Solidification Behavior for Direct Contact between Sugar-alcohol Latent-heat Storage Materials and Heat Transfer Oil

The purpose of this study is developing a latent heat storage system that uses waste heat from factories in the temperature range 100–200ºC as a heat source. Mannitol and a mixture of mannitol and erythritol, which are sugar alcohols, were used as phase change materials (PCMs). We also studied a direct contact heat exchange method with lower thermal resistance.The solidification behavior was examined in detail using a test section consisting of a Pyrex glass tube with one nozzle hole for injecting heat transfer oil. The tube had an inner diameter of 87 mm and height of 300 mm. There was a nozzle plate with one hole that had a diameter of 2 mm in the lower part of the test section, and heat was transferred to the PCM by injecting heat transfer oil from the hole.The findings were the following. The heat transfer oil droplets from the hole start to solidify on the upper surface of the heat storage material. As time elapses, solidification starts near the nozzle plate. The oil droplet diameter increases with increasing flow rate. The diameter of the liquid column increases owing to solidification near the nozzle plate. The initial solidification shape of the mannitol–erythritol mixture (70% mannitol and 30% erythritol) is different from that of the mannitol. In addition, the observed solidification has a different shape depending on the flow rate.