Latent heat thermal energy storage in salt hydrates and clathrate hydrates

Thermal energy storage in the temperature range useful for residential water and space heating can be accomplished in the latent heat of phase change of suitable storage materials. The selection and implementation of these materials is investigated. Three storage materials suitable for the 45-60;The acceptance of phase change storage is presently hindered by ineffective methods of heat recovery. Heat exchange via a vaporizing heat transfer fluid in direct contact with the crystallizing storage material is shown to alleviate problems associated with conventional heat exchangers. The criteria for choosing heat transfer fluids include their physical and chemical stability, alone and in conjunction with, the chosen storage materials. Tests show that fluorocarbons meet these criteria.;A comparatively high solubility of certain heat transfer fluids in selected storage materials was observed. The beneficial effect of this solubility on direct contact vaporization heat exchange is discussed. Long-term cycling experiments were performed on the effects of pH, the phase stability of storage materials, and the corrosion resistance of construction materials to the system components.;Latent heat storage at space cooling temperatures is presently limited to water ice. The use of clathrate hydrates for cold storage is proposed. Two problems encountered in developing clathrate cold storage are studied; the nucleation of clathrate and the clathrate formation rate. Suggested solutions include seed-induced nucleation and surfactant-enhanced formation rates. The dissociation temperature and pressure of the clathrate determine the operating conditions of the storage system. Controlling the composition of the clathrate by selectively filling the clathrate water lattice would allow the design of clathrate storage systems for arbitrary operating conditions.;Bench scale and prototype units were built to test direct contact vaporization heat exchange in both heat and cold storage systems. The bench scale device was used as a demonstration model while the prototypes are currently undergoing field testing. A foundation for a mathematical model of the operation of these devices is presented.