Sliding flow method for exergetically efficient packed bed thermal storage

The feasibility of a thermal energy storage method is highly dependent on its exergetic efficiency. The two major components which cause exergy destruction in packed bed thermal energy storage methods are pressure drop and temperature dispersion. It is difficult to prevent exergy destruction with existing packed bed type thermal storage systems because the effect of most physical parameters on the pressure drop is opposite to that on the mixing or axial dispersion. We propose a new sliding flow strategy in which fluid inlet and outlet ports change as the temperature front in the bed moves. In this design the typical distance between two simultaneously active inlet and outlet ports will be approximately equal to twice the axial dispersion length. The computations presented in this paper show that the sliding flow method (SFM) is expected to perform significantly better than existing methods and will result in substantial reduction in exergy destruction. The major advantage of the SFM is its ability to decouple thermal behavior and pressure drop effects, thus reducing the design constraints.