PEMFC水淹的阳极气体压力降变化特征预警技术

通过观察阳极气体压力降对一个两片的质子交换膜燃料电池堆进行水淹预警的研究发现,其在水淹过程中阳极气体压力降具有'两级台阶'的变化特征。结合流道内水积聚过程的研究成果以及电压的变化特点,可以将水淹过程分为良好期、湿润期、过渡期和水淹期4个阶段。对比实验表明电流和温度对于两级台阶的相对幅度影响不大,气体压力和阳极过量系数对台阶相对幅度有较显著的影响。提高气体压力和增大阳极过量系数可以提高PEMFC抵抗水淹的能力,但增大阳极过量系数则会造成氢气浪费。调整电池堆工作温度是一种有效的水淹自愈手段,通过调整温度可以使PEMFC工作在'微湿未淹'的状态下。阳极脉冲排气或增大阳极气体过量系数则可作为PEMFC严重水淹时的辅助处理措施。

闭式循环柴油机旋转床吸收器气体压降模型

分析了闭式循环柴油机(CCD)旋转床CO2吸收器内气液流动特点,建立了流经碟片填料旋转床吸收器气体压降计算模型。通过实验及编程计算,得到了气体压降数学模型中实验关联系数值。经不同工况下气体压力降模型计算值与实验值对比,表明两者相对误差小于15%,可用于实际CCD系统旋转床CO2吸收器的优化设计。

Effect of nozzle geometry on pressure drop in submerged gas injection

Submerged gas injection into liquid leads to complex multiphase flow, in which nozzle geometries are crucial important for the operational expenditure in terms of pressure drop. The influence of the nozzle geometry on pressure drop between nozzle inlet and outlet has been experimentally studied for different gas flow rates and bath depths. Nozzles with circular, gear-like and four-leaf cross-sectional shape have been studied. The results indicate that, besides the hydraulic diameter of the outlet, the orifice area and the perimeter of the nozzle tip also play significant roles. For the same superficial gas velocity, the average pressure drop from the four-leaf-shaped geometry is the least. The influence of bath depth was found negligible. A correlation for the modified Euler number considering the pressure drop is proposed depending on nozzle geometric parameter and on the modified Froude number with the hydraulic diameter of the nozzle do as characteristic length.

A force transfer mechanism for triggering landslides during rainfall infiltration

Shallow slope failures induced by rainfall infiltration occur frequently, and the relevant triggering mechanisms have been widely studied.Rainfall-induced landslides are widely recognized to be caused by increases in soil weight, seepage force and pore water pressure or decreases in soil mechanical properties. However, even when all these factors are considered, some landslides still cannot be explained well. The increased pore water pressure in a slope reduces the effective stress of the soil and may trigger slope failure. Similarly, the pore gas pressure in a slope also reduces the effective stress of the soil but has been neglected in previous studies. As the viscosity of air is nearly negligible when compared with that of water, the pore gas pressure spreads faster, and its influence is wider, which is harmful for the stability of the slope. In this paper, the effects of pore gas pressure are considered in a shallow slope stability analysis, and a self-designed experiment is conducted to validate the force transfer mechanism.Numerical simulation results show that the pore gas pressure in the slope increases sharply at different locations under heavy rainfall conditions and that the pore gas pressure causes a rapid decrease in the slope safety factor. Laboratory experimental results show that the pore gas pressure throughout the whole unsaturated zone has the same value, which indicates that the gas pressure could spread quickly to the whole sample.

Modeling the pressure drop of wet gas in horizontal pipe

A model for gas–liquid annular and stratified flow through a horizontal pipe is investigated, using the two-phase hydrokinetics theory. Taking into consideration the flow factors including the void fraction, the friction between the two phases and the entrainment in the gas core, the one-dimensional momentum equation for gas has been solved. The differential pressure of the wet gas between the two tapings in the straight pipe has been modeled in the pressure range of 0.1–0.8 MPa. In addition a more objective iteration approach to determine the local void fraction is proposed. Compared with the experimental data, more than 83% deviation of the test data distributed evenly within the band of ± 10%. Since the model is less dependent on the specific empirical apparatus and data,it forms the foundation for further establishing a flow measurement model of wet gas which will produce fewer biases in results when it is extrapolated.

Reducing the Gas Pressure Drop in Suction Mufflers of Hermetic Reciprocating Compressors

The suction muffler of hermetic reciprocating compressors is installed in order to attenuate the noise generated by the gas pulsation of the flow through the suction valve. However, the installation of the suction muffler affects the operation of the compressor owing to gas pressure drop, which causes volumetric and energetic efficiency loss due to the gas specific volume augmentation. Therefore, there is a compromise between sound attenuation and pressure drop increase, which has to be taken into account by compressor designers. In this work, it presents a numerical solution to the flow through a suction muffler in order to analyze the pressure field and point out the main contributions to the overall pressure drop of the flow. A commercial CFD （computational fluid dynamics） code was used to perform the numerical simulations and the results were validated by using experimental data. After analyzing the pressure field, the geometry of the muffler was modified intending to decrease the flow pressure drop. The geometric modification produced a 28% reduction on the overall pressure drop, without influencing the sound attenuation.