Drying modelling and water diffusivity in carrots and potatoes

Modelling is a useful way to validate mechanisms of drying and to establish properties, and thus can be used to determine the reliability of calculated values of the effective diffusivity (De). Diffusive models are considered for the description of convective drying of particulate vegetables (carrots and potatoes). Four models with different degrees of complexity are discussed. The degree of complexity depends on consideration of shrinkage, heat transfer and particle temperature variation during drying, and the De dependence on moisture and temperature simultaneously. Experiments have been carried out to test the models and the assumed boundary conditions. Experimental results show that the effect of shrinkage cannot be neglected in establishing reliable values for De. The effect of the external resistance, which is affected by the velocity of the air used in drying, also appears to be an important factor for testing De values. Two methods are proposed to carry out this test, both of which could be readily applied if the drying curve is available. Experiments on drying carrots and potatoes are used to illustrate the procedures.