Study On Two-Phase Flow And Resistance Characteristics In Liquid-feed Direct Methanol Fuel Cells

Direct Methanol Fuel Cell (DMFC) has become one of the most promising portable powers because of the advantages of methanol, such as its rich source, cheap prices, easy carrying and storage. Research of DMFC is concentrated on the environment more than60centigrade at home and abroad. Tools such as notebook, mobile phones and PDA with a portable power of DMFC are generally used at room temperature, so it’s necessary to carry out research on DMFC performance at ambient temperature.The liquid-feed DMFC at ambient temperature is the object of this study. Main work of this paper is listed below:A visualization liquid feed fuel cell designed and assembled. Test system of the fuel cell is established and debugged. Activated research is done on the membrane electrode assembly of DMFC. Effect of the structure of anode and cathode flow field on DMFC performance is analyzed. Research on resistance characteristics of the DMFC anode is done. The main conclusions are as follows:1. Activated research on the membrane electrode assembly of DMFC. Three different activation methods are used for the activation of membrane electrode. The effect of activation parameters,(such as activation time, activation medium and activation discharge current on the performance of DMFC) is analyzed. It can be concluded that performance of the battery is significantly improved if membrane electrode assembly is activated. Although ordinary wetting activation, acid activation and discharge activation all can achieve the best performance of membrane electrode assembly, the time of the three methods cost differs. Ordinary wetting activation requires four hours longer than two hours that acid activation and discharge activation require. Discharge activation of small current density can achieve the best performance of membrane electrode. Discharge activation of large current density will decline the performance of membrane electrode assembly.2. Effect of the structure of anode and cathode flow field on the performance of DMFC. Battery performance is tested when anode and cathode are parallel flow field, serpentine flow field or interdigitated flow field. Visualization research is done on carbon dioxide bubbles from the anode and droplets from the cathode. Effect of the structure of anode and cathode flow field on DMFC performance is analyzed. The experimental results show that serpentine How field performances better at anode flow field since carbon dioxide bubbles are easier to discharge, while carbon dioxide bubbles may block the flow channel in the parallel flow field and interdigitated flow field, which will affect the transmission of methanol. As a result, serpentine flow field is selected as the anode flow field of DMFC. For the cathode flow field, it was found that water drops blocked the flow channels in the parallel flow field. The long flow channel of serpentine flow field could easily lead to uneven distribution of oxygen and decline the battery performance. Because of its special structure of the flow channel assurance of sufficient supply of oxygen, battery performance achieves best results when interdigitated flow field is selected as the cathode flow field of DMFC.3. Characterization of flow resistance in the anode flow field was experimentally studied. Firstly, the experiment on two-phase flow resistance characteristics in anode of liquid-feed DMFC is done. Three different flow field is used to assembled transparent liquid feed DMFC. The effect of methanol flow rate, methanol concentration, flow field and current density on the pressure drop in anode is analyzed. It can be concluded that at low methanol flow rate, the pressure drop enhances at first, and then decreases and eventually becomes stable with increasing current density. Methanol concentration had a significant influence on the cell performance and a less effect on the pressure drop. The pressure drop in serpentine flow field is larger than that in parallel flow field and interdigitated flow field under the same operating condition. With the increase of the methanol solution flow rate, pressure drop in serpentine increases, which is larger than that in parallel flow field and interdigitated flow field. Secondly, the numerical model of the two-phase flow resistance characteristics in the anode channel of liquid-feed DMFC is established. Correctness of the model is validated by comparison with experimental results. The eflect of methanol flow rate, methanol concentration and current density on the pressure drop in anode is analyzed. It can be concluded that with the increase of the current density, gravity pressure drop decreases; frictional resistance and local resistance pressure drop increases, while accelerated pressure drop is substantially constant. At low methanol flow rates, gravity pressure drop plays a dominant role in the total pressure drop, so the total pressure drop decreases. With the increase of the methanol solution flow rate, frictional resistance and local resistance pressure drop play a dominant role in the total pressure drop, so the total pressure drop rises.