Analysis of convection enhancing complex shaped adsorption vessels

Abstract

This work focuses on studying the adsorbent vessel external shape influences on the air surrounding the tank and, consequently, affecting the heat exchange by convection, hence passively increasing the system efficiency. Many studies in the literature focus on improving the adsorbent vessels interior and aspect ratio. However, a new approach is explored herein, the improvement on the external vessel geometry aiming to enhance the heat exchange by convection due the flow caused by its own generated heat. Then, by managing the heat generated by adsorption chemical reaction and converting it to air mass displacement, the vessel is improved without external energy sources. This study scientific contribution is to present an approach for an adsorbent tank model. The approach consists in coupling the dynamics of external air fluid and adsorption in the vessel interior, which is capable of generating a heat transfer coefficient that depends on geometry. The problem is divided into two domains and solved via the Finite Element Method. For the adsorbent domain, the equations are presented. Both domains are tied via the conduction heat transfer in the vessels wall. Several different designs are presented and exposed to an adsorption charging cycle. Methane is stored in an activated carbon bed. Results are presented, by comparing the temperature fields between the designs and the velocity fields as well as the amount of exchanged heat between the vessel wall and the external media. The value of the heat transfer coefficient is plotted on the designs walls for comparison. Additionally, the conventional approach (fixed h) and the variable h approach are compared. Results suggest an optimisation regarding the vessel external geometry is promising. This method allows measuring the improvement of adsorption systems by improving the natural convection due the external geometry, hence passively improving its efficiency (adsorption rate) and reducing its operational cost (when compared to active methods, such as heat exchangers) or its capacity (total amount of stored gas).