A novel design for fin profile in metal hydride reactor towards heat transfer enhancement: Theoretical derivations and analysis

Hydrogen storage using metal hydrides is one of the research hotspots in the field of energy storage. However, metal hydride powders are known to have low thermal conductivity, which causes significant temperature fluctuation and hinders further reaction, hence efficient thermal management is a must for hydrogen storage using metal hydrides. In this paper, based on the principle of entransy dissipation, the optimal profile of fin in a cylindrical reactor under steady-state conditions is deduced. The expression for the temperature distribution of the bed is also obtained, which could clearly account for the influences of multiple involving factors, such as fin thickness, fin spacing, and radius of reactor. Through simulation, the characteristic time of hydrogen absorption for reactor inserting the optimized fin, is shortened by 19.1 % compared with the conventional uniform thickness fin. The influence of the geometric parameters of storage reactor was further discussed. When the ratio of the inner and outer radius of the reactor is confined (r_r/r_t≤2), linear thinning fin can be seen as a reasonable simplification of the optimized fin with comparable heat transfer enhancement effect. This study proves that the thermal management of metal hydride reactors, particularly those inserting high thermal conductivity materials like graphite, can be optimized quantitatively by entransy theory.