Investigation of heat transfer between a horizontal tube and gas–solid fluidized bed

Experiments have been carried out in a fluidized bed in order to verify the influence of the axial position, particle diameter and the superficial gas velocity on the heat transfer coefficient from a small horizontal tube (Dt = 8 mm) immersed in the fluidized bed. The solid particles used were 280, 490 and 750 μm diameter sand particles, fluidized by air. The experimental results showed that the heat transfer coefficient is increased with increasing the gas velocity, up to a maximum, and then decreases with a slight slope. The heat transfer coefficient was found to decrease by increasing the particle size. The probe position had less influence on the heat transfer coefficients. In order to predict the heat transfer coefficient from the fluidized bed to a horizontally immersed tube, a cluster based model has been proposed. The model predictions were compared with the experimental data of this work as well as those from the literature in a wide range of operating conditions. A close agreement was found between the model predictions and the experimental findings.