Pressurised-cell test stand with oscillating heating for investigation heat transfer phenomena in metal hydride beds

Abstract

In this paper we present the apparatus and methodology for investigating the thermal diffusivity (TD) of metal hydride (MH) beds when exposed to a range of temperatures and pressures. For this purpose a pressurised-cell test stand has been designed, manufactured and assembled. The system is based on a cylindrical pressure vessel, with Peltier elements on both bases of the cylinder, to provide symmetrical heat delivery along the axis. The pressure cell design allows both thermophysical property measurements and studies of heat transfer phenomena accompanying hydrogen absorption and desorption in metal hydrides. The effective TD is measured using a modified Ångström method, i.e. a modified temperature oscillation method. The first of introduced modifications accounts for a finite longitudinal specimen dimension. The second alteration enables the measurements to be performed in temperature scanning mode. TD can be calculated both from the amplitude and from the phase change of the temperature response signal.The system and the developed methodology have been tested by measuring the effective thermal conductivity of the powdered LaNi5 bed. Investigations have been performed under inert gas, with pressure ranging from medium vacuum conditions up to about 0.45 MPa of nitrogen and helium. In the paper we present obtained results and compare them against the results from similar investigations performed in open cell apparatus under atmospheric gas conditions. Both the very good accuracy and the effectiveness of the developed procedure was demonstrated.