Effects of exit-pressure variation on the hydrogen supply characteristics of metal hydride reactors

Here we examine how the temporal mean and steadiness of the hydrogen discharge rate of a metal hydride reactor (MHR) vary, when its exit-pressure is deceased quadratically with time. To accomplish this task, a mathematical model accounting for the hydrogen desorption kinetics of LaNi5 and the mass and energy balance in a cylindrical MHR is solved numerically. The initial and final exit-pressures of the MHR are prescribed, whereas the “pressure-drop time” (tPD, during which the exit-pressure is decreasing) and the initial exit-pressure drop rate ( p ˙ e 0 ) are the control parameters. Results of a systematic parameter study indicate that, for a given tPD, increasing p ˙ e 0 generally increases the mean hydrogen discharge rate, while there is a particular p ˙ e 0 that minimizes the variance of the hydrogen discharge rate. The MHR exit-pressure variation therefore can be “optimized” to discharge hydrogen with maximized temporal steadiness. Some other strategies for MHR performance improvement also are discussed here.