HEAT TRAP AND STORAGE PERFORMANCE OF SALT HYDRATE PACKED SOLAR AIR HEATER

A solar air heater packed with a salt hydrate was developed to improve the performance of both heat trap and storage. Using calcium chloride hexahydrate as the salt hydrate, a glass tube bundle packed with the salt was set in the collector. The air heater was exposed to radiant heating by infrared lamps. The heat trap and the storage characteristics of the air heater were examined by measuring the transient temperature distribution of salt and air in the collector. When the lamps were turned off after attainment of a steady-state heating condition, outlet air of stable temperature around at the melting point was obtained for a time longer than 5 hours, and a much greater effect of latent heat storage was observed in comparison with that of an air heater with glass tube bundle but without the salt. A suspension of fine graphite particles in the salt enhances the heat trap efficiency due to the change in its optical properties. The suspension not only increases the molten part of the salt close to the collector inlet but also improves the crystallization due to its function as a nucleus. The heat storage capacity increased as a result. Good performance of this type of solar air heater was also found in an outdoor experiment.