【作者】 章国芳；

【导师】 袁竹林；

【作者基本信息】 东南大学 ， 制冷及低温工程， 2006， 硕士

【摘要】 本文采用数值模拟方法,针对一种新型制取流体冰方法中的关键问题——水在油介质中的雾化特性进行了研究,取得了相应的研究结果和结论。该新型制取流体冰方法的机理是把与水不相溶的低温油介质均匀导入直立的制冰通道中,同时通过特殊设计的雾化装置,将淡水雾化成细小水滴顺流喷入制冰通道的低温油介质中。水滴在与低温油介质混和流动的过程中直接接触换热被冷却直至冻成冰颗粒,从而避免了以往制冰方法中水与固体壁面换热结冰所带来的热阻增大的问题。这个过程是水滴、冰颗粒和油介质的多相流动与换热,其中包括水滴的相变过程。通过水与油介质的分离特性实验本文确定选用25号变压器油作为载冷油介质。根据新型的制取流体冰方法,本文采用欧拉-欧拉数值模拟方法将水相和油相处理成连续介质,对水在油介质中的雾化建立VOF模型,追踪水相与油相之间的运动界面,观察水在喷口处形成雾化水滴并长大、脱离的过程,研究水滴雾化机理,得到油介质静止时雾化水滴的大小与水在喷口处流速、喷口当量直径之间的关系,对模拟所得数据进行拟合得到一定范围内三者之间的关系式。对油介质流动情况下雾化水滴的大小与喷口直径、水在喷口处流速和油介质的流速之间的关系做了研究,统计雾化水滴的粒径大小,得出符合Rosin-Rammler分布的结论。对于单个水滴颗粒的内部导热相变和水滴表面与外界油介质对流换热过程,本文通过一定的简化建立数学模型,采用Visual Basic语言搭建模拟平台进行数值计算,得到水滴与油介质相对速度、水滴直径、水滴初温与油介质初温对水滴结冰时间的影响,以及水滴内部的相变界面位置的变化规律。同时,运用欧拉-拉格朗日数值模拟方法建立离散相模型以研究多个水滴同时并存于低温油介质流场中的多相流动和换热过程,用欧拉方法描述油介质流场及温度场,用拉格朗日方法对离散相水滴进行跟踪,并记录各个水滴的位置、温度及换热量,建立动量守恒方程以及能量守恒方程,并使用基于C语言的用户自定义函数编制水滴传热以及相变定律,对水滴在不同工况下的冻结状态进行研究,模拟得到水滴直径、水与油的质量流量对油介质的进出口温差的影响,以及水滴大小和油介质初温对水滴冻结率的影响。更多还原

【Abstract】 This paper studies the characteristics of water atomization in oil, which is the key problem of a new fluid ice producing technology. Numerical method is used in the research, and relevant results and conclusions are obtained.The mechanism of the new fluid ice technology is that oil with low temperature is guided into a vertical channel, and water is atomized into the oil by an atomization machine designed especially. The oil should not be dissolved in water. The water droplets are cooled in the channel flow mixed with cold oil and become ice particles, thus the problem of heat resistance increase which exists in most methods of fluid ice producing could be avoided. This is a multiphase flow and heat exchange process of water droplet, ice particles and oil. According to the experiment of the dissolving characteristics in water, the 25# transformer oil is selected as the cold-carrying medium.Based on the new method of fluid ice producing, VOF model is established to simulate water atomization in oil by Euler-Euler numerical simulation method. The oil phase and the water phase are regarded as continuum. The moving interface between oil and water is tracked. The process of water droplet forming, growing and breaking away is observed to study the mechanism of water atomization. The relations between the size of water droplets, the water velocity in spout, the oil velocity, and the diameter of spout are obtained at the given conditions that the oil is stationary or moving. The size of water droplets are in good agreement with Rosin-Rammler distribution.The mathematical model of heat conduction inside single droplet and heat convection with oil is established by Visual Basic under some simplification. The influences of relative velocity of water droplets and oil, the size of droplets and the initial temperature of oil and water on the icing time are investigated, and the disciplines of phase change position are also studied. Euler-Lagrange method is applied to set up discrete phase model whose function is to track discrete particles. The flow and temperature field of oil are simulated by Lagrange method. And the position, temperature and quantity of heat exchange are recorded to research the freezing state of droplets in different conditions. The equations of momentum conservation and energy conservation are established. The heat transfer and phase change disciplines are determined by user-defined functions using C Language. The influence of the size of water droplets and the mass flux of water and oil on the inlet and outlet oil temperature difference, and the influence of the droplet size, the initial temperature of oil on the percentage of frozen droplets are studied.更多还原