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Effect of skin indentation on heat transfer during cryogen spray cooling
Author(s) -
Basinger Brooke,
Aguilar Guillermo,
Nelson J. Stuart
Publication year - 2004
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.20011
Subject(s) - indentation , materials science , heat flux , heat transfer , nozzle , composite material , spray nozzle , mechanics , mechanical engineering , physics , engineering
Background and Objectives Cryogen spray cooling (CSC) is used to pre‐cool the epidermis during dermatological laser procedures such as treatment of port wine stain (PWS) birthmarks, hair removal, and non‐ablative photorejuvenation. Thus far, heat transfer studies related to CSC optimization have assumed a flat surface but clinical observation suggests that human skin indents due to the force of an impinging cryogen spray. Study Design/Materials and Methods High‐speed videos of cryogen spray impingement on in vivo human skin were taken and the resulting indentations characterized as a function of both nozzle‐to‐skin distance and anatomic location. Detectors with pre‐formed indentations were constructed and heat flux measurements were performed at two nozzle‐to‐surface distances. Results Indentation causes cryogen accumulation that reduces the efficiency of heat transfer when compared to spray impingement on a flat surface. Large indentations, however, encourage convective flow within the cryogen pool that mitigates many of the negative effects of liquid layer thickening and improves the heat flux. Conclusions Flat surfaces produce the most efficient heat transfer, but once indentation exists (as it does in all clinically relevant cases), larger indentations produce a higher maximum heat flux. This suggests that higher momentum sprays (which produce larger skin indentations for identical spurts) than those in current clinical use may improve CSC efficiency. Lasers Surg. Med. 34:155–163, 2004. © 2004 Wiley‐Liss, Inc.