Characteristic features of heat and mass transfer in hydrogen energy storage systems

Abstract

Reversible metal hydrides are efficient solution for energy storage for distributed and autonomous power. Heat transfer is the major limiting factor for performance of metal hydride devices. Exothermic hydrogen absorption creates significant temperature gradients due to low effective thermal conductivity of powdered metal hydride beds. As the result of a strong dependence of absorption equilibrium pressure on temperature, this gradients lead to heat and mass transfer crisis and compositional inhomogeneities with high concentration of hydride phase near heat sinks and low concentration in the hot core of the bed. Development of the compositional inhomogeneities is accompanied by significant pressure drops over the bed, which can be measured experimentally. We performed experiments on hydrogen absorption in 1 kg metal hydride bed of of La0.9Ce0.1Ni5 inside a water cooled reactor during charge at constant hydrogen flow within the range of 10-30 st.L/min at 0.59 MPa. Results show that heat and mass transfer crisis starts, when pressure in the reactor near hydrogen inlet becomes close to supply pressure, while pressure on the other side of the bed is lower by 0.15-0.25 MPa. These results confirm development of the hot core inside the bed, where reaction almost stops due to high temperature.