Mathematical modeling of the primary and secondary vacuum freeze drying of random solids at microwave heating

This paper presents a complex model of the primary and secondary vacuum freeze-drying stages at microwave heating. The simulation of the process was performed for typical adsorbents which were chosen as ideal representatives of random solids having particle and bed porosity. One-dimensional two-region model of the primary freeze-drying at microwave heating was formulated and then solved numerically using the finite-difference MacCormack method. Varying during the process sublimation front temperature Ts(t) was taken into account. Simulated drying curves were compared with experimental results giving fairly good agreement. A mathematical model of the secondary freeze-drying at microwave heating was developed and solved using the numerical method of lines. Pressure drop in the material was taken into account and calculated using Ergun equation. As a result of the model solution, the moisture content and the temperature distributions in drying material were obtained. In both mathematical models steady internal heat source capacity was calculated as a function of material temperature.