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Flowproperties in a dissolver for direct coal liquefaction were simulated by using a cold bubble column of 12 cm i.d. To generate small gas bubbles in the column, a surfactant was added to tap water and a gas distributor with fine holes was employed. Whenglass spheres of 44 and 113 /nn dia. were suspended in the presence of the surfactant, the gas holdup was 1.5-4 times that for the tap water system, and the axial dispersion coefficient of liquid showed a minimum at superficial gas velocities of 3-5 cmà"s~*. Themeansettling velocity of solid particles, vp, wasaffected by the quality of flow in addition to gas velocity and terminal velocity of solid particles. Most values of vp obtained in this experiment were larger than those for the tap water system where no fine gas bubbles were generated. Experimental equations for the correlation of vp are presented. An introduction of secondary gas in the homogeneous bubble flow regime effectively increased the axial liquid mixing. This suggests that in the design of a dissolver quenching gas injection is important to attain spontaneous discharge of ash particles from the top of the vessel.