Heat Transfer from High Temperature Gases in a Very Shallow Fluidized Bed

Experiments were carried out on heat transfer and fluidization characteristics of a very shallow fluidized bed at high-temperatures. Argon, helium, and air were used for working gases, and zirconia beads and silicon carbide particles were used for solid particles. In the experiment of a medium-temperature range (bed temperature T_b<680 K), heat transfer characteristics with various particle materials and gases were well correlated with the dimensionless variables calculated with the thermophysical properties at the temperature of gas jets from a multislit distributor. These dimensionless data showed good agreement with Andeen and Glicksman's empirical formula. As the operating temperature was increased (T_b>680 K), the fluidization deteriorated; then, the heat transfer coefficient decreased very rapidly; and finally, fluidization stopped completely. In some cases, the fluidization recovered again when the gas temperature was decreased. This phenomenon may be attributed to the impurities coming from insulation material. It should be noted that the impurity content in working gas, even though a small fraction, plays a very detrimental role in the fluidization and heat transfer characteristics of a shallow fluidized bed operated at a high temperature.