Novel Segmental Model for Predicting Bed-to-Tube Heat Transfer Coefficient in Gas-Solid Fluidized Beds

Accurate prediction of the bed-to-tube heat transfer coefficient (HTC) is the foundation of developing efficient fluidized bed heat exchangers, but there is still a lack of an effective prediction method. In this paper, the heat transfer mechanism around the immersed tube is revealed through the correlation analysis method. A computational fluid dynamics simulation was conducted to provide various flow field data for a gas-solid fluidized bed with an immersed tube. A correlation analysis was conducted to characterize the relationship between the local HTC and various factors. The results show that Kendall’s rank correlation coefficient (r_k) between the solid phase volume fraction and HTC is less than 0.5 on the top of the tube, while the r_k on the bottom side exceeds 0.9. According to the distribution characteristics of r_k and the emulsion phase contacting time fraction (δ_e) around the tube, a theoretical model containing three different heat transfer mechanisms was developed. The threshold value for defining the dynamically changing boundaries of each heat transfer mechanism is obtained (δ_e = 0.88 and r_k = 0.82). A comparison analysis demonstrates that the proposed model can predict the average HTC with a deviation of less than ±25% within a wide range of particle sizes (100-1000 μm).