Gao, Xin

This thesis presents two case studies on improving the efficiency and the loadfollowing capability of a high temperature polymer electrolyte membrane (HTPEM) fuel cell system by the application of thermoelectric (TE) devices.TE generators (TEGs) are harnessed to recover the system exhaust gas for electricity. For this aim, a heat exchanger based TEG heat recovery subsystem is designed. Instead of optimizing an ordinary rectangular heat exchanger, high efficient and commercialized compact plate-fin exchangers are applied. A library of types of them is also included to pinpoint the ideal heat exchanger type. Commercially available TEG modules are chosen for the subsystem.To optimize the subsystem design, a numerical model was then built and validated. It is a model of several novel elements from the literature. To suit the desires of the subsystem design and operation studies, model precision, versatility and computational load are emphasized. Sensitivity analysis is introduced to master the characteristics of the subsystem and its major parameters for both design and operating considerations. The effects of a power conditioning method, such as Maximum Power Point Tracking (MPPT), of the subsystem power output on the subsystem design and performance were also systematically analyzed. The TEG subsystem configuration is optimized. The usefulness and convenience of the model are proved.TE coolers (TECs) are integrated into the methanol evaporator of the HT-PEM system for improving the whole system load-following capability. System efficiency can also be increased by reducing heat loss. Working modes of the integrated TEC modules are various and unique. They are redefined as TE heat flux regulators (TERs). The feasibility and merits of the TE-integrated evaporator are also identified by an own developed three-dimensional numerical model in ANSYS Fluent®.This thesis introduces the progress of this project in a cognitive order. The first chapter initially prepares the theory and characteristics of the fuel cell system and TE devices. Project motivations are conceived. Then similar studies existing in literature are reviewed for their experiences. Afterwards, the project road map is identified by a list of project objectives. The detailed considerations and steps during carrying out the project are addressed in the second chapter. Major innovations out of this project are also highlighted. The third chapter presents the main results and discussions. Conclusions and future work are discussed in the last chapter

HT-PEM Fuel Cell System with Integrated Thermoelectric Exhaust Heat Recovery

http://vbn.aau.dk/files/202044466/xin_gao.pdf

HT-PEM Fuel Cell System with Integrated Thermoelectric Exhaust Heat Recovery

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