Cryogenic adsorption hydrogen storage with enhanced heat distribution – An in-depth investigation

• Experimental validated model for heat transfer in nano-porous material filled heat distribution structure is presented.
• Heat distribution structure properties show significant storage working condition dependency.
• New storage model with heat distribution structure was successfully validated at cryogenic conditions.
• Increased charging and discharging dynamics compensates for structure volume and mass penalties.

A numerical model for a cryogenic adsorption hydrogen storage with enhanced heat distribution structure is presented and validated by experiments. The investigations cover charging, discharging and dormancy at cryogenic conditions. Metal foam was implemented as heat distribution enhancement structure. The prediction of the effective thermal conductivity, keff_foam, over the entire storage working range was carried out using an experimentally validated unit cell approach. An increase of keff_foam by +33% was observed by lowering the temperature from 295 K to 77 K, given keff_foam = 4.87 W/(m·K). The novel 2D axis-symmetric storage model developed applies two energy equations, one for the storage bed and one for the foam. Further, important thermal effects such as hydrogen isomer conversion were considered in the model. The storage model predictions were within the measurement uncertainties. A 95% storage filling was measured after 300 s charging. The enhanced heat transfer in the storage allowed highly transient charging. The volumetric and gravimetric storage capacity increased after 300 s charging by 21.5% and 9.3%, respectively. This behavior compensated for the volume and mass penalties for the implemented foam structure. However, further storage material improvements and a storage optimized heat distribution structure, including cooling fluid piping, are foreseen to meet overall storage requirements.