Heat Transfer in a New Type of Heat Exchanger for Divided Solids

Artikel i vetenskaplig tidskrift, 1979

A new type of horizontal, rotating drum heat exchanger is described, which is intended for indirect heat transfer between two streams of solids or for indirect cooling or heating a stream of solids. The heat exchanger is baffled internally and the baffles have three purposes: a transport of the solids, enlargement of the heat transfer area and agitation of the particulate bed in order to achieve good mixing. Rates of heat transfer were measured for streams of four kinds of solids material: two types of sand, glass beads and steel shot. The rate of heat transfer-increased with increasing speed of rotation and fill of the particle bed. The mean particle diameter was the most important of the particle properties. Overall heat transfer coefficients were found to be higher than for most other types of indirect heaters and coolers for solids. A model of the heat transfer process is presented in which the whole resistance to heat transfer is assumed to be in the particle layers in the vicinity of the heat transfer wall. This resistance consists of two parts, one time-independent between the wall and the bed and one time-dependent in the bed itself. The model is shown to be capable of predicting the rates of heat transfer accurately.