Optimization Design And Performance Analysis For Energy System Of Proton Exchange Membrane Fuel Cell

Generally, proton exchange membrane fuel cell (PEMFC) produces a considerable amount of heat in the process of electrochemical reaction. The produced heat needs to be removed from the cell to prevent the membrane from dehydration and overheating. In this process of energy conversion, an important issue must be observed in that PEMFC usually operates at a temperature of about 70℃. Such a low temperature makes it difficult to use reaction heat for secondary utilization by conventional techniques. As a result of the recent development of modern renewable energy conversion technologies, some effective methods can be adopted to extract the low-temperature heat to satisfy the requirement of heat application. Through technology combination, these unique PEMFC systems not only improve the overall efficiency, but also achieve the resonable energy utiliztion according to energy grades. Based on the above idea, this thesis describes the different practical systems as typical examples of combined heat and electricity PEMFC system at different scales. The main researches are summarized as follows:1. A new power system that combines heat and electricity in a miniature PEMFC is introduced to improve the overall power efficiency in an underwater glider. It utilizes the available heat energy for navigational power of the underwater glider while the electricity generated by the miniature PEMFC is used for the glider's electronic devices. Experimental results show that the performance of the thermal engine can be obviously improved due to the high quality heat from PEMFC. Moreover, the heat-to-power ratio of PEMFC can be effectively altered to satisfy the navigational requirement of the typical glider by the change of operating conditions.2. Three typical types of fuel cell-battery hybrid powertrains are introduced for future fuel cell hybrid electric vehicle (FCHEV) designs. The purpose is to assess the potential benefits for different types of powertrains in energy efficiency, fuel economy and driving cost, which are the key factors to economic viability of FCHEV. Moreover, thermoelectric generator (TEG) is presented to integrate the PEMFC system by recovering the waste heat from the PEMFC to generate electricity for Li battery charging. Experiment results show that this technology combination can contribute to the improvement of overall efficiency and the size reduction of the Li battery.3. A gradational thermal energy system is presented for the distributed power generation, which utilizes the heat from the PEMFC to generate secondary electricity by employing the"Ocean Thermal Energy Conversion"(OTEC) technology, except for heating space. Exergy analysis is performed to illustrate the improvement in the performance of the TEC subsystem by using the comparatively high quality waste heat from the PEMFC. Simulation results show that the PEMFC and the TEC subsystems are interrelated through the change of the temperature. Specifically, the power output and generating efficiency of the TEC subsystem both show a nonlinear function of temperature.