| In the field of space engineering, PEMFC (Proton exchange membrane fuel cell) with the membrane of polystyrene was firstly applied to GEMINI space missions of NASA (National Aeronautics and Space Administration). Since 1990s, the AFC was replaced by PEMFC gradually in the space mission application due to both the breakthrough of PEMFC in technologies and the disadvantage of AFC. PEMFC is the prospective candidates as power sources for space application with short-term missions due to the characteristics including: high energy conversion efficiency, zero emission, low temperature, regenerative operation etc.A significant technical challenge in PEMFC applied operation is the liquid management. All the studies of the two-phase flow dynamic inside PEMFC and it's effect on cell performance mentioned above were performed in the earth environment (normal gravity), however, it seems that no publication reports the liquid water transport and dynamic characteristics inside PEMFC in micro-gravity environment until now. In microgravity condition, the liquid/gas fluid flow is great different from that in normal gravity condition due to the absence of the gravity. Therefore, PEMFCs will show distinct behaviors in the reduced gravity environment because both the two phase flow dynamic inside PEMFC and cell performance are different. The study of fluid flow dynamic inside PEMFC and cell performance under the micro gravity condition will supply the approach for the reference of PEMFC operating characteristics and the liquid management in reduced gravity environment, for example in the space.First of all, in this study, the basic mathematic model for liquid water mass transport inside the PEMFC was built. The liquid water transport and two phase flow dynamic characteristic was studied both theritically and experimentally.Secondly, in this study, a noval, compact transparent PEMFC was designed, and the PEMFC operating characteristics with a single serpentine channel in a short-term micro gravity environment based on the 3.6s drop tower in the National Microgravity Laboratory, Institute of Mechanics, Chinese Academy Sciences, were performed.At last, in this study, a mathematical model of annular film condensation in the flow channel of PEMFC was developed, and the mathematical model was resolved numerically by MATLAB. The results of two phase flow characteristic parameter to predict the shape of the gas-liquid interface were obtained.The main work and results of this study are presented as the following:1. An extensive review on the direct visual study of two phase flow dynamic inside PEMFC by the aid of transparent PEMFC in normal gravity condition was summarized.2. The dynamic characteristic of liquid water in the flow channel of PEMFC was studied theritically and experimentally. The basic mathematic model for liquid water mass transport inside the PEMFC was built, and the critical curve to separate the single phase zone and the two phase flow zone depending on the liquid water condensation were obtained. The effects of oxygen flow rate, operating temperature, and cell orientation on the cell performance were studied experimentally.3. A PEMFC test system was designed for the study of two phase flow dynamic inside PEMFC under short-term micro gravity condition. The power system and driver circuit of the test system were successfully connected to the control system of drop capsule. The test system includes: reactants supply system, excess reactant gas release system, liquid recovery system, cell temperature controller unit, data acquisition and control system, and high-speed video recording system. A group of LEDs (light-emitting diode) was employed to meet the lighting requirement for captureing images. The power circuit and driver circuit of test system were designed.4. A noval, compact transparent PEMFC was designed in this study. A good design transparent fuel cell can reflect the real transport process inside practical operating PEMFCs. Verification of the screw and rod of bolts was performed to confirm the strength of bolts.5. The study on the effect of gravity level on the two phase flow dynamic inside PEMFC and cell performance of PEMFC with the vertical orientation configuration was performed. The results showed that when the load with resistant of 0.01? was connected to the fuel cell, the water production was high. The accumulated liquid water in the vertical parts of flow channel was removed easily by the reactant gas in the micro gravity environment. The cell performance was enhanced dramatically in the micro gravity condition because the flooded area in the flow channel was exposed to the reactant gas again. While, when the load with resistant of 0.03? was conneted to the fuel cell, the water production was low. In the micro gravity condition, the liquid water was removed upward by the gas phase due to the absence of gravity. But the effect on the liquid water dynamic and cell performance was not coincident. The results also showed that the more the gravity level changed, the more the cell performance was influenced.6. The study on the effect of gravity level on the two phase flow dynamic inside PEMFC and cell performance of PEMFC with the horizontal orientation configuration was performed. The results showed that little liquid water was found in the horizontal orientation configuration flow channel, and the water columns to pinch off the flow channel were difficult to be formed. In micro gravity condition, the water droplets departure diameter increased. The liquid water formed during the micro gravity condition duration was prone to stay in the flow channel, therefore, the cell performance was deteriorated due to the liquid water flooding in the flow channel in the micro gravity condition. A hyper gravity condition with the gravity of about 15g was induced when the drop capsule fell into the recovery string bag. The results also showed that the hyper gravity effect change the proton transport direction lead to a dynamic of current decreasing and voltage increasing.7. A mathematical model of annular film condensation in the flow channel of PEMFC was developed in this study, and the mathematical model was resolved numerically by MATLAB. The results of two phase flow characteristic parameter to predict the shape of the gas-liquid interface were obtained. The results showed that the length of two phase flow regime was influenced by the surface tension, the gas flow rate and equivalent diameter of flow channel. The length of two phase flow regime decreased with the decreasing of equivalent diameter; the length of two phase flow regime increased with the increasing of gas flow rate; and the length of two phase flow regime increased with the increasing of surface tension. The results also showed that the condensation was influenced by the cell temperature and environmental temperature. Increasing the cell temperature accelerated the condensation and enhanced the heat transport; increasing the environmental temperature reduced the condensation and reduced the heat transport.
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