Studies on thermal energy storage system with ceramic honeycomb channels

Abstract

In this study, a ceramic-based sensible thermal energy storage system is analysed using analytical and numerical models, and the results subsequently validated with laboratory experiments. Corundum mullite monoliths are used as the storage material which is thermally cycled using compressed air as the heat transfer fluid (HTF). Here, hexagonal channels in the monolith allow direct contact heat exchange between the air and the storage material. The storage system is composed of a packed bed of ceramic blocks having honeycomb flow passages. However, unlike the case of packed bed of unconsolidated storage materials, the arrangement of these blocks plays a crucial role in the performance of the storage system. In this study, we try to bring out this crucial aspect of block arrangement and the effect it has on the flow characteristics and hence on the charging and discharging dynamics of the system. To understand the effect of ceramic block configuration in a storage system, two separate block arrangements are explored: parallel flow arrangement and series flow arrangement subjected to a single charging and discharging cycle. The storage systems are subjected to a constant temperature front of 450 K during charging cycle and 300 K during discharging cycle. Firstly, an analytical model is developed for airflow through a ceramic channel that predicts the temperature-time history of the storage system and the HTF at the system outlet. Subsequently, a full CFD analysis for coupled flow and conjugate heat transfer is performed on the two block arrangements, considering the actual three-dimensional ceramic block geometry with honeycomb channels. To validate the results of the analytical and numerical models, experimental testing is performed on a laboratory scale test setup. Finally, the effect of air velocity on the charging-discharging dynamics for the two arrangements of the ceramic blocks is also discussed. It is observed that the series flow arrangement charges and discharges the storage system 1.5 times faster than the parallel flow arrangement of the ceramic blocks but with four times higher pressure drop.