马铃薯泥鼓风冷冻数值模拟与实验

Numerical Analysis and Test on Characteristics of Temperature Decreasing of Mashed Potatoes

摘要:

为掌握马铃薯泥在鼓风冷冻过程中的温度变化规律，建立了短圆柱状马铃薯泥鼓风冷冻的三维数值模型，进行了三维非稳态数值模拟，并结合流场及不同时刻的温度场对马铃薯泥的冷冻过程进行了分析。实验验证表明该模型与实际情况吻合较好，冷冻时间相对误差为3.9%。以此为基础，研究了送风速度和温度对马铃薯泥冷冻过程的影响。结果表明，随着风速的提高，冷冻时间缩短，马铃薯泥内外温差增大，冷冻结束时马铃薯泥中心温度之间的差异先减小后增大。降低送风温度可以缩短冷冻时间，增大马铃薯泥中心温度之间的差异性和马铃薯泥内外温差。送风速度和温度对相变阶段的影响大于预冷段和深冷段。

Abstract:

In order to investigate the characteristics of temperature decreasing of mashed potatoes without packages during freezing in an air blast freezer，a three-dimensional unsteady numerical model was established to simulate the freezing process of mashed potatoes. According to the thermo-physical properties of mashed potato, the process of the temperature decreasing during freezing was simulated by Fluent，after which the airflow information in the container was obtained．A test was done to verify the accuracy of the model，and it was found that the simulation values and test values were in good agreement，the maximum temperature difference between the test data and simulation result was 7.1K and the relative error of freezing time was 3.9%. After that，two design parameters (air velocity and air temperature) which would affect the freezing process were analyzed．Improving the air velocity can shorten the time of freezing but would improve the maximum temperature difference between the mashed potato’s core and edge. The variation coefficient of temperature among mashed potatoes was firstly increased and then decreased with the increase of air velocity, and it was minimum when the air velocity was 6m/s. When the air velocity was bigger than 6m/s，the freezing rate trended to be steady along with the growing of air velocity. Reducing the air temperature can effectively improve the temperature decreasing of mashed potatoes during freezing but also would improve the variation coefficient of temperature among mashed potatoes. The results reviewed some characteristics of the freezing of mashed potatoes without packages in an air blast freezer, which can provide a reference value for the optimization of the equipments and technologies for the freezing of foodstuffs．