1 Copyright © 2000 by ASME Proceedings of IMECE 2000: The International Mechanical Engineering Congress and Exposition November 5-10, 2000, Orlando, Florida CHARACTERIZATION OF CRYOGENIC SPRAY NOZZLES WITH APPLICATION TO SKIN COOLING Guillermo Aguilar 1,* , Boris Majaron 2,4 , Wim Verkruysse 2 , J. Stuart Nelson 2 , and Enrique J. Lavernia 3 1 Whitaker Center for Biomedical Engineering University of California, Irvine Irvine, CA 92697 2 Beckman Laser Institute and Medical Clinic University of California, Irvine Irvine, CA 92612 3 Department of Chemical and Biochemical Engineering and Materials Sciences University of California, Irvine Irvine, CA 92697 4 Jozef Stefan Institute Jamova 39, SI-1000 Ljubljana Slovenia * Corresponding author: Beckman Laser Institute and Medical Clinic, University of California Irvine, Irvine, CA 92612. e-mail: gaguilar@bli.uci.edu 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. NOMENCLATURE c specific heat at constant pressure [J/kg K] D droplet diameter [μm] k thermal conductivity [W/m K] L latent heat of vaporization [J/kg] m mass [mg] Nu Nusselt number Pr Prandtl number Re Reynolds number T average temperature [ o C or K] V bulk or average velocity [m/s] z distance from the nozzle [mm] Greek ρ density [Kg/m 3 ] λ’ evaporation constant [m 2 /s] Subscripts a air d relative to the droplet g relative to the air-cryogen vapor mixture l liquid s relative to the surface ∞ relative to ambient 0 initial 1 relative to time t 1 1. INTRODUCTION The use of sprays and other physical dispersions of droplets or small particles is important for many processes and engineering applications, such as in agricultural chemicals, application of paints, drying of wet solids, cooling of nuclear cores, dispersing liquid fuels for combustion, etc. Despite the fact that several studies have been carried out on liquid sprays [1-3], as well as on liquid fuel sprays [4,5], limited information exists on the thermodynamics of cryogenic