Heat transfer to horizontal tubes in fluidized beds: Experiment and theory

A theoretical model, applicable over a wide range of fluidizing conditions in bubbling and slugging beds, is proposed. The theory assumes that heat exchange between a cold fluidized bed and a horizontal tube takes place by three parallel paths-heat is transferred by packets of particles, by gas percolating between the particles and the tube surface, and by gas bubbles or slugs. Correlations are presented for the corresponding particle convective, gas convective, and bubble heat transfer coefficients, as well as for the voidage around the tube. An analysis shows that, from a heat transfer standpoint, particles may be classified as fine, intermediate, and large. For each of these cases, equations for the time-averaged heat transfer coefficient to the tube as a whole are given. The model is introduced for the conductive and convective modes of heat transfer.