Design optimization, sensitivity analysis and operational comparison of a duplex helical elliptical tube metal hydride reactor

Abstract

Due to the strong exothermic/endothermic effect during the H₂ absorption/desorption process, the design of metal hydride reactors has become a hot research topic to improve the rate of hydrogenation/dehydrogenation. Herein, based on bionic optimization and the constructal theory, a novel duplex helical elliptical tube reactor (DHER) is proposed for enhancing the heat transfer and reaction performances of metal hydride reactors. DHER displayed outstanding performances among 5 types of reactors, and the maximal temperature difference could be reduced by 5.1 K/5.6 K during the H₂ absorption/desorption. The parameters of DHER were designed and optimized with the spiral diameter (D_c) = 10 mm, elliptical major axis (A) = 4 mm, elliptical minor axis (B) = 2 mm, pitch (P_t) = 13 mm, tilt angle (α) = 45°, and installation angle (β) = 180°. The sensitivity analysis for DHER is investigated, and the sequential effects of the structural parameters on the reaction performance followed the order of D_c > A > B > P_t > α. Through a comparative analysis of geometrical characteristics of the structural parameters and the reaction performance of the reactor, the results indicated that the radial projected area of the heat exchange tube is the dominant factor in the reaction performance of DHER. Moreover, the surface was calculated based on the sensitivity analysis data and fitted by the quadratic response surface regression model to predict the reaction time under different structural parameters, which may provide guidance for the design of reactors. In addition, the hydriding and dehydriding cyclic processes without preheating and precooling stages were confirmed to have prominent and reliable performances for DHER, attaining only 1227 s under its optimal cycle conditions during absorption (0.8 MPa, 273.15 K) and desorption (0.1 MPa, 373.15 K).