DRYING MODELING AND WATER DIFFUSIVITY IN CARROTS AND POTATOES

Modelling is a useful way to validate mechanisms of drying and to esta blish properties, and thus can be used to determine the reliability of calculated values of the effective diffusivity (D(e)). Diffusive mode ls are considered for the description of convective drying of particul ate vegetables (carrots and potatoes). Four models with different degr ees of complexity are discussed. The degree of complexity depends on c onsideration of shrinkage, heat transfer and particle temperature vari ation during drying, and the D(e) dependence on moisture and temperatu re simultaneously ExPeriments have been carried out to test the models and the assumed boundary conditions. ExPerimental results show that t he effect Of shrinkage cannot be neglected in establishing reliable va lues for D(e). The effect of the external resistance, which is affecte d by the velocity of the air used in drying, also appears to be an imp ortant factor for testing D(e) values. Two methods are proposed to car ry out this test, both of which could be readily applied if the drying curve is available. Experiments on drying carrots and potatoes are us ed to illustrate the procedures.