Modeling of heat transfer between a high-temperature fluidized bed and an immersed surface by a surface-particle-emulsion model

The heat transfer between a high-temperature fluidized bed with magnesite and hollow-corundum sphere particles of diameter 0.35–1.21 mm as bed materials and an immersed surface is simulated using the surface-particle-emulsion heat transfer model developed by the authors. Considering the variance of the voidage in the emulsion in the vicinity of an immersed surface, heat transfer near the surface is treated as that through dispersed particles touching the surface and through the homogeneous emulsion when the distance from the surface is larger than one particle diameter. The predictions for the time-averaged overall heat transfer coefficients of the model agree well with the experimental data. The calculations show significant inhomogeneity in the temperature profiles and in the thermal properties within one particle diameter near an immersed surface. With increasing the surface temperature, the instantaneous heat transfer coefficient increases rapidly. The effects of particle diameter, bulk density and U/UmfU/Umf on the time-averaged overall heat transfer coefficient and its conductive, convective and radiative components are also computed and discussed. For hollow-corundum-sphere particles with diameter 0.87–1.21 mm and bulk density 386–870kg/m3, the time-averaged conductive heat transfer coefficient has a share of 57–43%, radiative 37–51, convective 5–3% for 950∘C bed temperature and U/UmfU/Umf from 1.1 to 4.0.