Molerus and Wirth's heat transfer model for bubbling fluidized beds: Proposal for an extended model including immersed tube banks and particle cross-flow

While there are many semi-empirical correlations for estimating the wall-to-bed heat transfer coefficient in a fluidized bed, most are only usable in a limited range of operating conditions. The correlation developed by Molerus and Wirth (1997) provides the most expansive and successful model; however, it does not consider the influence of the properties of an immersed tube bank or a horizontal movement of particles (cross-flow). This study expands Molerus and Wirth's correlation to include these additional influencing factors by identifying and introducing new dimensionless factors using dimensional analysis. Collected secondary data and measurements from a test rig were used to evaluate the extended model. The model's estimates largely align with the collected secondary data and previously published models describing the influence of tube diameter and tube packing density on the wall-to-bed heat transfer coefficient. The model also provides new insight into the conditions under which a particle cross-flow contributes significantly to the wall-to-bed heat transfer coefficient. Future research should use these findings to conduct targeted measurements and further improve the model's predictions.