Experimental study of thermal behavior during charging in a thermal energy storage packed bed using radial pipe injection

The thermal behavior of an air-alumina packed bed storage system is studied experimentally via heating the bed domain radially. A perforated tube is inserted at the center along the axial length of the bed domain to charge the bed radially. Air was used as heat transfer fluid (HTF) with inlet temperature of 75 degrees C and 6 mm alumina beads were used as solid storage materials. This paper analyzes the storage efficiency of several radial designs compared to the traditional axial method. First, the storage process is analyzed by charging the bed radially using several different radial tube designs (six designs based on hole sizes). These hole patterns are analyzed to obtain the best even flow and thermal distribution in the radial direction, focusing on storage energy and temperature profiles. A gradient in hole sizes is needed, with smaller holes toward the outlet. To ensure HTF flowed radially from the center to the packed bed walls, additional plates were inserted into the bed to force gas to the wall. These plates were solid except for four holes around the edge of the plate at r = R. The charging efficiency is analyzed based on the first law of thermodynamics. The results show that during charging the radial configuration stores more energy compared to the axial flow configuration. The charging efficiency increases from 75.3% (axial flow) to 80.3 +/- 2.8% (radial flow with two plates).