On-board vehicle hydrogen storage poses a challenging engineering task to fulfill relevant design and operational criteria. Until now mostly data on small material probes have been published.
Coordination polymers or metal organic frameworks (MOF) have been identified as a promising adsorption type storage materials with gravimetric storage densities of up to 7.5 wt% at 77K and specific surfaces of 4,400 cm²/g.
An advanced tool for the numerical simulation of real tank systems has recently been developed. The mathematical model describes heat transfer, fluid flow and the sorption process in a cylindrical adsorption type hydrogen storage tank. The model is solved using the spectral element method combined with an overall third order accurate time stepping scheme. Numerical experiments show that the time to fill the tank decreases with increasing charging pressure and that low conductive heat fluxes constrain the filling process.
In parallel, experimental investigations of thermal effects in a dynamic hydrogen cryo-adsorption storage system have been undertaken to validate the numerical model. The chosen adsorbent is commercially available granular activated carbon to calibrate the experimental setup before more advanced materials are being tested. Operating conditions were compatible with practical applications for hydrogen on-board storage systems. The temperature and pressure changes in the cylindrical storage tank during both filling and discharging of the tank were measured.
The next step is to develop tailor-made coordination polymers in bulk, characterise them and examine their operational properties in real tank systems with relevant heat exchanger designs under varying design and operational conditions.