Air drying of vegetables: Evaluation of mass transfer coefficient

A new equation for the external mass transfer coefficient during vegetable drying is presented. The equation is validated for carrot slices dried under natural convection conditions. A finite element method is used to solve the non-linear boundary value problem modelling the carrot drying process. The mean value of the mass transfer coefficient is 1.371 x 10(-7) ms(-1) during the initial phase of ms drying 4-mm-thick fresh carrot slices in air at 60 degrees C. It is concluded that the Neuman-type boundary condition for mass transfer during carrot drying gives a much better fitting of measured results to the computer simulation results than does the Dirichlet-type one. The Dirichlet-type boundary condition used for simulation of the process of carrot drying under natural convection conditions may lead to unrealistic results. (C) 1998 Elsevier Science Limited. All rights reserved.