Heat transfer by liquid convection in particulate fluidized beds

In this work the theoretical model for heat transfer from a wall to a liquid-solid fluidized bed by liquid convective mechanism has been proposed and developed. The model is based on thickness of boundary layer and film theory. The key parameter in the model is the distance between two adjacent particles which collide with the wall. According to the proposed model, the liquid convective heat transfer in a fluidized bed is 4 to 5 times more intense than in a single-phase flow. Additionally, the wall-to-bed heat transfer coefficient has been measured experimentally in water???glass particles fluidized bed, for different particle sizes. Comparison of the model prediction with experimental data has shown that size of the particles strongly influences the mechanism of heat transfer. For fine particles of 0.8 mm in diameter, the liquid convective heat transfer model represents adequately the experimental data, indicating that particle convective mechanism is negligible. For coarse particles of 1.5???2 mm in diameter, the liquid convective heat transfer mechanism accounts for 60 % of the overall heat transfer coefficient.