柱状胡萝卜样品热风微波耦合干燥数学模型

Mathematical modeling of microwave assisted air drying of cylindrical carrot samples

利用热风微波耦合干燥装置研究了柱状胡萝卜样品的干燥特性,一个实验室规模的热风微波耦合干燥装置用来实现此实验目的。基于干燥过程中同时具有传热传质现象,建立了一个数学模型以此来预测干燥过程中样品内温度和含水量的分布。考虑到柱状样品的半径和微波的穿透深度,假定微波中的电场强度在样品内均匀分布。由于表面水分的蒸发而造成的热损失被考虑在内并将其作为模型的一个边界条件,利用数值方法中的隐式有限差分法对模型进行求解。通过干燥尺寸不同的柱状胡萝卜样品得到的实验值和模型的预测值进行比较来对模型进行验证,探讨了微波功率密度和热风温度的影响作用。

Drying behavior of cylindrical samples of carrot was investigated in a microwave assisted air drying. A pilot-scale microwave assisted air dryer was set up for this purpose. Based on the simultaneous heat and mass transfer,a mathematical model was proposed for predicting the temperature and moisture distribution in the drying sample. Considering the carrot radiuses and the penetration depth of the electromagnetic waves,a uniform electric field strength distribution within the drying material was assumed in the proposed model. The heat loss due to surface evaporative cooling was also considered at the external boundaries. A numerical solution was developed for the proposed model using an implicit finite difference method. The model was validated by comparing the predicted data with the experimental data ,obtained from different cylindrical carrot samples during drying. The effects of microwave power density and also drying air temperature on the moisture and temperature profiles were investigated.