理想强边水驱油藏天然水体体积的简便计算

针对天然水体体积计算难题,从水侵量的定义公式出发,以S理想边水驱油藏为例,以廖运涛方法获得的精确解为约束条件,主要是对采用的综合压缩系数进行校正,获得了理想边水驱油藏天然水体体积的简便估算方法,在类似油藏上应用取得了好效果,为选择合适的开发方式提供了重要依据。对于井网完善、已全面投入开发、完全依靠边水补充能量、以自喷为主的高渗透、稀油油藏,在经历几年的开发后有明显的油层压降情况下,只要能够落实清楚总压降值和与之对应的水侵量,就可以估算出天然水体的体积。至于该方法能否拓宽应用范围,尚需进一步探讨。     

Mitigation of Water Management in PEM Fuel Cell Cathodes by Hydrophilic Wicking Microporous Layers

This study introduces a novel strategy for enhancing the performance of polymer electrolyte fuel cells at high current densities by means of an advanced gas diffusion layer design. The incorporation of hydrophilic wicking agents into microporous layers of the cathode gas diffusion layer improves water management, thus increasing the maximum power density of polymer electrolyte fuel cells. Ex situ measurements with respect to water and vapour transport, and electrochemical polarisation data provide evidence suggesting that the beneficial effect has to be attributed to enhanced liquid water removal through the microporous layer.     

Mathematical Model of Proton Exchange Membrane Fuel Cell with Consideration of Water Management

One‐dimensional model on the membrane electrode assembly (MEA) of proton exchange membrane fuel cell is proposed, where the membrane hydration/dehydration and the possible water flooding of the respective cathode and anode gas diffusion layers are considered. A novel approach of phase‐equilibrium approximation is proposed to trace the water front and the detailed saturation profile once water emerges in either anode or cathode gas diffusion layer. The approach is validated by a semi‐analytical method published earlier. The novel approach is applicable to the polarization regime from open circuit voltage to the limiting current density under practical operation conditions. Oxygen diffusion is limited by water accumulation in the cathode gas diffusion layer as current increases, caused by excessive water generation at the cathode catalyst layer and the electro‐osmotic drag across the membrane. The existence of liquid water in the anode gas diffusion layer is predicted at low current densities if high degrees of humidification in both anode and cathode feeds are employed. The influences of inlet relative humidity, imposed pressure drop, and cell temperature are correlated well with the cell performance. In addition, the overpotentials attributed from individual components of the MEA are delineated against the cell current densities.     

Development of a Self‐Adaptive Direct Methanol Fuel Cell Fed with 20 M Methanol

A passive and self‐adaptive direct methanol fuel cell (DMFC) directly fed with 20 M of methanol is developed for a high energy density of the cell. By using a polypropylene based pervaporation film, methanol is supplied into the DMFC's anode in vapor form. The mass transport of methanol from the cartridge to the anodic catalyst layer can be controlled by varying the open ratio of the anodic bipolar plate and by tuning the hydrophobicity of anodic diffusion layer. An effective back diffusion of water from the cathode to the anode through Nafion film is carried out by using an additive microporous layer in the cathode that consists of 50 wt.% Teflon and KB‐600 carbon. Accordingly, the water back diffusion not only ensures the water requirement for the methanol oxidation reaction but also reduces water accumulation in the cathode and then avoids serious water flooding, thus improving the adaptability of the passive DMFC. Based on the optimized DMFC structure, a passive DMFC fed with 20 M methanol exhibits a peak power density of 42 mW cm^–2 at 25 °C, and no obvious performance degradation after over 90 h continuous operation at a constant current density of 40 mA cm^–2.     

Dynamic Response of a Subsaturated Polymer Electrolyte Fuel Cell in Counterflow Mode

This work demonstrates that the operation of a subsaturated polymer electrolyte fuel cell in counterflow mode results in a significantly elongated relaxation time after a load change, if compared to coflow mode. This effect is investigated here by using combined dynamic locally resolved measurements of the current density, the high frequency resistance, and the relative humidity. It is shown that the elongated relaxation time is a consequence of slow membrane hydration in the region of the cell, downstream the anode flow field, where the diffusive flux of water across the membrane occurs from the anode to the cathode. Here, the anode gas stream, which is humidified upstream the anode flow field via back diffusion of water from the cathode to the anode, is the only source of water for both membrane hydration and the internal humidification of the cathode gas stream, which passes the cell in opposite direction.     

Effects of GDL Structure with an Efficient Approach to the Management of Liquid water in PEM Fuel Cells

A model fuel cell with a single transparent straight flow channel and segmented anode was constructed to measure the direct correlation of liquid water movement with the local currents along the flow channel. Water drops emerge through the largest pores of the GDL with the size of the droplets that emerge on the surface determined by the size of the pore and its location under the gas flow channel or under the land. Gravity, surface tension, and the shearing force from the gas flow control the movement of liquid in the gas flow channel. By creating a single large diameter pore in the GDL, liquid water flow emergent from the GDL was forced to be in specific locations along the length of the channel and either under the land or under the channel. The effects of gravity were amplified when the large pore was under the channel, but diminished with the large pore under the land. Current fluctuations were minimised when the dominant water transport from the GDL pore was near the cathode outlet. The results show that it is possible to engineer the water distribution in PEM fuel cells by modifying the pore sizes in the GDL.     

不同元件长径比对液液静态混合的影响

应用FLUENT软件对5种不同长径比的静态混合器进行液液两相混合的数值模拟,得出各混合密度云图、混合不均匀系数Ψ和压力降进行比较分析。进而得出以下结论,当混合元件长径比Ar从1.0逐渐增大到2.0时,从混合密度云图和混合不均匀系数Ψ值来看,在达到预期混合效果即Ψ值达到0.05时,所需的混合元件个数随着长径比Ar的增大而减小。所需混合长度L相差不大,约为混合管直径D的1~1.5倍,混合压降相差大约7倍。所以在混合管直径D不大的情况下,选取Ar=2.0的混合器则更理想,而且单纯依靠入口流速的变化并不能对混合效果产生太大影响。