A comparison of radial-flow and axial-flow packed beds for thermal energy storage

Packed-bed thermal reservoirs are an integral component in a number of electrical energy storage technologies. The present paper concentrates on packed beds where the heat transfer fluid travels along the radial co-ordinate. The governing energy equations and various mechanisms that cause exergetic losses are discussed. The radial-flow packed bed is compared to a dimensionally similar axial-flow packed bed. This approach provides a fair assessment of the underlying behaviour of the two designs. Multi-objective optimisation allows a wide range of design variables to be considered, and is employed to compare optimal radial-flow and axial-flow stores. Axial-flow stores that have been segmented into layers are also considered. The results indicate that radial-flow stores have a comparable thermodynamic performance, but that the additional volume required for by-pass flows leads to higher capital costs.