| Micro Direct methanol fuel cell (μDMFC) is considered as a promising power source candidate for portable electronic applications due to its advantages such as no need recharging, friendly to environment, simple structure and convenience for fuel carrying and store. In recent years, MEMS technologies used in the μDMFC have greatly promoted the miniaturization of the μDMFC. However, the performance of μDMFC is still far too low compared with that of the conventional DMFC. The block of reactant transportation induced by the CO2bubbles in micro flow field is one of the key factors affecting the μDMFC performance. Hence the development of methodologies to characterize the gas-liquid transportation, and then to mitigate the two-phase CO2-methanol block in the anode flow field, are vital for improving the μDMFC performance. In this thesis, a novel design by using the concept of the non-equipotent flow field, aiming to restrain the block effect of the CO2bubbles in the anode micro flow field, is proposed and investigated. The flow field designs were based on the theoretical and experimental gas-liquid characteristic results from the single bubble to the two-phase flow in the flow field channel.Single bubble behaviors when it departing from the carbon paper and moving in the channel were studied. A model describes the bubble departure diameter, which takes the gas flow rate, micro porous diameter and other parameters into account was established and validated. Force analysis of a single bubble in channel shows that the bubble tends to move toward the side with increasing cross-section dimensions of the channel, mainly because of the different surface tension at the two ends of the single bubble. This conclusion provides a theoretical basis for the design of a non-equipotent flow field. Moreover, a formula to determine the gas-liquid pressure drop in a rectangular micro channel was derived from a separated-phase flow model. The influences of the channel depth and its taper, as well as the liquid and gas flow rate, on the pressure drop of the channel, were also obtained by using this formula. Experimental results of the pressure drop in single straight-channels with different shape and depth shows that the pressure drop in gradually expand flow channel is higher than that in equipotent channel under the same liquid and gas flow rate. This result is consistent with that of the theoretical models. An in situ image experiment also shows a more smooth bubbles motion in a single straight-channel with expand cross-section than that in the conventional channels. This phenomenon is also can be found in the simulation results of the bubbles behavior in a complete flow field.Polymer flow field plates with non-equipotent flow channel was designed and fabricated with UV-LIGA techniques. Accuracy controlling method for the dimension of electroformed coating of the hot-pressing mould was proposed using a so call isolated-band process. Experimental results show that the accuracy of the electroformed coating dimension can be significantly improved by using this technique. For example, the relative errors of the cast layer dimensions of the straight channel are decreased from17%to7%during the electroforming of a nickel mold. On the other hand, the width error of cast layer of straight channel and bend channel in the mold is measured to be1.2%and3.8%, respectively. Hot pressing for the structures with high depth and dense layout features were also studied experimentally. It shows that a higher demold temperature is propitious to the automatic release of the hot-pressing substrate and to obtain a high replication accuracy of the flow channels. Finally, by fabricating a metal conductive layer and then bonding it with the polymer flow field plate, a new polar plate was successfully fabricated. In this process, photoresist buffer layer was used as the bonding agent to achieve reliable sealing between the conductive layer and flow field plate.Polymer μDMFC with non-equipotent flow field in anode were design, manufactured and tested. Effects of the channel shape, channel depth and the rid width on the gas-liquid transportation as well as the μDMFC performance were studied. Spectrum analyses for the transient pressure drop in flow channels, combined with the in situ image experiments of the gas-liquid transportation, were also implemented. Findings from the above researches show that the oscillation amplitude of the pressure drops both in flow fields with gradually expand or convergent channel cross section were less than that of the equipotent flow fields under the same current density. Flow fields with gradually expand channel can mitigate the clogging phenomenon of the CO2bubble in the flow channel, and thus improve the performance of the μDMFC. Peak power densities of the μDMFC equipped with flow field plates with expand and convergent channels were36%and19%higher respectively than that equipped with equipotent flow field. Effect of the rid width on the μDMFC performance equipped with expand flow channel was investigated. Results show that there exists an optimal rib width for CO2remove and for the fuel cell performance. Under the experimental conditions of this thesis the optimal rid width of800μm was achived. Experimental results for effect of the flow channel depth also shows that the increasing of the channel depth is beneficial for the remove of CO2bubbles. Accordingly, when the rid width of expand channel is800μm, the peak power density of μDMFC with expand channel depth of800μm is19.9%higher than that with expand channel depth of400μm.
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