Abstract:

By discretizing the population equation into different size groups, a method was established for solving the population balance equation coupled with multiphase flow field.A computational fluid dynamics simulation with population balance model was performed for the scraped surface freezer.The algorithm considering nucleation rate, growth rate, crystal aggregation and breakage was used for describing the water dynamic ice-making crystallization process.By using this model, the key role of crystal aggregation and breakage was reappraised, and the ice crystals number density distributions were obtained in the scraped surface freezer.Then the influence of temperature, scraping speed and the crystallization time on the dynamic crystallization process of the water was studied.The results show that the crystal size distribution would be more centralized and uniform with the crystals aggregation and breakage; if the supercold temperature difference is less than 20℃ and the scraping speed is not more than 10 r·s^-1, the crystallization process would be accelerated by reducing the wall temperature or increasing the scraping speed.

Key words: phase change, multiphase flow, model, population balance, crystallization, number density, aggregation and breakage

摘要：

在考虑晶粒成核、生长、聚并和破碎的情况下，采用分组法求解粒数衡算方程，通过耦合粒数衡算与多相流方程，建立了多尺度的结晶模型，模拟了表面刮削式制冰装置内水的动态结晶过程，获得不同温度、刮削速度、制冰时间等外界条件下晶粒数密度分布、云图等信息，分析了外界宏观条件对水的动态结晶过程的影响。结果表明：由于碰撞引起的晶粒聚并和破碎使得晶粒的尺寸分布更为集中和均匀；在过冷温差（流体局部温度与水的相变温度差值）不大于20℃，刮削速度不大于10 r·s^-1范围内，降低壁面温度、增加刮削速度可以加速水的结晶与生长。

关键词: 相变, 多相流, 模型, 粒数衡算, 结晶, 数密度, 聚并和破碎