食品冻干机干燥速率影响因素的分析

Analysis of the factors affecting the drying rate of food freeze dryers

本文从干燥过程的传热与传质机理及溶液结晶理论出发,并结合干燥实验曲线,研究了传热控制下的干燥过程与传质控制下的干燥过程;分析了在这两种过程中影响冻干机干燥速率的各个因素,并针对这两种过程,指出了提高干燥速率的切实可行的措施。结果表明:(1)影响冻干机干燥速率的因素有食品的厚度、干燥箱内气体的绝对压力、升华界面温度、干层表面气体温度、冷阱温度、以及干燥前食品予冻结的方式等。(2)对于传热控制下的干燥过程(一般为干燥前期),提高干燥箱内的绝对压力比较有利,升华界面温度则应低一些;(3)对于传质控制下的干燥过程(一般为干燥后期),则应降低干燥箱内的绝对压力,而升华界面温度则在不超过其崩解温度的前提下应尽可能高;干燥箱内的压力可通过微调真空阀与电磁阀来控制。

Based on heat transfer and mass transfer theory and solution crystallizing theory, with the drying process curve, the paper studies the transfer, analyzes various factors affecting drying drying processes under control of heat transfer and of mass rate during the two processes, and points out the methods to increase drying rate. The results show： （1） the factors affecting drying rate are gas pres- sure in the drying box, the temperature of sublimation surface and water vapor capturer surface and the freezing way before drying; （2） for process under control of heat transfer （ generally at the begin- ning）, temperature of the sublimation surface should be low and increasing the pressure of the drying box is also a good method; （3） for process under control of mass transfer （generally at the later phase）, the pressure of the drying box should be low, temperature of sublimation surface should be high and the pressure in the drying box can be controlled by using a vacuum valve and an electromag- netic valve.