Numerical Simulation And Optimization Analysis Of Hydrogen Storage By Adsorption On Metal-organic Framework

As an emerging hydrogen storage technology,adsorptive hydrogen storage is considered to be the most promising hydrogen storage method due to its high hydrogen storage density,fast charge and discharge rate and safety.When the adsorption storage tank is filled with hydrogen,the heat of adsorption and the work of compression cause the temperature of the tank to rise and the adsorption effect is lowered.Hydrogen is more present in the gaseous form than in the adsorbed state,causing the tank pressure to rise.That is,the thermal effect during the inflation process causes the pressure to be too high,which increases the power consumption of the compressor and brings about safety problems.In the deflation process,on the contrary,the decrease in temperature makes hydrogen less desorptive and increases the residual amount in the tank.Therefore,it is necessary to study the charge and discharge characteristics of the canister.In this paper,COMSOL Multiphysics software was used to simulate the charge and discharge process of small adsorption tanks.Then,the inflation process was optimized.The specific work and results were as follows:Firstly,the research and development status of adsorption materials and adsorption hydrogen storage systems are introduced.Especially,activated carbon and metal organic framework materials have better hydrogen storage effects and more related research.Next,the simulation theory carried out in this paper was analyzed.The mass conservation,momentum conservation and energy conservation involved in the adsorption process were described.The calculation formulas of mass source and heat source term under adsorption conditions were given.In order to describe the adsorption behavior of hydrogen in porous materials,the adsorption theory,adsorption isotherms,calculation of adsorption heat and application of gas state equations were introduced.Then the flow field and temperature field were coupled to simulate the inflation and deflation process of MOF-177 dryo-adsorption hydrogen tank,and the trends of pressure,temperature and adsorption amount were obtained,which were compared with MOF-5.According to the results,the following conclusions were obtained: the replacement of adsorbent from MOF-5 to MOF-177 with better hydrogen storage performance will significantly reduce the maximum pressure during the aeration process and the equilibrium pressure after cooling;The center of the tank was less affected by the inlet and the environment,and the heat transfer effect was not good,resulting in the concentration of heat to form a high temperature zone,which seriously affected the adsorption effect.It can be seen from the mass balance that adsorptive hydrogen storage has considerable advantages at low temperatures.Finally,the optimization of the inflation process was carried out on the basis of the MOF-177 adsorption tank with the better performance.First,the rate of inflation was changed,a gradual decrease in flow rate resulted in a lower maximum temperature.Then,the thermal conductivity of the adsorbent was increased,and the inflation temperature rise and pressure rise were obviously improved,but the yield decreased as the thermal conductivity increases.Finally,the heat exchange fins were added.On the one hand,the original flow field in the tank was disturbed,and the speed was concentrated in the center of the tank,so that the influence of the inlet was increased and the low temperature zone was enlarged.On the other hand,the heat exchange structure was changed,and the temperature near the ribs was further lowered.