Transient heat transfer analysis of low-temperature packed-bed for Cryogenic Energy Storage system

The roundtrip-efficiency of a typical Cryogenic Energy Storage system can be increased from the existing 50-55% to as high as 85% and higher by using appropriate storage of heat of compression and low-temperature refrigeration. There are few options for storing low-temperature refrigeration at around 80 K and higher. One of them is to store this refrigeration using pebbles of granite or similar materials in a packed-bed. Similar systems have been studied earlier; however, few studies have investigated the heat transfer inside the bed for optimisation. In this work, we have attempted to develop an appropriate model to capture the heat transfer in that porous medium. The model has been adapted from the literature, modified to include variations in thermo-physical properties at such low temperatures, and converted from a one-dimensional model to a polar coordinate system to capture radial heat transfer along the bed. The model was validated using experimental data.