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 (delta(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 (delta(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 mu m).