Conjugate Heat and Mass Transfer in Activated‐Carbon Hydrogen Storage Reactors With Liquid and Gaseous Heat‐Transfer Fluids: A Numerical Study

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ABSTRACT Hydrogen adsorption in activated‐carbon beds is a promising option for near‐ambient hydrogen storage, but its performance is strongly limited by heat release during charging and heat demand during discharging. This study numerically analyzes hydrogen adsorption and desorption in a vertical steel vessel packed with activated carbon and surrounded by an external heat transfer fluid (HTF) jacket. A transient conjugate numerical model is developed to solve the coupled mass, momentum, and energy balances in the porous bed, steel wall, and HTF domains. Hydrogen adsorption is described using the Dubinin–Astakhov isotherm and linear driving force kinetics. Four HTFs, namely water, thermal oil, air, and helium, are examined during adsorption under identical reactor geometry and imposed inlet conditions, while nitrogen is used instead of water during desorption to avoid possible freezing under low‐temperature operation. This replacement is treated as a practical operating choice rather than as an assumption of equivalence between water and nitrogen. The results show that HTF selection strongly affects hot‐spot formation, cooling and heating rates, wall heat flux, and usable storage capacity. At t = 400 s, water gives the lowest peak bed temperature, 376.5 K, and the highest hydrogen uptake, 22.5 mmol g −1 , whereas air gives the lowest uptake, 19.0 mmol g −1 , and air and helium produce higher peak temperatures of about 395–397 K. Compared with the air‐cooled baseline, water increases the usable hydrogen uptake by 18.4%, while oil provides a 10.5% improvement. During desorption at t = 4400 s, oil supplies heat more effectively from the jacket to the bed, whereas gaseous HTFs promote stronger cold‐core formation because of their limited sensible heat capacity. In general, liquid HTFs provide stronger thermal management than gaseous HTFs, reducing adsorption hot spots and improving hydrogen uptake. The findings provide quantitative guidance for HTF selection and external jacket design in activated‐carbon hydrogen storage reactors operating near ambient conditions.

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