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Proceedings Paper

Design and construction of experimental device to study cryogen droplet deposition and heat transfer
Author(s): Matthew Keller; Guillermo Aguilar; J. Stuart Nelson
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Paper Abstract

Cryogen spray cooling (CSC) is used to pre-cool the epidermis during laser dermatological procedures such as treatment of port wine stain (PWS) birthmarks. It is known that PWS patients with medium to high epidermal melanin concentrations are at a high risk of epidermal thermal damage after laser irradiation. To avoid this complication, it is necessary to maximize CSC efficiency and, thus, essential to understand the mechanical and thermal interactions of cryogen droplets with the sprayed surface. It has been observed that cryogen sprays exhibit droplet rebound as droplets impinge on the skin surface. Studies of water droplet impact on hard surfaces have shown that droplet rebound may be suppressed by dissolving small amounts (a few percent) of diverse polymer or surfactant solutions prior to atomization. To investigate the possibility of suppressing the rebound of cryogen droplets in a similar way, we have constructed a device that allows observation of the impact, spreading, and rebound of individual water and cryogen droplets with and without these solutions, and their influence on cryogen/surface dynamics and heat transfer. Our preliminary studies show that dissolving a 4% non-ionic surfactant in water reduces droplet rebound and thickness of the residual liquid layer. The maximum spread of water droplets after impact can be described within 20% accuracy by a previously developed theoretical model. The same model provides an even more accurate prediction of the maximum spread of cryogen droplets. This study will aid the analysis of future results and design conditions of new studies, which will recreate conditions to determine if added surfactant solutions suppress droplet rebound and lead to improved CSC efficiency.

Paper Details

Date Published: 10 June 2003
PDF: 9 pages
Proc. SPIE 4954, Thermal Treatment of Tissue: Energy Delivery and Assessment II, (10 June 2003); doi: 10.1117/12.497629
Show Author Affiliations
Matthew Keller, Harvey Mudd College (United States)
Beckman Laser Institute (United States)
Guillermo Aguilar, Beckman Laser Institute/Univ. of California, Irvine (United States)
Univ. of California, Irvine (United States)
J. Stuart Nelson, Beckman Laser Institute/Univ. of California, Irvine (United States)
Univ. of California, Irvine (United States)

Published in SPIE Proceedings Vol. 4954:
Thermal Treatment of Tissue: Energy Delivery and Assessment II
Thomas P. Ryan, Editor(s)

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