Abstract Cryogen spray cooling (CSC) is commonly applied in laser dermatology to protect the epidermis from thermal damage. Many efforts have attempted to improve the cooling capacity of CSC, among which the use of expansion-chambered nozzles is an effectively simple method with considerable potential. This study examined the influences of the expansion-chambered nozzle structure, including the ratios of inlet nozzle diameter to discharge nozzle diameter and of chamber diameter to discharge nozzle diameter on R134a and R404A spray cooling. Fifteen transparent expansion-chambered nozzles with the expansion chamber aspect ratio of 1.0, chamber diameter to discharge nozzle diameter ratios of 5.0–10.0, and inlet nozzle diameter to discharge nozzle diameter ratios of 0.6–1.4 were tested. The internal flow pattern inside the expansion chamber, external spray pattern, and surface heat transfer characteristics of cryogen spray using different nozzles, including the straight-tube nozzle, were investigated. The structure of the expansion chamber was found to have an important effect on the spray patterns and cooling characteristics. The spray radius obviously decreased when the expansion-chambered nozzles were used, and the spray pattern became narrower as the ratio of chamber diameter to discharge nozzle diameter increased. By contrast, the increase in ratio of two nozzle diameters enlarged the spray radius. Surface temperature and heat flux with different nozzles and cryogens showed a similarity, and correlations of surface temperature and heat flux were proposed. The introduction of expansion-chambered nozzles could effectively improve the spray cooling capacity. The minimum average surface temperature during the fully developed spray period could be reached for both R134a spray and R404A spray by an expansion-chambered nozzle with a chamber diameter to discharge nozzle diameter ratio of roughly 5.0 and an inlet nozzle diameter to discharge nozzle diameter ratio of roughly 0.6.

中文翻译：

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膨胀室喷嘴制冷剂喷雾冷却的雾化和表面传热特性

摘要 冷冻喷雾冷却 (CSC) 常用于激光皮肤病学，以保护表皮免受热损伤。许多努力试图提高 CSC 的冷却能力，其中使用膨胀室喷嘴是一种有效简单的方法，具有相当大的潜力。本研究考察了膨胀室喷嘴结构对 R134a 和 R404A 喷雾冷却的影响，包括入口喷嘴直径与排放喷嘴直径的比率以及腔室直径与排放喷嘴直径的比率。测试了 15 个透明膨胀室喷嘴，其膨胀室纵横比为 1.0，室径与排放喷嘴直径之比为 5.0-10.0，入口喷嘴直径与排放喷嘴直径之比为 0.6-1.4。膨胀室内的内部流动模式，研究了使用不同喷嘴（包括直管喷嘴）的外部喷雾模式和冷却剂喷雾的表面传热特性。发现膨胀室的结构对喷雾模式和冷却特性有重要影响。使用膨胀室喷嘴时，喷雾半径明显减小，并且随着室径与喷嘴直径之比的增加，喷雾形状变窄。相比之下，两个喷嘴直径之比的增加扩大了喷雾半径。不同喷嘴和冷冻剂的表面温度和热通量表现出相似性，并提出了表面温度和热通量的相关性。膨胀室喷嘴的引入可以有效提高喷雾冷却能力。