Investigation of a low heat loss high temperature thermal energy storage system

A low heat loss thermal energy storage system capable of storage in a range of 250-100 F is described. The design criteria called for a storage system that is simple to construct, uses inexpensive and readily available materials, utilizes an insulating material with a thermal conductivity between 0.003 - 0.015 Btu/hrft F for temperatures ranging between 250-100 F, and be suitable for residential or commercial applications. A design selected to fulfill the above criteria consists of a double tank wherein the annular space between the tanks is filled with a porous powder (silica) and then evacuated to a pressure of approximately 1 mm Hg. Thermal conductivity values of 0.0029 - 0.1100 Btu/hrft F were achieved experimentally for vacuum levels ranging from 0.5 - 3.0 mm Hg and hot surface temperatures ranging from 340 - 711 F.