Considering the application of the technique of liquid spouting with multi draft tubes to heat exchangers, the solids circulation rate was studied both experimentally and theoretically. It was found that the solids circulation rate increased with the liquid velocity and with the amount of solids used. Experimental results were found to be lower than the calculated values. It was concluded that the friction forces between closely packed particles and between particles and the wall of the return pipe at the zone of entrainment retard the solids circulation rate. The rate of the calculated to the experimental circulation rates was observed to be lower as the concentration of solids increased. The effect of the slip velocity on the particle velocity and the calculated values of solids circulation rate was also investigated. (C) 1998 SCI.