Characterization of Cryogenic Spray Nozzles with Application to Skin Cooling

* Corresponding author: Beckman Laser Institute and Medical Clinic, University of California Irvine, Irvine, CA 92612. e-mail: [email protected] ABSTRACT Cryogenic sprays are used for cooling of human skin during laser treatments of hypervascular lesions, such as Port Wine Stain birthmarks. In this work, six straight-tube nozzles, including two commercial nozzles, are characterized by obtaining photographs of cryogenic spray shapes, as well as measurements of the average droplet diameter, velocity and temperature. An evaporation model is used to predict the evolutions of average droplet diameter and temperature. The results show two distinct spray patterns—jet-like sprays for wide nozzle diameters, and cone-like sprays for narrow nozzle diameters. The wide nozzles show significantly larger droplet diameters, larger velocities and higher temperatures, as all these variables are measured as a function of distance from the nozzle. These results complement and support previously reported results, where it was shown that wide nozzles are capable of producing larger heat transfer coefficients than those obtained with narrow nozzles.