喷雾冻结中液滴的换热研究  

Study on heat transfer of droplets in spray freezing

作　　者：刘阳 田丽亭[1] 王士存 刘联胜[1] Liu Yang;Tian Liting;Wang Shicun;Liu Liansheng(School of Energy and Environmental Engineering,Hebei University of Technology,Tianjin 300401,China)

机构地区：[1]河北工业大学能源与环境工程学院,天津300401

出　　处：《低温与超导》2021年第2期70-77,共8页Cryogenics and Superconductivity

基　　金：河北省自然科学基金(E2019202184);河北省重点研发计划项目(19274502D)资助。

摘　　要：以单个雾化液滴为研究对象,建立了液滴冻结传热过程以及运动过程的数学模型并验证了模型的可靠性,分析了顺逆两种风向下竖直喷射不同直径液滴的完全固化时间、质量损失率、总换热量以及冻结行程的变化规律,对比了倾斜喷射的液滴的运动情况。结果表明:液滴的完全固化时间和总换热量均随直径的增大而增大;液滴的质量损失率为3%左右,且随着直径的增大而降低;通过对流、传质和辐射的换热量占比不随直径变化,分别为92%、7%和1%;直径一定时,风速对液滴的完全固化时间、质量损失率、总换热量影响很小;顺逆风向的不同虽对液滴的完全固化时间影响很小,但对冻结行程的影响非常明显;喷射角小于20°的喷雾冻结,顺流风速小于2 m/s时,对D_(d)≤200μm的液滴而言,喷雾室横向尺寸不小于0.76 m可保证液滴冻结完成时不发生横向碰壁;逆流风速大于1 m/s时,对200μm<D_(d)≤1 mm的液滴而言,喷雾室横向尺寸不小于1.5 m可保证液滴冻结完成时不发生横向碰壁。Taking a single droplet as the research object, a mathematical model of the freezing and the movement process was established and the reliability was verified. The total solidification time, mass loss rate, total heat transfer and solidification displacement of the droplets sprayed vertically in the concurrent or counter wind were obtained and the motions of the obliquely ejected droplets were compared. The results show that the total solidification time and total heat transfer increase with the increase of the diameter;the mass loss rate is about 3%, and decreases as the increase of the diameter. The proportions of heat transfer through convection, mass transfer and radiation are respectively 92%, 7% and 1%, and do not change with diameter. When the diameter is fixed, wind speed has little effect on the total solidification time, mass loss rate and total heat transfer. Although the difference of the wind direction has little effect on the total solidification time, the effect on the solidification displacement is particularly obvious. In order to prevent the droplets from hitting the wall sideways, for spray freezing with a spray angle of less than 20°, the horizontal size of the spray chamber is not less than 0.76 m for droplets with D_(d)≤200 μm under the concurrent wind,which speed is less than 2 m/s;the horizontal size of the spray chamber is not less than 1.5 m for droplets with 200 μm<D_(d)≤1 mm under the counter wind, which speed is greater than 1 m/s.

关 键 词：单液滴 顺逆流 完全固化时间 固化位移 横向位移 

分 类 号：TK02[动力工程及工程热物理]