Research of the Effective Diffusion Coefficient and Activation Energy for the Purpose of Energy Saving during Convection Dryin

In this study, the calculation and mathematical modelling of effective diffusion coefficient and activation energy in convective drying of a product were investigated. The shrinkage coefficient for different temperatures was also calculated. The effective diffusion coefficient was calculated using Fick’s law developed for finite cylindrical geometry. Using the effective diffusion coefficient equation for air temperatures of 45, 55 and 65 °C, the results were obtained as 2.02 ∙ 10^–10, 5.05 ∙ 10^–10 and 8.08 ∙ 10^–10 m²/s, respectively. The activation energy was calculated as 61.1 kJ/mol using the slope of the graph ln(D_ef)^–1/T. The product shrinkage coefficients at drying air temperatures of 45, 55 and 65 °C were found to be approximately 23, 32 and 40 %, respectively. In order to find the most suitable mesh structure of the model, a network independence study was carried out using average moisture content values with an accuracy of 0.001. Nonlinear simultaneous heat and mass transfer equations for 45, 55 and 65 °C dehumidifying air are solved by the finite element method (MATLAB) with initial and boundary conditions. The equations are solved with a tolerance value of 0.001 for thirty minutes time steps. The initial conditions used in the analyses and the thermophysical properties of the product are detailed in tables and graphs. The data obtained from the experimental and numerical solution were compared and it was seen that the results were compatible with each other. According to this result, a mathematical model expressing simultaneous heat and mass transfer can be used to predict the moisture and temperature distribution in the product during drying.

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