Theoretical models for the effective thermal conductivity of metal hydride bed under multiple heat conduction mechanisms

Accurate prediction of the metal hydride (MH) bed’s effective thermal conductivity (ETC) is key for precise MH reactor design. Existing ETC models often do not fully account for multiple heat transfer pathways and neglect the dynamic variations in gas thermal conductivity and interparticle contact state, resulting in large deviations between predicted hydrogen absorption and desorption rates and experiments. This study develops two ETC prediction models for MH beds, both established by simultaneously considering three heat transfer pathways and the Smoluchowski effect in the pore space, which apply to non-hydrogen conditions without reaction (TCI model) and to hydrogen conditions with reactions (TCI-HAD model), respectively. The TCI model accounts for gas thermal conductivity changes and multiple heat transfer paths, with a validation deviation of 2–8 % under both atmospheric and dynamic gas pressure. Compared with other ETC models that do not couple reactions, the TCI model exhibits the best comprehensive prediction accuracy and strong applicability. Then, based on the TCI model, the TCI-HAD model for the hydrogen atmosphere is constructed by further considering the change of the interparticle contact state with the reaction fraction. Experimental verification results show that the mean absolute percentage error (MAPE) of the TCI-HAD model is 6.15 %. Compared with other ETC models that couple reactions, the TCI-HAD model achieves the highest prediction accuracy, with MAPEs of 4–10 %. Finally, based on the TCI-HAD model, the effects of particle size, MH bed temperature, and MH bed porosity on ETC were investigated during the hydrogen absorption process, respectively. Results indicate that the MH bed temperature and porosity are the main factors affecting ETC. The ETC models proposed in this study can provide theoretical support for investigations of coupled heat and mass transfer in MH beds, as well as for the determination of ETC in numerical simulations of MH reactors.