Flow transition of solids in a three phase fluidized bed has been studied in a 15.2 ㎝-ID pyrex glass column. The relation between the fluid flow rate and the bed porosity in a three phase fluidized bed has been obtained by means of effective volumetric flux of fluid from the modification of the Richardson and Zaki's equation.
Effects of gas （4-12 ㎝/s） and liquid (4.0-16.0 ㎝/s) velocities, particle sizes (1.7-8.0 ㎜), and bed porosity on the flow transition of solid have been determined. Water as the liquid phase, glass beads as the solid phase and filtered compressed air as the gas phase have been used in this study.
The modified particle Reynolds Number which describes the effective bulk motions of solid particles and gas and liquid elements exhibited its maximum value with the variation of bed porosity in a three phase fluidized bed. The drag coefficient which is the ratio of drag per unit projected area of particle to the velocity head changed its slope apparently at the bed porosity where the maximum modified particle Reynolds Number could be obtained.
From literatures, immersed heater-to-bed heat transfer coefficient, wall-to-bed heat transfer coefficient, radial mixing coefficient of liquid phase were found having maximum values at these flow transition conditions in three phase fluidized beds.