Thermal management and optimization of the reactor geometry for adsorbed natural gas storage systems subjected to free convection and radiative environment

Abstract

The present investigation explores the effects of the reactor geometry (i.e., the aspect ratio of cylindrical and annular reactors with and without fins, fin spacing, the aspect ratio of fins for finned reactors, and outer to inner diameter ratio for annular unfinned reactors) on the heat and mass transfer characteristics of the adsorbed natural gas storage system employing passive cooling techniques. The authors try to capture how the geometric modification changes the surrounding buoyancy-driven flow physics and improves the proposed novel reactor's storage performance. The study also considers surface radiation, which significantly improves the heat transfer rate, especially for the reactor with lower internal thermal resistance. An attempt is made to reduce the internal thermal resistance of the adsorbent bed by adding 10% graphite by mass and suitably modeling the bed's thermal conductivity and thermal capacity. The result shows that, in terms of adsorbed amount and heat transfer rate, the reactors with an aspect ratio (AR) of 7.8 outperform the other aspect ratios. The simultaneous effects of reactor aspect ratio and fins spacing on the heat transfer and adsorption rates are expounded, and the optimum fin spacing as a function of reactor aspect ratio and diameter ratio (i.e., fin diameter to reactor diameter) is obtained. The best annular reactor outperforms the cylindrical reactor with and without fin in terms of volumetric and gravimetric storage capacity. The annular finned reactor achieves a maximum 33% improvement in storage capacity compared to the adiabatic case and isothermal efficiency of 90%.