Numerical investigations on the absorption of a metal hydride hydrogen storage tank based on various thermal management strategies

This study presents numerical investigations on the performance of the charging process of a metal hydride-based hydrogen storage tank. Three scenarios were developed to examine the absorption performance and compare the effectivenesses of proposed thermal management alternatives. In Scenario-1, the metal hydride (MH) tank is cooled with convective heat transfer on the lateral surface of the tank, i.e., external convection. In Scenario-2, phase change material (PCM) is wrapped around the MH tank to investigate passive thermal management. Scenario-3, a hybrid approach, includes the PCM layer and an internal cooling pipe. In this scenario, the heat transfer fluid (HTF) inside the tube is activated depending on the temperature within the MH tank. An in-house 2D axisymmetric numerical code was developed using the finite volume approach in MATLAB software. In the parametric study, several design parameters and operating conditions were selected, such as (i) charging pressure, (ii) external convective heat transfer coefficient, (iii) PCM thickness, (iv) latent heat of PCM, (v) HTF temperature, and (vi) convective heat transfer coefficient of the HTF, and as a total of 334 parametric analyses were conducted by varying the numerical values of the parameters chosen in wide ranges. The outputs, like spatial and temporal variations of hydride bed temperature and weight fraction, are evaluated for each of the proposed scenarios. As a result, it was observed that the storage performance strongly depends on the convection coefficient at ambient conditions. In Scenario-1, beyond 1000 W/m2K, convective heat transfer coefficient variations do not cause a significant change in the charging process. In Scenario-2, variations in PCM thickness do not cause a considerable change in the storage performance significantly beyond 3 cm. The variations in PCM thickness become important at lower latent heat values and PCM thicknesses less than 2.5 cm. In Scenario-2 and Scenario-3, PCM thickness over 2.5 cm and latent heat of fusion parameter over 150 kJ/kg should be selected to provide a thermal management strategy to be implemented. While the storage criteria were determined according to different thermal management strategies, the PCM thickness and latent heat of fusion parameters showed higher storage performance than the external convection coefficient at the same charging pressure. Temperatures at critical nodes in the MH-PCM system vary depending on location and reaction time. For all thermal management strategies in the hydride bed in positional temperature distributions, the temperature is minimum at the nodes close to the straight pipe. In the scenario-based analysis of the hydride bed temperature, the Scenario-3 thermal management strategy provides the MH bed domain at a lower temperature than Scenario-2. Here, the convection coefficient inside the cooling channel is a critical parameter for the hydride bed temperature