对流干燥过程理论分析:水分活度

Theoretical Analysis of Convective Drying Process:Water Activity

在收缩和非收缩条件下,对胡萝卜的对流干燥特征进行了理论分析。结果表明,干燥速率是试样几何形状、尺寸以及热空气温度、风速、相对湿度的函数。整个干燥过程应划分为外部干燥条件控制的第一干燥阶段和物料内部水分扩散控制的第二干燥阶段。而基于经典干燥理论的恒速干燥阶段和降速干燥阶段的划分,只是特定形状和材质的物料在一定干燥条件下才出现的干燥现象。物料外层单元水分活度可以作为判别物料干燥过程是处于第一干燥阶段还是第二干燥阶段的判断依据,是表征物料干燥特性的特征参数。

A theoretical analysis is carried out to study the convective drying characteristics of carrot under shrinkage and non shrinkage. The results show that the drying rate of sample is a function of shape of samples, dimension of samples, and temperature, velocity, relative humidity of hot air. The whole drying process should be divided into the first drying process controlled by the external drying condition and the second drying process controlled by the internal water diffusion of the material, rather than the constant drying rate process and the falling drying rate process described in the classical drying theory. Furthermore, the characteristic parameter judging whether the drying process is in constant drying rate stage or in falling drying rate stage is the external element＇s water activity.