A lumped parameter model for effective moisture diffusivity in air drying of foods

During drying of foods, the moisture diffusivity depends on several factors like the moisture content, temperature and the degree of shrinkage of food materials. As an approximation, the effects of these factors on moisture diffusivity are lumped together and expressed in terms of an effective moisture diffusivity, which is considered an explicit function of Fourier number (i.e. drying time). The kinetics of moisture removal during the drying of green mango was investigated in a through-circulation dryer. From the analysis of experimental results, three different types of functional dependency [i.e linear (L), exponential (E), and exponential followed by two linear regimes (ELL)] of the effective moisture diffusivity on Fourier number have been used to model the drying kinetics observed in the current study. Moisture distribution during the drying has been calculated using Fick's law with constant diffusivity, as well as the developed models. Computational analysis shows that the ELL model yields a better prediction of the experimental results than the other two models. To determine temperature-independent values of the ELL model parameters, linear and exponential relationships between the model parameters and temperature for each drying regime have also been considered. Comparison with the experimental results shows that the ELL relationship between the effective moisture diffusivity and Fourier number followed by a linear dependency of the ELL model parameters on temperature, predict the drying behaviors fairly well (R-2 > 0.96) for the system conditions studied in the current investigation.