Enhancement of Heat Transfer in Hydrogen Storage Tank Using Hydrogen Absorbing Alloy (Improvement of Metal Hydride Tank Design for High Charging Rate)

A hydrogen storage system using metal hydride (MH) has several problems to be solved before practical use. Among of them a long charging time required due to the poor heat transmission in MH bed during exoergic hydride forming reaction is essential for the hydrogen storage system of fuel cell electric vehicles. Four small tanks (effective hydrogen capacity 1.25 Nm3) using a La-Ni based AB 5 type hydrogen storage alloy were made by way of trial to attain the charging time within 10 minutes absorbing 80% of effective hydrogen capacity. The experiments were carried out to evaluate effects of thermal design of the tank, coolant condition on hydrogen absorption rate. Calculation of the process was done to improve performance of heat transfer in MH bed with additional thermal fins and rearrangement of coolant channels. The final version of the tank satisfied the required charging time even for higher coolant temperature of 21 deg C which reduces chiller load of a hydrogen station.