低温球形颗粒表面喷雾冷冻涂覆液膜的生长规律

Liquid Film Growth of Spray-freezing Coating on Low Temperature Spherical Particles

对雾化液滴群在低温(-20℃)载体颗粒表面涂覆冻结过程开展了相关实验工作,研究载体颗粒直径、雾化料液流量、喷液量等参数对雾化液滴群的涂覆过程的影响,通过高清相机及图像处理分析得出颗粒涂覆投影面积,进而计算出涂覆量,得出液滴群涂覆载体颗粒的多参数数学方程,预测颗粒表面涂覆量和涂覆厚度的变化趋势,为控制涂覆过程提供理论支持.实验结果表明:颗粒直径减小,颗粒涂覆量不变,涂覆投影面积增大,小颗粒易于液滴的涂覆铺展;喷液流量增大时,颗粒涂覆量不变,颗粒涂覆投影面积增大,表明液滴初始动能大时,涂覆铺展较大,利于颗粒涂覆完成.根据涂覆料液体积恒定方程得出颗粒涂覆完全临界涂覆量及涂覆厚度,涂覆厚度约为140~180μm,且大颗粒涂覆厚度大于小颗粒.实验测得的颗粒涂覆厚度与理论预测值十分相近,且误差为±1μm,证明理论模型预测较为准确,较好地实现了喷雾冷冻低温球形颗粒表面液膜涂覆厚度的检测与控制.

Experiments about the freezing process of spray droplets coating on the surface of carrier particles at low temperature(-20℃)were carried out.The effects of operation parameters such as the carrier particle diameter,the spray volume and flow rate of the spray liquid on the coating process of spray droplets were studied.The projection area and amount of spray droplets coating were obtained with a high definition camera and image processing,and a multi-parameter equation of spray droplets coating carrier particles was obtained,which can predict the variation trend of the coating amount and thickness on the particles,so as to provide some theoretical support for a controllable coating process.The results show that when the particle diameter decreases and the coating quantity remains unchanged,the coating projection area increases and the small particles are easy for the coating to spread.When the spray flow rate increases and the coating quantity remains unchanged,the coating projection area increases,which indicates that the coating spread is larger and conducive for the completion of particle coating when the initial kinetic energy of the droplet is large.With constant volume analysis of the coating liquid and orthogonal experiment,the critical coating amount and thickness are obtained.The coating thickness is about 140-180μm,and the coating on large particles is thicker than that on small particles.The thickness of the coating measured in the experiment is very close to that predicted with the equation and the error is only±1μm,which shows that the theoretical model is quite accurate and can,to some extent,help realize the detection and control of the spray freezing coating thickness of liquid film on low temperature spherical particles.