Metal hydride, Thermal conductivity, Hydrogen energy, Heat exchanger, Heat transfer accelerator
The expectation for renewable energy is rising from the viewpoints of recent environmental problems and energy problems. The reason why renewable energy is not widespread is that there are temporal and spatial restrictions on real application. There is an increasing interest in hydrogen energy as energy that compensates for such weaknesses of renewable energy. Hydrogen can easily converted to be thermal energy, mechanical energy, electric energy and used. It is important to establish effective saving techniques for effective development of hydrogen energy systems. Three methods of liquification, pressurization and metal hydride (on briefly, referred to as MH) are the major hydrogen energy storage methods. In this study, we focus on the hydrogen storage by using the metal hydride. MH can storage hydrogen with high density, and it can be used at low temperature and low pressure, but has the disadvantage that the release rate of hydrogen due to the low effective thermal conductivity of the MH alloy layer. In this study, the heat transfer enhancement effects of several fins on metal hydride particle layer are estimated by experiment and simulation. The unsteady state heat conduction calculation of MH alloy layer with and without fins was conducted with the Solidworks simulation soft and, the experimental and the calculation parameters are charging volume ratio of fins, and the shapes of fin like as cross fin and circular cross fin. Another estimation parameter is the diameter of storage tank. One storage tankhas an outer diameter of 80 mm, an inner diameter of 78 mm, the other has an outer diameter of 25 mm and an inner diameter of 23.5 mm. The number of fins was increased until the charging volume ratio of the fin, 25 volume %, we estimated the heat transfer enhancement influence of the fins on the MH ally layer. According to our calculation results, the effective thermal conductivity is increased with increasing of charging volume ratio of fin, but this heat transfer enhancing effect is saturated at over 10 volume % of it. In oursimulation model of a circle cross fin, the tank which have an outer diameter of 52 mm and an inner diameter of 50 mmwas used. In the simulation results of using circle cross fins cases, the highest heat transfer enhancement effect was obtained when circular diameter of circular cross fin was 24 mm. Compared with cross fins (which has a heat transfer enhancing effect of 4.68 times compared with without fins), the volume content of circular cross fin was 1.4% higher than that of cross fin. However, the heat transfer enhancement effect of circular cross fin was 2.46 times higher than that of cross fin. And, it is confirmed that circle cross fin which have charging volume ratio, under 10% can achieve a high heat transfer enhancing effect and is suitable to heat transfer enhancing of MH particle layer.