Numerical modelling and heat transfer optimization of large-scale multi-tubular metal hydride reactors

Heat management during the absorption/desorption process is a key aspect in improving the performance of large-scale hydrogen storage systems. In this article, the absorption and desorption performance of a multi-tubular hydride reactor is numerically investigated and optimized for 60 kg mass of LaNi5 alloy. The 90% absorption with 7, 14, and 19 tubes is achieved in 985, 404, and 317 s with an overall reactor weight of 78.46, 88, and 88.2 kg, respectively. The 14-tube reactor performance is investigated by introducing the longitudinal fins inside the tubes. The reactor performance is enhanced by allocating fins into different pairs of half and full fins constrained by overall fin volume. A thermal resistance network model is presented to investigate the effect of fin distribution and coolant velocity on equivalent resistance of the metal hydride reactor. Storage performance obtained from numerical model validates the thermal resistance analysis from heat transfer viewpoint. With six full fins, 90% hydrogen absorption is achieved in 76 s. However, tubes with 6, 8, and 12 pairs of half and full fins require 74, 58, and 54 s, respectively. The 14-tube reactor with 8 pairs of half and full fins is used for quantifying the augmentation in the absorption performance in response to operating conditions (supply pressure and heat transfer fluid temperature). A design methodology is outlined for the development of a large-scale multi-tubular hydride reactor based on a heat transfer optimization strategy.