Large eddy simulations of turbulent heat transfer in packed bed energy storage systems

Abstract

The present paper aims to study the effect of partial blocking and flow regime on the mutual turbulent interplay between porous and non-porous regions in packed bed energy storage systems (PBESSs). To this end, high-fidelity pore-scale large eddy simulations (LES) are conducted for two PBESS configurations, namely full blockage and partial blockage under the discharge process at three Re numbers 3600, 7200, and 14,400. The influences of the flow major features, including flow channelling and leakage, on the rate of heat transfer (Nusselt number) and pressure drop are investigated for various flow Reynolds (Re) numbers. Results demonstrate that the channelling effect inside the porous region strongly affects the temperature profiles and leads to local maximum peaks of Nusselt (Nu) number on the upper and lower sides of pore elements. For the partial blockage, it is observed that 79 % of the flow entering the porous block leaks from the porous region into the non-porous region through the porous-fluid interface at Re = 3600, which reduces by 26 % as the Re increases to 14,400. The flow leakage leads to the formation of counter-rotating vortex pair structures inside and over the porous block. It also causes local maximum peaks of Nu number at the lower sides of pore elements and changes the stagnation points' position at the leading edge of the porous block near the porous-fluid interface. Compared to the full blockage configuration, temperature profiles inside the porous block are less dependent on the Re number for the partial blockage case. Finally, the pressure drag force for the full blockage is about 21.4 and 30.9 times that of partial blockage at Re = 3600 and 14,400, respectively. Whereas at these Re numbers, the average Nu number for the full blockage is nearly 51.2 % and 57.3 % higher than that of the partial blockage. Consequently, blocking the entire fluid flow area may not necessarily be the best design, since it may result in excessive pressure drops without significant heat transfer enhancement.