ABSTRACT To have a fundamental understanding of the operation of rotary dryers in view of obtaining high quality products and minimizing costs, knowledge of solids transportation, and heat and mass transfer is required. In this paper, the mechanisms of heat rotary dryers are first examined. Based on the underlying principles, the heat transfer models were classified into four categories: the empirical model, the penetration model, a series of perfectly mixed subsection models, and the quasi–3D model. Mass transfer models were also reviewed. Each category of the models was briefly presented and discussed. Some experimental data obtained in a pilot-scale rotary dryer were used to investigate the influence of the feed solids moisture content and gas temperature on the heat and mass transfer and to estimate the volumetric heat and mass transfer coefficients. As expected, a higher inlet gas temperature led to a higher drying rate but it was found that the volumetric heat and mass transfer remained relatively constant. Mass transfer coefficients obtained with the Chilton-Colburn analogy were in close agreement with experimental values.
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