Effect of Thermal Conductivity Enhancement of Thermochemical Energy Storage Material on Unused Heat Utilization System
Effect of thermal conductivity enhancement of thermochemical heat storage materials on thermal performance of heat storage system which can store unused heat at medium-temperature at up to 400oC was discussed experimentally and numerically. Magnesium oxide/water/magnesium hydroxide (MgO/H2O/Mg(OH)2) /solid reaction system had a potential to be used for thermochemical heat storage for the unused heat. However, the thermal conductivity of the material limited thermal performance of the heat storage system. Expanded graphite (EG) had a high thermal conductivity and high surface area, and was chemically inert. Composite material mixed with magnesium hydroxide (Mg(OH)2) and EG, which was named as EM, was developed for enhancement of thermal conductivity of the Mg(OH)2 material. The composite was formed into a tablet of 10 mm diameter and 7 mm thickness in experiment. Thermal performance of EM tablet bed was demonstrated experimentally by a packed bed reactor. Thermal performance of pure Mg(OH)2 pellet having 2 mm diameter and 5~10 mm length was compared with one of EM under the same reactor. The packed bed reactors’ behavior in dehydration operation corresponding with thermochemical energy storage was analyzed numerically. It was shown that enhancements of effective thermal conductivity of the EM pellet bed contributed on thermal performance enhancement of the packed bed reactor.