Microwave-vacuum drying kinetics of carrot slices

The kinetics of microwave vacuum drying of thin layer carrot slices was studied by introducing a theoretical model. The model is based on the energy conservation of sensible heat, latent heat and source heat of microwave power. The model was tested with data produced in a lab microwave-vacuum dryer in which the materials to be dried could rotate in the cavity. The theoretical and experimental drying curves showed that the theoretical model was in agreement with experimental data, and drying rate was a constant until the dry-basis moisture content X-s was about 2. As 1 less than or equal to X-s < 2, the experimental drying curves showed a little deviation from the theoretical drying curves. While X-s < 1, the experimental drying curves showed a sharp deviation from the theoretical drying curves. To predict the changing of moisture content with time by the theoretical model in the period of X-s < 2, a correction factor, phi, was introduced and obtained using non-linear regression analysis. The investigation involved a wide range of microwave power and vacuum pressure levels. Both the theoretical model and experimental data also showed that the drying rate was linear to the microwave power output, and inversely proportional to the first order of latent heat of evaporation for water at the vacuum pressure of P. (C) 2004 Elsevier Ltd. All rights reserved.