冻结方式对预冻甘露醇冰晶粒度分布的影响

来源期刊:中南大学学报(自然科学版)2019年第7期

论文作者:刘志强 贾颖姣 罗春

文章页码:1704 - 1712

关键词:计算流体力学;粒度分布;相变;冻结;均匀度

Key words:computational fluid dynamics; particle size distribution; phase change; freezing; uniformity

摘    要:基于真空冷冻干燥过程中冰晶粒度的分布对干燥过程以及冻干产品的品质具有重大影响,为此,模拟研究搁板温度恒定、从常温匀速降温以及含养晶过程的恒温降这3种冻结方式对冰晶粒度分布的影响。研究结果表明:搁板恒定低温和匀速降温条件下西林瓶的高度方向呈中间大两端小;当各冻结方式中温度条件变化时,搁板温度越低,则冰晶粒度越细密、越均匀;而且较大的降温速率也会产生细密且分布均匀的冰晶。当取恒定温降的最终温度等于恒定搁板温度时,恒定温降条件下的冰晶粒度比恒定搁板温度条件下的粒度平均值更大,但前者产生的冰晶粒度分布更均匀;若在恒定温降条件中加入养晶过程,则冰晶平均粒度会增加,且可通过调节养晶时间调控分布的均匀度。

Abstract: The distribution of ice crystal grain size has a significant effect on the drying process and the quality of freeze-dried products. Three freezing methods, i.e., keepingg the shelf at a constant temperature, cooling from room temperature at a constant cooling rate, and cooling at a constant cooling rate containing crystal growing process, were proposed. Effects of three different freezing methods on the size distribution of ice crystal were investigated. The results show that when products are cooled at the shelf with constant temperature or cooled at a constant cooling rate, large ice crystals are found in the middle of the vial while small at the extremity. Moreover, when temperature changes, the lower the temperature of the shelf is, the tinier and more uniform the ice crystal is, and larger cooling rate leads to tinier ice crystals with more uniform distribution. Furthermore, when the final temperature of cooling at constant rate is the same as the temperature of shelf, the size of crystals generated by the former methods is larger than that produced by the latter methods while it is with the more uniform distribution. If the crystal growing process is added into the cooling at constant cooling rate, the mean size of ice crystal would increase,and the uniformity of the distribution can be regulated by controlling the time of crystal growing.

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