A mathematical model based on mass and heat balance equations was developed for simulating atmospheric freeze-drying of food products. When fresh fruit slices are freeze-dried at temperatures far above the glass transition temperature, structural deformation and melt-back would occur due to the glass-rubber-liquid transition. Based on this observation, an atmospheric freeze-drying system was modeled by considering the in-drying product as a uniform mixture of the rubber/liquid and ice phases that could exhibit a specific vapor pressure. Temperature- and moisture content-dependent apparent vapor pressures of the apple slices were obtained experimentally and plotted in a diagram. Notably, the apparent vapor pressure was significantly different from the vapor pressures of pure water/ice at the corresponding temperatures, particularly at around the glass transition curve. The simulation was implemented with the developed single zone model by applying these obtained apparent vapor pressures. This approach could predict drying kinetics with reasonable accuracy and simplified equations. The parameters applied in this simulation were further confirmed to be applicable to various operating conditions (air temperature from –10 to 10 ºC; air flow rate from 0.1 to 0.5 m/s).

建立了基于质量和热量平衡方程的数学模型，用于模拟食品的大气冷冻干燥。当新鲜水果切片在远高于玻璃化转变温度的温度下冷冻干燥时，由于玻璃-橡胶-液体转变，会发生结构变形和回熔。基于此观察结果，通过将待干燥产品视为橡胶/液体和冰相的均匀混合物来建模，以模拟常压干燥系统，该橡胶/液相和冰相可能呈现特定的蒸气压。通过实验获得了与温度和水分含量相关的苹果切片的表观蒸气压，并绘制了图表。值得注意的是，在相应温度下，表观蒸气压与纯水/冰的蒸气压显着不同，特别是在玻璃化转变曲线附近。通过应用这些获得的表观蒸气压，利用已开发的单区模型进行了仿真。这种方法可以以合理的精度和简化的方程式预测干燥动力学。进一步证实了在此模拟中应用的参数适用于各种运行条件（气温从–10到10ºC；空气流速从0.1到0.5 m / s）。