Abstract

The objective of this work is to propose a decision-making tool for the choice of the drying air velocity in thin-layer drying. Formulated as a physical contradiction, the air velocity should be low to promote heat and mass transfers between the air and the cassava slice, and it should be high for humid air extraction and hot air admission in the drying room. Nine cassava slices were dried at T= 25°C, Rh = 10% with a parallel air flow. Three values of the air velocity were used in three different experiments: 0, 0.3 and 0.6 m/s. Data obtained were fitted with the Newton model, values of R² were: 0.9988, 0.9981 and 0.9976, decreasing with increasing air velocity. The same data were fitted with the Wangh and Singh model, values of R² were: 0.9923, 0.9974 and 0.9984 increasing with increasing air velocity. Therefore, the air velocity should be less than 0.6 m/s based on Newton model, to promote the vaporization of liquid moisture and its uptake, and greater than 0.6 m/s based on Wangh and Singh model, to promote air renewal in the drying room. 

Key words: Cassava, thin-layer drying, air velocity, physical contradiction.