Numerical Simulation Of A Novel Composite Membrane For Hydrogen Separation

Due to the high heat of combustion, environmental friendly characteristic andmany other advantages, hydrogen could be directly used not only for automobiles, ships,spacecraft, and rocket engine, but also for centralized power plant and distributed powerplant such as fuel cells. Therefore, hydrogen has been considered as an extremelyexcellent new energy carrier. Since the fuel reforming reaction could transform thehydrogen fuel such as coal, gasoline, diesel oil and nature gas into the mixture ofhydrogen gas, the thermochemical method has become a dominant process to producethe hydrogen at a large scale in the world. Unfortunately, since the by-products ofthermochemical process of hydrogen fuel contain some harmful gas such as carbonmonoxide, which will decrease the catalyst activity and reduce the efficiency of fuel cell,the products of thermochemical process could not be directly adopted by the fuel cellssuch as PEMFC and this has become the dominant barrier for the real engineeringapplications of high efficiency, environmental friendly fuel cells. Therefore, it isnecessary to obtain the pure hydrogen gas from the products of thermochemical processand supply these high purity hydrogen for the fuel cells and other hydrogen consumeddevices.Since the palladium membrane has unique hydrogen selective characteristic, itcould be coupled in the production process of hydrogen and the high purity hydrogengas will be produced. Because the palladium is a kind of precious metal, the cost of purepalladium membrane is usually very high and it has limited the wide application ofmetal palladium membrane to produce high purity hydrogen. Since the cheap metal ofvanadium, tantalum and niobium have the similar hydrogen selective characteristics aspalladium, the cost of composite membrane of vanadium, tantalum, niobium andpalladium medal will be greatly decreased as compared to that of pure palladiummembrane. Therefore, the research of composite metal hydrogen membrane attracts alot of attentions in the recent years. However, due to the different coefficients of thermalexpansion between the base material and surface material for the composite membrane,the performance and service life of conventional membrane will be highly decreasedwhen the working temperature of membrane varies between low temperature and hightemperature.Due to the drawbacks of conventional plate membrane, this thesis proposed a unique embedded structure for the composite metal hydrogen membrane. Theperformances of hydrogen transportation were conducted under the condition ofdifferent structure parameters and fluid flow conditions. The simulation results showthat the performance of hydrogen transportation will be decreased for a given structureparameters of composite membrane when the inlet velocity of mixed gas increases; andthe rectangular structure of membrane have better hydrogen separation performancethan that of membrane with semi-ball structure due to the better disturbance effects tothe fluid flow. Based on the previous analysis, a new special structure of compositehydrogen membrane is proposed and the corresponding hydrogen transportationsimulations have been conducted. The simulation results show that the proposed newembedded structure of composite hydrogen membrane has better hydrogen separationperformance that that of conventional membrane. On the other hand, the thermalanalysis of composite membranes has been conducted. The simulation results show thatthe proposed new special structure of composite hydrogen membrane has much bettercharacteristics in terms of service life as compared to that of conventional platecomposite membrane. Therefore, the research results of this thesis could provide someconstructive data to product the high hydrogen separation performance and long servicelife for a composite metal membrane.