Experimental and theoretical study of total and radiative heat transfer incirculating fluidized beds

A new heat transfer model is proposed for suspension-to-wall heat transfer in circulating fluidized beds. The model assumes an emulsion layer with var ying temperature and solids concentration close to the heat transfer surfac e and a thin gas layer between this layer and the wall. The packet model of Mickley and Fairbanks (1955) is used to predict convective heat transfer t hrough the emulsion layer, while conductive heat transfer through the gas l ayer is estimated based on its thickness. Independent scattering theory is employed for radiative heat transfer in the non-gray, absorbing, emitting a nd anisotropically scattering emulsion layer. The discrete-ordinate method is used to solve the radiative heat transfer equation. The predicted total and radiative heat transfer coefficients are compared with new experimental results obtained in a 152 mm x 152 mm s x 7.3 m tall CFB combustion pilot unit using a multifunctional probe and silica particles of mean diameter 28 6 and 334 mu m at temperatures from about 800 to 900 degrees C. The model g enerally gives good predictions of these experimental results, as well as o thers from the literature. (C) 1999 Elsevier Science Ltd. All rights reserv ed.