Numerical simulation of contact vacuum drying of potato slices

Abstract

• A mathematical model for contact vacuum drying is numerically solved. • The simulations predict the drying kinetics coupled to the pressure changes in the chamber. • The frequency of active/passive phases depends on the mass flux, which is linked to the free moisture content of the samples. • Vacuum drying reveals to have a larger impact in the first period of drying. In this work, a mathematical model is proposed to simulate the Contact Vacuum Drying of potato slices. Three temperatures were analyzed: 55, 65, and 75 °C with three levels of vacuum pressure: 60, 40, and 20 mmHg. In the macroscopic model, the boundary condition for the moisture conservation is written in terms of water vapor pressure, and it considers the dynamics of the vapor pressure in the chamber. The simulations predict the evolution of gas pressure and the drying kinetics. As drying occurs, the passive regime is prolonged as a result of a decrease in the moisture content. The maximum drying rate (1.4 E-3 kg. water/kg. dry solid·s) corresponds to the drying condition at 75 °C and 20 mmHg, which is the most intensive drying condition. The comparison between the predicted and experimental values showed acceptable agreement. The simulations correctly represent the drying kinetics and the evolution of the gas pressure in the drying chamber.