Complete and reduced models for metal hydride reactor with coiled-tube heat exchanger

Abstract

Thermal effects during hydriding/dehydriding have a significant influence on the performance of metal hydride hydrogen storage system. The heat exchanger is widely used in the metal hydride reactor in order to improve the efficiency of system. In this work, based on mass balance, momentum balance, energy balance equations, equation of reaction kinetics and equilibrium pressure equation, a two dimensional axisymmetric model of metal hydride reactor packed with LaNi5 is developed on Comsol platform. The model is validated by comparing its simulation results with the experiment data and the simulation results from other works. Then, the straight pipe heat exchanger and the coiled-tube heat exchanger are taken into consideration in order to improve heat transfer from metal hydride reactor to ambient environment. The complete three dimensional model is developed for the metal hydride reactor equipped with the coiled-tube heat exchanger. The case with coiled-tube heat exchanger shows better efficiency than the other. In general, the temperature in central area is higher than others. In order to cool central area effectively, two designs of heat exchangers, including the combination of coiled-tube heat exchanger and straight pipe heat exchanger and the concentric dual coiled-tube heat exchanger, are studied. The results show that it is an effective method to improve the efficiency of metal hydride reactor by equipping dual coiled-tube heat exchangers. Reduced two dimensional model is applied to metal hydride reactor with coiled-tube heat exchanger to reduce computing time. The simulation results of reduced model generally agree with those of complete three dimensional model.