Aguilar G, Majaron B, Pope K, Svaasand L O, Lavernia E J, Nelson J S
Whitaker Center for Biomedical Engineering, University of California, Irvine, California 92697, USA.
Lasers Surg Med. 2001;28(2):113-20. doi: 10.1002/lsm.1025.
Cryogen sprays are used for cooling human skin during various laser treatments. Since characteristics of such sprays have not been completely understood, the optimal atomizing nozzle design and operating conditions for cooling human skin remain to be determined.
Two commercial cryogenic spray nozzles are characterized by imaging the sprays and the resulting areas on a substrate, as well as by measurements of the average spray droplet diameters, velocities, temperatures, and heat transfer coefficients at the cryogen-substrate interface; all as a function of distance from the nozzle tip.
Size of spray cones and sprayed areas vary with distance and nozzle. Average droplet diameter and velocity increase with distance in the vicinity of the nozzle, slowly decreasing after a certain maximum is reached. Spray temperature decreases with distance due to the extraction of latent heat of vaporization. At larger distances, temperature increases due to complete evaporation of spray droplets. These three variables combined determine the heat transfer coefficient, which may also initially increase with distance, but eventually decreases as nozzles are moved far from the target.
Sprayed areas and heat extraction efficiencies produced by current commercial nozzles may be significantly modified by varying the distance between the nozzle and the sprayed surface.
在各种激光治疗过程中，低温喷雾用于冷却人体皮肤。由于此类喷雾的特性尚未完全了解，因此用于冷却人体皮肤的最佳雾化喷嘴设计和操作条件仍有待确定。
通过对喷雾及其在基板上形成的区域进行成像，以及测量低温喷雾与基板界面处的平均喷雾液滴直径、速度、温度和传热系数，对两种商用低温喷雾喷嘴进行特性分析；所有这些均作为距喷嘴尖端距离的函数。
喷雾锥的大小和喷雾区域随距离和喷嘴而变化。在喷嘴附近，平均液滴直径和速度随距离增加，在达到某个最大值后缓慢减小。由于汽化潜热的提取，喷雾温度随距离降低。在较大距离处，由于喷雾液滴完全蒸发，温度升高。这三个变量共同决定了传热系数，传热系数最初也可能随距离增加，但随着喷嘴远离目标，最终会降低。
通过改变喷嘴与喷雾表面之间的距离，当前商用喷嘴产生的喷雾区域和热提取效率可能会显著改变。
