单液滴撞击冷表面的模拟研究
发布时间：2018-11-22 07:38
【摘要】：喷雾冷冻干燥(SFD)过程中存在雾化液滴在设备壁面的冷冻沉积问题,不仅造成产品收集率的下降,且会对产品造成二次污染,影响设备的传热传质速率,而对单液滴撞击冷板面的研究有助于解决这一问题。本文在前期单液滴撞击冷板面的实验基础上,以单个蒸馏水及普鲁兰多糖液滴为研究对象,使用数值模拟的方法研究了直径为3.2 mm的单液滴与冷板面(小于0℃)撞击铺展和固化过程,分析了撞击高度(H=100mm、250 mm、500 mm)和板面温度(T=253 K和268 K)以及板面倾角(α=0。、30。、45。和60。)对撞击过程的影响以及液滴在冷板面上冻结过程。对液滴在冷板面上的铺展和冻结过程进行了理论分析,建立了描述液滴铺展过程及在冷板面上固化的数学模型,建立了液滴铺展的二维与三维物理模型,将水平集方法和固化模型相结合,使用基于温度的热传导方程代替原有的焓值方程,并且在热容源项中加入熔化潜热,利用COMSOL Multiphysics 4.2(?)软件,耦合“两相流水平集”与“流体传热”两个物理场,求解了存在相变的传热问题。结果表明,撞击高度与板面温度对液滴在水平冷板面的铺展过程起到重要作用,撞击倾斜板面时,板面的倾角也会影响液滴在冷板面上冷冻沉积的发生,随着撞击速度和倾斜角度的增加,板面温度对液滴撞击动力学行为的影响逐渐变小,减小了液滴沉积的可能。物料的性质,如黏度等也会对液滴的冷冻沉积发生重大影响,对于较高黏度物料,温度并不起决定作用,黏度会影响液滴的铺展速率及铺展直径,且影响趋势较为明显。本文采用的模拟模型和实验的结果吻合较好,反映了液滴铺展冻结过程中的温度变化与固化情况,有利于对液滴发生冻结的状况进行直观解释。
[Abstract]:In the process of spray freeze-drying (SFD), there exists the problem of freezing deposition of atomized droplets on the wall of the equipment, which not only leads to the decrease of product collection rate, but also causes secondary pollution to the product and affects the heat and mass transfer rate of the equipment. The research of single droplet impingement on the surface of cold plate is helpful to solve this problem. On the basis of the previous experiments of single droplet impinging on the surface of cold plate, single distilled water and pullulan polysaccharide droplet were taken as the object of study. Numerical simulation was used to study the impact spread and solidification process of a single droplet with a diameter of 3.2 mm with a cold plate surface (less than 0 鈩，
本文编号：2348533
[Abstract]:In the process of spray freeze-drying (SFD), there exists the problem of freezing deposition of atomized droplets on the wall of the equipment, which not only leads to the decrease of product collection rate, but also causes secondary pollution to the product and affects the heat and mass transfer rate of the equipment. The research of single droplet impingement on the surface of cold plate is helpful to solve this problem. On the basis of the previous experiments of single droplet impinging on the surface of cold plate, single distilled water and pullulan polysaccharide droplet were taken as the object of study. Numerical simulation was used to study the impact spread and solidification process of a single droplet with a diameter of 3.2 mm with a cold plate surface (less than 0 鈩，
本文编号：2348533
本文链接：https://www.wllwen.com/kejilunwen/huaxuehuagong/2348533.html
