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Influence of nozzle‐to‐skin distance in cryogen spray cooling for dermatologic laser surgery
Author(s) -
Aguilar Guillermo,
Majaron Boris,
Pope Karl,
Svaasand Lars O.,
Lavernia Enrique J.,
Nelson J. Stuart
Publication year - 2001
Publication title -
lasers in surgery and medicine
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.888
H-Index - 112
eISSN - 1096-9101
pISSN - 0196-8092
DOI - 10.1002/lsm.1025
Subject(s) - nozzle , spray nozzle , materials science , evaporation , spray characteristics , vaporization , heat transfer , heat transfer coefficient , substrate (aquarium) , mechanics , composite material , optics , chemistry , thermodynamics , physics , organic chemistry , geology , oceanography
Background and Objective 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. Materials and Methods 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. Results 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. Conclusions 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. Lasers Surg. Med. 28:113–120, 2001. © 2001 Wiley‐Liss, Inc.