Heat transfer and fluidization characteristics of a high-temperature shallow fluidized bed

Experiments were carried out on the heat transfer and fluidization characteristics of a very shallow fluidized bed at high temperatures. Argon, helium, and air were used as working gases, and zirconia beads and silicon carbide particles were used as solid particles. In the experiment at a medium temperature range (bed temperature T_b ≤ 680 K), heat transfer characteristics with various particle materials and gases correlated well with the dimensionless variables calculated from 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; finally, fluidization stopped completely. In some cases the fluidization recovered when the gas temperature was decreased. This phenomenon may be attributed to the impurities from thermal insulation material. It should be noted that the impurity content in working gas, even though only a small fraction, is very detrimental to the fluidization and heat transfer characteristics of a very shallow fluidized bed operated at a high temperature.