Effect of bipolar-plates design on corrosion,mass and heat transfer in proton-exchange membrane fuel cells and water electrolyzers:A review

Attaining a decarbonized and sustainable energy system,which is the core solution to global energy issues,is accessible through the development of hydrogen energy.Proton-exchange membrane water electrolyzers(PEMWEs)are promising devices for hydrogen production,given their high efficiency,rapid responsiveness,and compactness.Bipolar plates account for a relatively high percentage of the total cost and weight compared with other components of PEMWEs.Thus,optimization of their design may accelerate the promotion of PEMWEs.This paper reviews the advances in materials and flow-field design for bipolar plates.First,the working conditions of proton-exchange membrane fuel cells(PEMFCs)and PEMWEs are compared,including reaction direction,operating temperature,pressure,input/output,and potential.Then,the current research status of bipolar-plate substrates and surface coatings is summarized,and some typical channel-rib flow fields and porous flow fields are presented.Furthermore,the effects of materials on mass and heat transfer and the possibility of reducing corrosion by improving the flow field structure are explored.Finally,this review discusses the potential directions of the development of bipolar-plate design,including material fabrication,flow-field geometry optimization using threedimensional printing,and surface-coating composition optimization based on computational materials science.

Impact of Magnetic Field on a Peristaltic Flow with Heat Transfer of a Fractional Maxwell Fluid in a Tube

Magnetic field and the fractional Maxwell fluids’impacts on peristaltic flows within a circular cylinder tube with heat transfer was evaluated while assuming that they are preset with a low-Reynolds number and a long wavelength.Utilizing,the fractional calculus method,the problem was solved analytically.It was deduced for temperature,axial velocity,tangential stress,and heat transfer coefficient.Many emerging parameters and their effects on the aspects of the flow were illustrated,and the outcomes were expressed via graphs.A special focus was dedicated to some criteria,such as the wave amplitude’s effect,Hartman and Grashof numbers,radius and relaxation–retardation ratios,and heat source,which were under discussions on the axial velocity,tangential stress,heat transfer,and temperature coefficients across one wavelength.Multiple graphs of physical interest were provided.The outcomes state that the effect of the criteria mentioned beforehand(the Hartman and Grashof numbers,wave amplitude,radius ratio,heat source,and relaxation–retardation ratio)were quite evident.

Numerical simulation of diffusion process for oxidative dehydrogenation of butene to butadiene

A comprehensive single particle model which includes the mesoscale and microscale models was developed to study the influence of particle diameter on mass and heat transfer occurring within a ferrite catalyst during the oxidative dehydrogenation of butene to butadiene process. The verified model can be used to investigate the influence of catalyst diameter on the flow distribution inside the particle. The simulation results demonstrate that the mass fraction gradients of all species, temperature gradient and pressure gradient increase with the increase of the particle diameter. It means that there is a high intraparticle transfer resistance and strong diffusion when applying the large catalysts. The external particle mass transfer resistance is nearly constant under different particle diameters so that the effect of particle diameter at external diffusion can be ignored. A large particle diameter can lead to a high surface temperature, which indicates the external heat transfer resistance. Moreover, the selectivity of reaction may be changed with a variety of particle diameters so that choosing appropriate particle size can enhance the production of butadiene and optimize the reaction process.

Field synergy analysis of different flow patterns in falling-film dehumidification system with horizontal pipes

Effects of the flow pattern of intertubular liquid film on mass and heat transfer synergies in a falling-film dehumidification system with horizontal pipes are studied.A flow model of the dehumidifying solution between horizontal pipes is established using Fluent software,the rule of transitions of the flow pattern between pipes is studied,critical Reynolds numbers of flow pattern transitions are obtained,and the accuracy of the model is verified by experiments.The mass transfer synergy angle and heat transfer synergy angle are respectively used as evaluation criteria for the mass transfer synergy and heat transfer synergy,and distribution laws of the synergy angles for droplet,droplet columnar and curtain flow patterns are obtained.Simulation results show that the mass transfer synergy angles corresponding to droplet,droplet columnar and curtain flow patterns all rise to a plateau with time.The mean mass-transfer synergy angle is 98°for the droplet flow pattern,higher than 96.5°for the droplet columnar flow pattern and 95°for the curtain flow pattern.The results show that the mass transfer synergy of the droplet flow pattern is better than that of the droplet columnar flow pattern and that of the curtain flow pattern.

Numerical Study on Surface Wettability Gradient Enhanced Ultra-Thin Loop Heat Pipe

Loop heat pipes(LHPs),as high-efficiency heat dissipation components,are considered to be superior thermal conductors beyond any known materials.To apply LHPs to mobile electronics,a small,thin and compact system needs to be designed.However,with the trend of miniaturization,the heat transfer performance of LHPs degrades rapidly due to the significant increase of working fluid backflow resistance.This work aims to propose an effective solution to this problem.In this work,the surface wettability gradient(SWG)is introduced into the ultra-thin LHP,and the influence of SWG on mass and heat transfer performance is studied comprehensively by using a transient three-dimensional numerical model.It is observed that the SWG can significantly increase the vapor-liquid circulation efficiency and improve heat transfer performance.Numerical experiments have been performed to compare the two kinds of LHPs with and without SWG.At the heat load of 4–6 W,the start-up time for LHP with SWG is shortened by 11.5%and the thermal resistance is reduced by about 44.3%,compared with the LHP without SWG.This work provides a solution for the performance-degradation problem caused by miniaturization,as a numerical reference for experiments.