空气与静水环境下速冻荔枝解冻过程的数值模拟

Numerical Simulation of Air Thawing and Still-water Thawing of Quick-frozen Litchi

摘要:

为了探究空气与静水环境下速冻荔枝解冻过程的内部温度变化与解冻完成时间，该研究采用数值模拟结合试验验证方法对其进行分析。结果表明：荔枝在解冻过程中的热物性参数主要受到其水分含量尤其是冰-水相变过程的影响。数值模型能够较为准确的预测荔枝解冻期间的温度变化规律，空气解冻组与静水解冻组的均方根误差（Root Mean Squared Error, RMSE）分别为2.02 ℃和1.79 ℃，二者解冻时间的实测值与模拟值偏差分别为2.32%和1.50%；相比空气解冻，静水环境下荔枝的果皮、果肉和果核的解冻时间分别缩短了93.33%、74.94%和69.25%；荔枝横纵径尺寸越大、解冻介质的温度与换热系数越高，荔枝的解冻完成时间越短，但是内部温度的均匀性也会越差，另外荔枝的解冻速率不仅取决于解冻介质与果实的换热效率，还会受到荔枝果实内部导热性能的影响。简言之，在确定荔枝的化学组成与热物性参数后，速冻荔枝的解冻过程能够实现良好的数值模拟，另外荔枝的横纵径尺寸、解冻环境的温度与换热系数会影响荔枝的解冻特性。

Abstract:

The thawing of quick-frozen litchis in air and still-water environments was analyzed via numerical simulation and experimental verification by monitoring the internal temperature changes and thawing time. The thermal properties of litchis during thawing, especially the ice-water phase transition, were mainly influenced by the moisture content. The temperature changes of litchi during the thawing period could be accurately predicted using the numerical model. The root mean square error (RMSE) for the air-thawed group and the still-water-thawed group was 2.02 and 1.79 ℃, respectively. The measured and simulated thawing times for the two groups had deviations of 2.32% and 1.50%, respectively. Compared with air thawing, the thawing time of litchi peel, pulp, and core in the still-water environment was shortened by 93.33%, 74.94%, and 69.25%, respectively. The larger the horizontal and vertical diameters of litchi, the higher the temperature and heat transfer coefficient of the thawing medium, and the shorter the thawing completion time, whereas the internal temperature was less uniform. The thawing rate of litchi depends not only on the heat exchange efficiency between the thawing medium and the fruit, but also on the internal thermal conductivity of the litchi fruit. In summary, after determining the chemical composition and thermal properties of litchi, the thawing of frozen litchi was effectively analyzed through numerical simulation. Thawing is also affected by the horizontal and vertical diameters of litchi and the temperature and heat transfer coefficient of the thawing medium.