MATHEMATICAL-MODELING OF INDIRECT CONTACT ROTARY DRYERS

Two different approaches were used to predict the solid moisture conte nt and solid temperature profiles along a continuous indirect contact rotary dryer heated with steam tubes. One of these uses heat and mass balances applied to the solid phase in a differential element of dryer length. Here the heat flux is computed through an overall heat transf er coefficient assumed constant. The other model is based on a previou s work that calculates the heat transfer coefficient as a function of the time the solid particles are in contact with the heating surface. The advantage in using this second model lies in the fact that the cal culated heat transfer coefficient can take into account the effects of the operational conditions. If this coefficient has a strong dependen ce on these conditions, then it would be inappropriate to use a fixed value. Although both approaches can predict the solid moisture content and temperature profiles along the dryer differences were detected.