Heat transfer in horizontal solid–liquid pipe flow

An experimental study of the heat transfer coefficient associated with solid–liquid mixture transport was carried out using an electro-resistance sensor and infra-red imaging. The average heat transfer increases with particle concentration. The local value of the heat transfer coefficient is strongly influenced by the cross sectional distribution of the solid phase in the pipe. At flow regimes associated with low mixture flow rates and substantial settled bed, the heat transfer at the bed periphery deteriorates because of the “screen effect” produced by the settled particles. In some cases, this phenomenon may cause local overheating. The analysis of the near wall structures, obtained from the temperature field, has shown that at a relatively high velocity where the bed is thin and flat the streaky structure is close to the one observed in a single phase flow, while at low mixture velocities, where the bed is thick and well packed the typical streaky structures of clear water are destroyed. It is shown that the modified Boltzman function fits the concentration profiles for the case of a moving bed regime. Good agreement is found between the bed height, obtained from experimental data, and the one predicted by the three-layer model.