A model to determine the overall bed-to-wall heat transfer coefficient and its influence factor analysis in moving bed

摘要

Waste heat recovery of hot particles based on the moving bed is recognized widely in the industrial applications. However, the heat transfer process in the moving bed is complicated and there is still a lack of effective heat transfer model to predict accurately the heat transfer behavior of moving bed. In this paper, a heat transfer model is developed to calculate the overall bed-to-wall heat transfer coefficient of moving bed containing randomly packed mono-sized spherical particles. In this model, the radiation and the conduction are the main modes of heat transfer. Due to the downward movement of particles in the moving bed, the convection between the particles and the gas is indispensable for this model (only convection caused by particle movement is considered in this paper). And the convection is incorporated in the particle internal conduction as boundary condition. By comparing with the experimental data, it is verified that this model can predict effectively the overall bed-to-wall heat transfer coefficient of moving bed under various working conditions. The effects of parameters such as the particle temperature, the particle size and the particle descending speed on the heat transfer coefficient are also taken into account. Especially, the particle descending speed has a crucial influence on the heat transfer behavior of moving bed, which has been studied rarely in previous researches. The results show that the increase of particle descending speed has a positive effect on the heat transfer of moving bed, which contributes to the industrial design of waste heat recovery of hot particles.