Numerical modelling and optimization of packed-bed thermal-energy storage system

Abstract

In this work, numerical modelling (including convection and radiation heat transfer) of Packed-bed storage systems (PBSS) is carried out and the effect of various system parameters affecting the efficiency and temperature is studied. One dimensional forms of the time-dependent, coupled partial differential equations for energy conservation of the heat transfer fluid (HTF) and the packing materials are solved using the finite difference method to design a PBSS for a given mass flow rate for 0.125 MWh (0.45 GJ). The packed-bed material is assumed to be spherical with an average diameter, and the mass flow rate, void fraction, packed bed material diameter, heat transfer fluid (HTF), and the packed-bed materials are varied for optimal efficiency during charging (i.e. when the temperature of HTF is greater than that of the packed bed). The results are compared with the analytical solutions for validation. Present solutions (considering only convection) are found to be matching reasonably well with the analytical data. With the validated model, the radiation heat transfer effect on the packed-bed is modelled (along with the convection) and void fraction, mass flow rate of HTF, a diameter of the packed-bed material, different HTF, various packed-bed materials are compared for maximum efficiency. From the present work, a PBSS design with void fraction =0.45, mass flow rate =1.8 kg/s, the average diameter of the packed-bed material = 0.02 m, water as HTF, and brick as packed-bed material is found to give the maximum efficiency along the length of the packed-bed.