Influence of nozzle-to-skin distance in cryogen spray cooling for dermatologic laser surgery

• Published in: Lasers in surgery and medicine Vol. 28; no. 2; pp. 113 - 120
• Main Authors: Aguilar, Guillermo, Majaron, Boris, Pope, Karl, Svaasand, Lars O., Lavernia, Enrique J., Nelson, J. Stuart
• Format: Journal Article
• Language: English
• Published: New York John Wiley & Sons, Inc 2001; Wiley-Liss
• Subjects: Biological and medical sciences; coalescence; cooling selectivity; cryogen layer; Cryotherapy - instrumentation; Cryotherapy - methods; Dermatologic Surgical Procedures; Dermatology - methods; droplet diameter; Drug Delivery Systems - instrumentation; Equipment Design; Equipment Safety; heat transfer coefficient; Hot Temperature - adverse effects; Laser Therapy - methods; Medical sciences; momentum; Sensitivity and Specificity; Skin plastic surgery; Skin Temperature - radiation effects; Surgery (general aspects). Transplantations, organ and tissue grafts. Graft diseases; temperature; velocity; Positioning; Skin disease; Dermatology; Heat distribution; Droplet; Optimization; Operating conditions; Cryogenic unit; Surgery; Laser; Spray cooling; Atomization; Heat transfer
• ISSN: 0196-8092; 1096-9101
• DOI: 10.1002/lsm.1025

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.