收缩和非收缩条件下,对胡萝卜对流干燥特征进行了理论分析.发现临界水分质量比是试样几何形状、尺寸大小以及热空气温度、速度、相对湿度的函数.在收缩条件下,只有薄片状试样对流干燥过程包含恒速干燥阶段和降速干燥阶段；而圆柱状和球状试样干燥速率从干燥起始就随试样水分质量比的下降降低.数值实验结果表明,根据物料临界水分质量比很难确定对流干燥过程处于外部干燥条件控制的第1干燥阶段还是物料内部条件因素控制的第2干燥阶段.临界水分质量比不是表明物料干燥特性的特征参数.%A theoretical analysis was carried out to study the convective drying characteristics of carrot under shrinkage and non-shrinkage. The critical moisture mass ratio was found to be function of shape of samples, dimension of samples, and temperature, velocity, relative humidity of hot air. It shows that only slice sample contains constant drying period and falling rate period under shrinkage. On the contrary, the drying rates of cylindrical and spherical samples decrease with moisture mass ratio at the beginning of drying. The numerical results indicate that the critical moisture mass ratio is not the characteristic parameter for identifying the drying process whether in constant drying rate stage or in falling drying rate stage. The critical moisture mass ratio isn't the characteristic parameter that describes the drying process of wet materials.
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