Influence of air distributors on heat transfer and hydrodynamic performance in fluidized bed heat exchangers

This study experimentally investigated the influence of distributor geometry including perforated plates with different open-area ratios (OAR = 21.6%, 6.36%, and 3.97%) and a bubble-cap distributor (OAR = 6.36%) on the thermal hydrodynamic performance of a fluidized bed heat pipe heat exchanger. Experiments were conducted using silica sand particles with mean diameters of 176.7 ?m, 353.5 ?m, and 707.7 ?m under hot-bed and cold-bed conditions, where bed-to-surface heat transfer coefficients, distributor and bed pressure drops, and blower power consumption were systematically measured. The bubble-cap distributor consistently enhanced the heat transfer coefficient, yielding 15%-30% higher values than perforated plates. Increasing particle size reduced heat transfer by ~20% due to reduced surface area and particle-wall contact. Distributor pressure drop, Pd, increases sharply with decreasing OAR from 400 at 21.6% to 1700 Nm-2 at 6.36%, while overall bed pressure drop, Pb, reaches 3200 Nm-2 for OAR 3.97%, compared with 1200 Nm-2 for 21.6%. An obvious trade-off is observed: bubble cap shows the highest heat transfer h ? 250 W/mK but consumes almost double blower power 120 W than 60 W required high-OAR perforated plates with h ? 180 W/mK. These results validate that bubble-cap distributors maximize thermal efficiency, while perforated plates with higher OAR are more beneficial for operation. They are in agreement with the general tendency reported in prior work Byregowda 2023, Yudin 2020 but provide a comprehensive analysis of the evaluation of heat transfer, hydrodynamics, and power consumption and thus provide practical directions to industrial applications of waste heat recovery systems.