单个水滴蒸发过冷过程的特性分析

Characteristic analysis of single water droplet in evaporative supercooled process

为分析单个水滴在低温、低湿空气中的运动和蒸发特性,建立了描述整个传热传质及运动过程的数学模型,并通过对悬挂水滴的蒸发冷却实验验证了该模型的有效性.通过模拟计算获得了水滴温度、直径、速度和运动轨迹的变化规律,以及水滴初始参数和空气速度对制冰效率的影响.结果表明,水滴在某一喷射角度下,直径越小,同样的下落高度水滴水平飞行的距离越短,而相应的速度衰减则越快,同时水滴蒸发过冷所需的时间越短.另外,水滴初始温度越低和逆流空气速度越高,在很短的下落高度内,水滴就实现了过冷,而水滴直径的变化量随着初始水温和空气流速的增大而增大,因此对雾化水滴进行预冷却不仅可提高系统制冰效率,还能减少水滴的蒸发损失.

To analyze the movement and evaporation characteristics of single water droplet in low temperature and low humidity ratio air,a mathematical model of water droplet heat and mass transfer and movement process was proposed.The evaporation process of droplet in supercooled stage was simulated through theoretical model,results from modeling basically tally with experiment of hanging single water droplet.The temperature,diameter,velocity and trajectory of water droplet during evaporation and motion process and the influence of the initial parameters of droplet and air velocity were investigated.The numerical results show that at a certain spray angle and with same dropping height the smaller droplet diameter can shorten movement distance at horizontal direction and the super-cooled time of water droplet,meanwhile decrease the corresponding velocity of water droplet faster.The lower initial temperature of water droplet or the higher velocity of air can improve the cooling rate of water droplet and the water droplet can be cooled to supercooled state in a very short dropping height.In addition,the higher the initial temperature of water droplet and the air velocity are,the faster the diameter of water droplet reduces.Thus,the precooled water droplets can not only improve the ice-making efficiency but also reduce the evaporative loss of water droplet.