Finite element simulation of heat and mass transfer in activated carbon hydrogen storage tank

Abstract

A mathematical model of heat and mass transfer in activated carbon (AC) tank for hydrogen storage is proposed based on a set of partial differential equations (PDEs) controlling the balances or conservations of mass, momentum and energy in the tank. These PDEs are numerically solved by means of the finite element method using Comsol MultiphysicsTM. The objective of this paper is to establish a correct set of PDEs describing the physical system and appropriate parameters for simulating the hydrogen storage process. In this paper, we establish an axisymmetric model of hydrogen storage by adsorption on activated carbon, considering heat and mass transfer of hydrogen in storage tank during the charging process at room temperature (295K) and the pressure of 10MPa. To simulate the hydrogen storage process accurately, the heat capacity of adsorbed phase, the contact thermal resistance between the AC bed and the steel wall and the inertial resistance of high speed charging hydrogen gas are all taken into account in the model. The governing equations describing the hydrogen storage process by adsorption are solved to obtain the pressure changes, temperature distributions and adsorption dynamics in the storage tank. The pressure reaches a maximum value of 10MPa at about 240s. A small downward trend appears in the later stage of the charging process, which lasts 700s. The temperature distribution is highest in the center of the tank. The temperature history exhibits a rapid increase initially, followed by a steady decline. A modified Dubinin–Astakhov (D–A) model is used to represent the hydrogen adsorption isotherms. The highest hydrogen uptake is 10molH2/kg AC, at the entrance of hydrogen storage tank, where the temperature is lowest. The adsorption distribution at a given time is mainly determined by the temperature distribution, because the pressure is almost uniform in the tank. The adsorption history, however, is dominated by the pressure history because the pressure change is much larger than temperature change during the charging process of hydrogen storage.