Transient thermal performance of an experimental packed bed thermal energy storage system

The transient thermal performance of an experimental packed bed thermal energy storage system, (TES), installed in the two-phase flow laboratory of the Mechanical and Aerospace Engineering Department of the University of Tennessee at Knoxville, was determined. In this study the working fluids used were refrigerants-12 and -113. Two types of packings were used; single solid phase 5/8" diameter glass spheres, and 1/2" diameter 5/16" thick encapsulated pellets of phase-change material. The phase-change thermal energy storage materials tested were of two types: PWC-73, which is a eutectic mixture of Glauber's salt that has a specified phase-change temperature in the range of 71-75 °F, and PWC-89 which is Glauber's salt and has a specified phase-change temperature of 89 °F. Both single-and two-phase working fluid results are presented.

The storage unit used consists of a randomly packed 5" diameter 4' long tube. In the case of single-phase working fluid runs with glass packing, an energy balance was carried out and was found to agree with theoretical calculations to within 10 percent. The measured heat-transfer coefficient for single-phase liquid working fluid runs showed good agreement with published literature on gas-solid packed bed systems. Single-phase working fluid data were obtained for a working fluid Prandtl number in the range of 6 to 8, and a modified Reynolds number in the range of 30 to 1200. Two-phase working fluid data were obtained for a bed inlet quality ranging from 0.3 to 0.9 at a refrigerant mass velocity of 23.5 pounds mass per minute per square foot.