Numerical solution of diffusion equations with strongly variable diffusion coefficients. Calculation of flavor loss in drying food liquids

The loss of volatile org. components in drying food liqs. is to some extent governed by the simultaneous flux of water and is stronly influenced by the different ways in which the diffusion coeffs. of the volatile components and of water depend on the water concn. The strong water concn. dependence of the diffusion coeffs. makes an anal. soln. of the diffusion equations describing the mass transfer in the drying product impossible. However, if the drying system does not have too complex a geometry the diffusion equations can be solved numerically. Because of the very steep concn. gradient near the evapg. surface, the implicit (as well as explicit) standard numerical calcn. procedures require a lot of computer time. A new numerical method is discussed in this paper. With this method the drying rate curve and volatile component retention were calcd. for a slab composed of water and maltodextrin to which acetone was added as a model org. volatile. The calcd. retentions of water and acetone fit the exptl. data within the accuracy of the observations. [on SciFinder (R)