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排序方式: 共有477条查询结果,搜索用时 31 毫秒
1.
《International Journal of Hydrogen Energy》2022,47(37):16335-16346
Oxygen blocking the porous transport layer (PTL) increases the mass transport loss, and then limits the high current density condition of proton exchange membrane electrolysis cells (PEMEC). In this paper, a two-dimensional transient mathematical model of anode two-phase flow in PEMEC is established by the fluid volume method (VOF) method. The transport mechanism of oxygen in porous layer is analyzed in details. The effects of liquid water flow velocity, porosity, fiber diameter and contact angle on oxygen pressure and saturation are studied. The results show that the oxygen bubble transport in the porous layer is mainly affected by capillary pressure and follows the transport mechanism of ‘pressurization breakthrough depressurization’. The oxygen bubble goes through three stages of growth, migration and separation in the channel, and then be carried out of the electrolysis cell by liquid water. When oxygen breaks through the porous layer and enters the flow channel, there is a phenomenon that the branch flow is merged into the main stream, and the last limiting throat affects the maximum pressure and oxygen saturation during stable condition. In addition, increasing the liquid water velocity is helpful to bubble separation; changing the porosity and fiber diameter directly affects the width of pore throat and the correlative capillary pressure; increasing porosity, reducing fiber diameter and contact angle can promote oxygen breakthrough and reduce the stable saturation of oxygen. 相似文献
2.
《International Journal of Hydrogen Energy》2019,44(17):8807-8818
As hydrogen-air mixtures are flammable in a wide range of concentrations and the minimum ignition energy is low compared to hydrocarbon fuels, the safe handling of hydrogen is of utmost importance. Additional hazards may arise with the accidental spill of liquid hydrogen. Such a release of LH2 leads to a formation of a cryogenic pool, a dynamic vaporization process, and consequently a dispersion of gaseous hydrogen into the environment. Several LH2 release experiments as well as modeling approaches address this phenomenology. In contrast to existing approaches a new CFD model capable of simulating liquid and gaseous distribution was developed at Forschungszentrum Jülich. It is validated against existing experiments and yields no substantial lacks in the physical model and reveals a qualitatively consistent prediction. Nevertheless, the deviation between experiment and simulation raises questions on the completeness of the database, in particular with regard to the boundary conditions and available measurements. 相似文献
3.
For the air feed in proton exchange membrane fuel cells (PEMFCs), the wave‐like gas channel (GC) shows obvious advantages over the straight GC because the former enhances collision of secondary flow and diffusion in the gas diffusion layer (GDL). However, it is prone to water flooding, which brings greater pressure drop, larger pressure oscillation, and blocking of reaction area. In the present study, numerical models of the water dynamic processes, including water droplets emerging from micropores on the GDL surface and removing through the GC, are established based on the volume of fluid (VOF) method. Water coverage ratio and pressure drop are calculated to evaluate the water flooding. The effects of the dimensional parameters of wave‐like GC and contact angle of channel walls on the water accumulation are studied. The emergence and removal of liquid water is a quasiperiodic and oscillating process. Multicycle simulations show that channel pressure drop increases linearly with greater growth rate than channel length. The equilibrium position of water droplet is strongly dependent on the relative wettability of the GDL and bipolar plate (BPP) surfaces. And the geometric parameters of GC have a significant impact on the pressure, water removal behavior and detachment time. Smaller bent angle brings bigger pressure drop, and larger cycle length is helpful for relieving the oscillation of pressure. 相似文献
4.
《International Journal of Hydrogen Energy》2021,46(59):30442-30454
In a proton exchange membrane fuel cell (PEMFC), effective GDL surface water elimination is significant to water management. This paper used the volume-of-fluid method (VOF) method to carry out simulation research on transferring liquid water in the flow channel with a hydrophilic pipe. The findings indicated that compared with a straight channel, a hydrophilic pipe structure could effectively remove water from the gas diffusion surface (GDL) and reduce the surface water coverage of the GDL. With the increase in the diameter and height of the pipe structure, the GDL surface's water coverage first increased and then decreased, and it was less with the pipe structure than with the direct flow channel. The removal rate of water on the GDL surface was accelerated. The spacing of hydrophilic pipes has a significant impact on the transportation of water. As the spacing increases, the removal rate of water on the GDL surface slowed. A hydrophilic pipe structure with a diameter of 75 μm, a height of 400 μm, and spacing of 300 μm has good water removal performance on the GDL surface. This research work proposes a new internal structure design of the flow channel, which has specific implications for removing water on the GDL surface. 相似文献
5.
Ali Hojeij Laurent Jossic Philippe Séchet Cyrille Bonamy Albert Magnin Stéphane Hattou 《American Institute of Chemical Engineers》2022,68(2):e17442
Mixing by gas injection is an operation used in industrial processes such as wastewater treatment, metallurgy, or methanization in which pressurized gas is injected into a fluid in order to reduce concentrations and temperatures gradients. This study demonstrates how the CFD toolbox OpenFOAM can be used to simulate such flows. Experimental measurements and observations have been performed on a pilot-scale reactor where pressurized air is injected in a yield stress fluid. The volume of fluid method and an adaptive mesh with refinement at the interface have been used to track the gas inclusions. The numerical model accuracy has been assessed by comparing experimental and numerical results related to the bubble's frequency, dimensions, and rising velocities as well as the fluid recirculation, yielded, and unyielded regions in the tank. The influence of injection parameters such as the injection flow rate and the fluid rheological parameters has been quantified. 相似文献
6.
7.
基于VOF界面追踪技术,建立了氧气转炉顶吹过程渣-金-气多相传输行为的数学模型,研究了渣-金-气三相界面行为,给出了渣/金界面特征的演化过程和熔池内流场变化特征,对冲击坑形态进行了具体的描述,并对穿透深度和冲击坑直径进行了定量化的表征。结果表明:由于冲击坑表面波的传播,冲击坑以及渣/金/气界面具有明显的瞬态特征且熔池是振荡的;钢液熔池内涡旋中心位置随着吹炼时间以及渣的运动而变化;低枪位加强了钢液表面的波动,增加了钢液表面的粗糙度,增大了射流与熔池的接触面积,从而有利于射流向熔池的动量传递,促进熔池的搅拌。 相似文献
8.
不同多相流模型在航行体出水流场数值模拟中的应用 总被引:1,自引:0,他引:1
基于VOF和Mixture两种均相流模型,并结合输运方程类空化模型、k-ε湍流模型和动网格技术,针对圆柱形航行体出水过程进行了数值模拟,获得了无空化、带空泡两种状态下航行体出水过程中的多相流物理景象和表面压力变化历程。根据计算结果分析了VOF模型、Mixture模型在多相流界面捕捉、压力计算等方面的异同,并给出了两种模型的适用范围,在理论研究和工程应用上都具有重要意义。 相似文献
9.