Transient response of a packed bed energy store employing a convecting gas vapour mixture

Low temperature transient operation of a packed bed thermal energy store, employing a convecting gas/vapour mixture to enhance the effective conductivity of the store, is described. Comparisons are made between the transient response of the store and predictions from a computer model which treats heat transfer through the store as a transient, one-dimensional conduction problem. Effective conductivities for the conduction model are obtained from previously measured steady state Nusselt number versus Rayleigh number data for the system. The comparisons show that (a) the simple one-dimensional transient conduction model, useful for system simulation, gives an adequate representation of store behaviour, and (b) the conductivities measured at steady state can be used in the transient model, implying that the high values achieved with gas/vapour mixtures at steady state, apply during transient operation. Further work to develop the storage system, and to improve understanding of the complex processes within it, is described.