基于分形理论的火龙果冻干过程数值模拟

目的:分析火龙果冻干过程的干燥特性。方法:基于分形理论和多孔介质传热传质理论,使用COMSOL软件对厚度为8,10,12,14 mm,半径为40 mm的红心火龙果片进行数值模拟,模拟火龙果升华干燥阶段火龙果内部多孔介质内的传热传质过程,获取冰升华过程中冰界面的实时位移,预测升华周期,并进行实验验证。结果:模拟数据与试验数据相吻合,误差较小,脱水速率最大相对误差为12.6%,绝对误差为0.18 g/h;含水率最大绝对误差为5.4%。相同初始速冻温度下,随着厚度的增加,升华干燥阶段时间呈非线性增加;火龙果内部孔隙直径越大,有效扩散系数越大,干燥速度越快,产品品质随之下降。结论:基于分形理论能够实现良好的火龙果冻干过程的数值模拟,综合考虑冻干产品制造周期和品质,10 mm为红心火龙果的最佳厚度。

Numerical simulation of pitaya freeze-drying process based on fractal theory

Objective: To optimize the drying characteristics of dragon fruit freeze-drying process. Methods: Based on the fractal theory and the theory of heat and mass transfer in porous media, the COMSOL software was used to numerically simulate red pitaya slices with a thickness of 8, 10, 12, 14 mm and a radius of 40 mm to simulate the sublimation and drying stage of pitaya. The heat and mass transfer process in the internal porous medium, the real-time displacement of the ice interface during the ice sublimation process is obtained, the sublimation period is predicted, and the experimental verification is carried out. Results: The simulated data were in good agreement with the experimental data, and the error was small. The maximum relative error of dehydration rate was 12.6%, and the absolute error was 0.18 g/h; the maximum absolute error of water content was 5.4%. Under the same initial quick-freezing temperature, with the increase of thickness, the time of sublimation drying stage increases nonlinearly; the larger the pore diameter of dragon fruit, the larger the effective diffusion coefficient, the faster the drying speed, and the lower the product quality. Conclusion: Based on the fractal theory, a good numerical simulation of the freeze-drying process of dragon fruit can be achieved, and 10 mm is the optimal thickness of red dragon fruit.