Investigation on energy and mass distribution characteristics of granules in the composite heat exchanger

A composite heat exchanger for high-temperature granule waste heat recovery is proposed. Granular mass and energy distribution within the composite heat exchanger are simulated via the CFD-DEM coupling method. The effects of granular size, cooling gas velocity, and granular mass flow rate on granular distribution and the temperature distribution are analyzed. Results demonstrated that under the combined action of airflow impact force and gravity, the granule produces an uneven distribution in time and space. Larger granule tends to be positioned closer to the gas inlet horizontally. Along the direction from the gas inlet to the gas outlet, granules exhibit a trend of decreasing size, mass, and temperature. The influence of gas velocity predominantly affects the area coverage rate, whereas the effect of granular mass flow rate is minimal. The area coverage rate initially increases with rising gas velocity and subsequently decreases, peaking at 73.8 % at 12 m/s. After the heat exchange process reached a stable state, the number of contacting granules accounted for only 0.37 % of the total granules, making heat conduction between granules negligible. Convective heat transfer dominates, accounting for approximately 86.52 % of the total heat exchange, while radiation heat transfer accounts for about 13.48 %.