Pulsating the flow in a fluidized bed by using a moving double plate distributor (MDPD) lo control the bubble size and enhance the fluidization characteristics is a new approach. In this novel design, a second plate Is placed under the existing distributor such that it can make a reciprocating motion generating pulses to the flow field. The frequency and amplitude of the pulsation can be adjusted to break up the large bubbles in the bed. The aim of this study is to investigate the effect of pulsation on the bubble size, bubble speed, bubble fraction and bed expansion in a fluidized bed. For this purpose, the bubbles were followed two-dimensional fluidized bed with turnip seed and sand as the bed material for different pulsation frequencies and operating velocities. Bubble size, speed and bed expansion were measured for pulsed flow and compared with those of continuous flow. Image processing techniques were utilized to measure the bubble fraction. Interesting bubble flow patterns were observed and a significant decrease in bubble size was achieved for the pulsed flow. (C) 1998 Elsevier Science S.A.