The presence of solid particles in a heat exchanger is important in keeping the surface clean, thus having a beneficial effect 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 fluidized tube heat exchanger system which consists of six fluidization tubes together with the centrally located recycling tube was constructed and pressure drop, liquid-wall and solid-wall friction forces and the effects 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. (C) 1999 Society of Chemical Industry.