贝肉真空冷冻干燥过程的数值计算

Numerical Calculation During Vacuum Freeze-drying of Shellfish Meat

本文通过质量和能量衡算,建立了描述冷冻干燥过程的一维非稳态耦合热质传递动力学模型。利用"变时间步长"和"隐式差分"的数值计算方法,将微分方程组的求解化为代数方程组的求解,得出制品升华干燥时间及温度分布情况,并通过实验验证数值解法的可靠程度。计算结果表明,冻结层的有效导热系数远大于干燥层,热量通过冻结层传递到升华界面比通过干燥层快得多。为了证明模型的可行性,实验以7mm的墨西哥湾扇贝柱为研究对象,干燥箱内压力定为10Pa,辐射板温度30℃,搁板温度-22℃。模拟出的升华干燥时间与实验得出的升华干燥时间误差为10%,模拟制品中心温度曲线与实验测得的制品中心温度曲线吻合良好,说明对于形状扁平的水产贝类产品,所选的一维传热模型可以用来预测升华干燥时间。

A dynamic model is developed to describe freeze- drying by mass and energy balance.By making use of numerical calculation method of variable time steps and implicit difference and using Gauss - Seidel iteration algorithm, it converts solutions of differential equations into those of algebraic equations to obtain the time of material sublimation- dry- ing stage and its temperature distributing; experimental conditions are designed to verify the dependability of numerical solutions.Results of computation show that equivalent thermal conductivity of frozen layer is far mere than that of dry layer, and heat of wansferring to sublimation interface through frozen layer is faster than that through dry layer.For verifying the feasibility of model, the experiment is done： material thickness 7 mm, chamber pressure 10 Pa, temperature of radiation board 30℃, temperature of heating beard - 22℃. The error between predicted sublimation - drying time and experimental time is 10%, and the predicted values of central temperature of material are in good agreement with experimental values, all show that heat - transfer model of one - dimension can be used to predict the drying time of tabular shellfish meat during sublimation- drying stage.