Thermal Property Measurements of High Pressure Metal Hydrides
Metal hydrides are potential materials for onboard hydrogen storage. Thermal property measurements are needed to optimize the thermal management design of metal hydride storage systems which require a measurement technique developed with considerations of the thermodynamics of the hydriding process and the pyrophoric nature of the material. In the present work, a transient plane source (TPS) apparatus was integrated with a pressure vessel to measure effective thermal conductivity (keff) and thermal diffusivity (α) of metal hydrides in a high pressure hydrogen environment (up to 275 bar) for the first time. From these direct measurements, the material specific heat (CP) was derived from isotropic property relations. Furthermore, a custom pellet press was fabricated to make metal hydride pellets, including additives for structural integrity and thermal enhancement.
Thermal properties of Ti1.1CrMn in oxidized pellet, oxidized powder, activated powder were measured. Pellets composed with graphite and polyvinylidene fluoride (PVDF) had the highest keff between 6.3 and 6.9 W/m·K. Pellets with aluminum powder had a keff of 1.7 to 3.5 W/m·K, dependent on the compression force applied on the pellets. Oxidized powder keff increased from 0.80 to 1.6 W/m·K with increasing hydrogen pressure from 0.17 to 275 bar. The pressure dependence of keff was attributed to the change in mean free path of the hydrogen gas with pressure. In contrast to oxidized powder, keff of activated Ti1.1CrMn powder ranged from 0.31 to 0.71 W/m·K as a function of hydrogen xiv pressure from 2.9 to 253 bar. While keff was only dependent on the hydrogen pressure, both α and CP data of activated powder had strong dependencies on the hydriding reaction progress. This dependency was attributed to the change in metal hydride lattice structure between the desorbed and the absorbed phase, which affected the phonon transport. The present thermal property study provided data and insights for the implementation of efficient thermal management in metal hydride based onboard hydrogen storage systems.
Researchers should cite this work as follows:
- S. Flueckiger, Thermal property measurements of high pressure metal hydrides, MS thesis, Purdue University, West Lafayette, IN, 2009.