gate valves limit the coolant outlet from each radiator. Various thermocouples and a magnetic flow sensor record test data in real time using a dSpace DS1103 data acquisition control system.

Designing and analyzing a nonlinear control architecture for the suggested system was the last phase in the study process. A nonlinear controller equipped TMS should offer higher energy efficiency and overall system performance. Three controllers—sliding mode, stateflow, and classical—were designed and implemented in Matlab/Simulink and placed onto the dSpace hardware. The sliding mode controller is recommended for high performance applications since it offers steady temperature tracking, 5oC, an acceptable response time, 120 sec, but suffers from frequent changes in fan speed. The stateflow controller exhibited the fewest fan speed oscillations, the fastest response time, 88 sec, and the smallest temperature offset, 3oC, it is advised for use in common passenger vehicle applications. Both controllers need around six minutes to warm up. The traditional controller, meanwhile, had the quickest warmup, 600 sec, but the slowest response time, 215 sec. Nonlinear cooling systems are essential for maintaining component temperatures which will enable vehicle reliability, and maximize performance given the focus on hybrid and electric vehicles.

Author ORCID Identifier




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