−− Many processes in food technology involve water migration from or into the processed product. Modeling of food water migration knowledge could result speeding up the processes, improving the quality of final products, and reducing energy costs. A mathematical formulation for mass transfer during drying and hydration of a porous solid sphere with volume change was developed in terms of the di...

Preasymptotic transport of a scalar quantity passively advected by a velocity field formed by a large-scale component superimposed on a small-scale fluctuation is investigated both analytically and by means of numerical simulations. Exploiting the multiple-scale expansion one arrives at a Fokker-Planck equation which describes the preasymptotic scalar dynamics. This equation is associated with ...

The advection-diffusion equation for the concentration of a tracer may be transformed into a pure diffusion equation by using the area inside concentration contours as a coordinate. The corresponding effective diffusivity depends on the geometry of the tracer field, which is determined by the underlying flow. Recent studies have used effective diffusivity, calculated from a suitable tracer, as ...

The formal solution to the diffusion equation for transient adsorption in a semiinfinite medium with a strongly concentration dependent diffusivity, originally derived by Fujita ( 3 , has been extended to desorption. Profiles for adsorption and desorption are compared and simplified asymptotic expressions which are useful when the diffusivity ratio is large are derived. The effect of a strongly...

The general quasi-linear autonomous fourth order diffusion equation ut = −[G(u)uxxx + h(u, ux, uxx)]x with positive variable diffusivity G(u) and lower-order flux component h is considered on the real line. A direct algorithm produces a general class of equations for which the Shannon entropy density obeys a reaction-diffusion equation with a positive irreducible source term. Such equations may...

In the present work, the effective moisture diffusivity and activation energy were calculated using an infinite series solution of Fick’s diffusion equation. The results showed that increasing drying temperature accelerated the drying process. All drying experiments had only falling rate period. The average effective moisture diffusivity values varied from 2.807x10 to 6.977x10m s over the tempe...

An explicitly time dependent equation for the alpha-effect in mean field dynamo theory is employed to ensure that the magnetic helicity equation for the total (small and large scale) magnetic field is obeyed exactly. The dependence of the turbulent magnetic diffusivity on the field strength is unconstrained by magnetic helicity conservation and is therefore employed as a free parameter. The app...