基于材料透气性参数的食品真空冷却过程中温度分布的理论研究

Theoretical Study of Temperature Distribution of Food During Vacuum Coding Process Based on Permeatghity Parameter

分析了真空冷却过程中食品温度分布不均匀的原因。以各向同性的理想食品作为研究对象,通过引入食品材料透气性参数,将食品内部点的汽化转化为食品表面的汽化,推导出真空冷却过程中食品各部分温差的表达式。在此基础上,探讨了各相关参数对温度分布的影响。结果表明:食品的比热容、沸腾系数和密度影响温度下降的速度,但是对达到预定温度时的总温差没有影响;提高食品的透气性参数值和减小食品内部点到表面的最短距离,可以减小温差;可以通过调节真空室的压力变化,提高食品温度分布的均匀性。

The causes of temperature difference of food various parts during vacuum cooling process were detected. By the introducing air permeability of food material and transforming the evaporation in the internal into that on the surface of food, the expression of the temperature difference of isotropic food various parts during vacuum cooling process were obtained. On this basis, the factors affecting the temperature differences were analysed by the expression. The results showed that boiling heat transfer coefficient and specific heat capacity and density could affect the velocity of temperature difference change. However, these parameters had no influence on overall temperature difference when the temperature was meeting the preset value. Enhancement of the food permeability parameter value could increase the temperature uniformity. The shorter the shortest-distance from internal point to the surface is, where the smaller temperature difference is. Furthermore, temperature uniformity could be enhanced through regulating the vacuum pressure change.