Development Of A Thermal-Mechanical Fatigue Testing System For MEMS-based Fuel Cells

MEMS (Micro-Electro-Mechanical Systems, MEMS)-based fuel cell is a novel micro power source that combines the technologies of microfabrication and fuel cell manufacturing. It has many advantages such as high specific energy, high efficiency, easy to use, low pollution, etc. When the MEMS fuel cells are periodically started and stopped, the changes of the cell temperature and internal pressure from the reactants’flow may impose an alternating thermal-mechanical load in low-frequency on the package frame of the cell. This may subsequently cause the defects of creep and delamination in the package, increase resistance of the cell and finally lead to performance degradation or even fatigue failure of the cell. In order to provide an apparatus for the fatigue evaluation of the MEMS-based fuel cell, this paper develops a thermal-mechanical fatigue testing system for the MEMS-based fuel cell after load analysis. The works of this paper can be listed as follows:Firstly, the sources of thermal-mechanical loads of the MEMS-based fuel cell and its impacts on the cell performance are analyzed. In this research, the mechanical load impose on the fuel cell package is calculated by pressure drop characterization of the fuel/oxidant flow in flow bed of the cell during its running. Secondly, the working principle of the thermal-mechanical fatigue testing system is illustrated and the design of the system is specified. The temperature controlling module and the flow controlling module is developed respectively, and the fatigue testing system is integrated using the two modules. In this work, in order to speed up the response of the temperature controlling module, a novel heat exchanger with circulating pipe surrounding the testing sample is utilized. Thirdly, the control methodologies of the temperature/flow modules and its integration approaches, including the design of the controlling structure and controlling program in LabVIEW, are studied. Finally, the fatigue testing system is experimentally verified. Results show that for the temperature controlling module, the output temperature of the system is falled in the range of5-85℃, hence the experimental alternating temperature for the sample cell can be set to10-65℃.The rising and falling rate of the temperature is higher than5℃/min and5℃/min, respectively. The steady-state deviation of the target temperature is less than1℃.For the flow controlling module, the controllable range and controlling precision of the liquid in anode of the cell is0,1-99.9ml/h and±0.1ml/h, respectively. In the cathode side, the corresponding figure for the gas-flow controlling is0.2-100L/min and±0.1L/min. respectively. This means that the results meet the design requirements quite well. On the other hand, this fatigue testing system has also been used to evaluate the fatigue effects on the performance of a MEMS-based fuel cell. Results show that the internal resistance increases with the increase of cycle times of thermal-mechanical load, and the cell performance decline during this process until fatigue failure is finally occurred. The system developed in this paper can provide an experimental platform for thermal-mechanical fatigue evaluation of MEMS-based fuel cells with advantages such as small size, easy to operate, high efficiency, high security and reliability.