Comparison of residence time models for cascading rotary dryers

The predictions of the models of Matchett and Baker (1988), Saeman and Mitc hell (1954) and Friedman and Marshall (1949) for the solids residence time in rotary dryers have been compared with both pilot-scale and industrial-sc ale data. A countercurrent pilot-scale dryer of 0.2 m diameter and 2 m long has been used with air velocities up to 1.5 ms(-1) to measure the residenc e times of sorghum grain. The average discrepancy for the solids residence time between the predictions and the experiments that were carried out in t he pilot-scale rotary dryer is -10.4%. Compared with the models of Friedman and Marshall (1949) and Saeman and Mitchell (1954) for the pilot-scale dat a obtained here, the Matchett and Baker model is more satisfactory for pred icting the solids residence time in this pilot-scale dryer. It has also bee n found that the model of Matchett and Baker describes the industrial data of Saeman and Mitchell (1954) than the correlation of Friedman and Marshall (1949).