Phase Change Cooling of a Metal Hydride Reactor for Rapid Hydrogen Absorption

As the world is keen on cleaner and sustainable energy, hydrogen energy has the potential to be part of the green energy transition to replace fossil fuels and mitigate climate change. However, hydrogen energy storage is a difficult task since physical storage in the form of compressed gas under high pressure is associated with safety issues. Another form of hydrogen storage is material-based storage, which is the safest way to store hydrogen energy in a particulate matter, known as metal hydrides. Metal hydrides can store hydrogen at room temperature and use less volume to store the same amount of hydrogen compared to classical gas tanks. The challenges with the metal hydrides reactor are their slow charging process and the requirement of proper thermal management during the charging process. In this study, a metal hydride reactor model is developed in COMSOL Multiphysics, and the associated heat transfer simulations are performed. The main objective of this research is to optimize the cooling channel design in the metal hydride reactor, where the R-134a coolant rejects heat through both latent and sensible heat transfer. The study showed that the phase-changing coolant and varying convection coefficient along the length of tubes significantly reduce the hydrogen charging time and the peak temperature of the reactor during hydrogen absorption. The pumping power analysis for the R-134a flow was also conducted. The computation results reveal that coolant channel configurations with nine or more tube-passes require significantly large pumping power.