The first period of convection drying of vegetables and the effect of shape-dependent shrinkage

Research on the kinetics of convection drying of vegetables has shown that the first period of drying exists, and non-linear changes in water content of the vegetables occur. The non-linear changes in the water content result from shrinkage of the drying materials. A mathematical, non-linear theoretical model for the first period of drying contains a coefficient N, the value of which depends on the surface shrinkage of the dried material. Up to now, the value of N has been determined by a process of trial and error. In this paper, a method is presented for determining the value of the coefficient N analytically for cut vegetables. Models for the coefficient N for bodies having the shape of either a cuboid or a circular cylinder are formulated. For cut vegetables, the value of the coefficient N can also be determined by the Monte-Carlo method, using a reversed distribution function of the coefficient N treated as a random variable, and established on the basis of its empirical distribution. This method can be useful in practical applications. The proposed models were verified empirically for cut vegetables, such as garden beet and carrots. (C) 2002 Silsoe Research Institute.