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 e †ect of the slip velocity on the particle velocity and the calculated values of solids circulation rate was also investigated.1998 SCI (

The presence of solid particles in a heat exchanger is important in keeping the surface clean, thus having a beneücial eþ ect on heat transfer. Solids circulation in the system can be provided by means of a recycle tube mounted in the central core of the heat exchanger. In this study a pilot scale ýuidized tube heat exchanger system which consists of six ýuidization tubes together with the centrally located recycling tube was constructed and pressure drop, liquid-wall and solid-wall friction forces and the eþ ects of the amount of solids introduced to the system on heat transfer were investigated. Experimental results indicate that although the recycle tube causes an approximately 35% decrease in the heat transfer coefficient when no solid is used, the presence of the solids in the system increases the heat transfer coefficient by about 45% above that of the solids-free system.

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