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An analysis of heat removal during cryogen spray cooling and effects of simultaneous airflow application
Author(s) -
Torres Jorge H.,
Tunnell James W.,
Pikkula Brian M.,
Anvari Bahman
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.1077
Subject(s) - airflow , materials science , thermal conduction , heat flux , evaporation , evaporative cooler , biomedical engineering , composite material , optics , mechanics , heat transfer , thermodynamics , medicine , physics
Background and Objective Cryogen spray cooling (CSC) is a method used to protect the epidermis from non‐specific thermal injury that may occur as a result of various dermatological laser procedures. However, better understanding of cryogen deposition and skin thermal response to CSC is needed to optimize the technique. Study Design/Materials and Methods Temperature measurements and video imaging were carried out on an epoxy phantom as well as human skin during CSC with and without simultaneous application of airflow which was intended to accelerate cryogen evaporation from the substrate surface. An inverse thermal conduction model was used to estimate heat flux and total heat removed. Results Lifetime of the cryogen film deposited on the surface of skin and epoxy phantom lasted several hundred milliseconds beyond the spurt, but could be reduced to the spurt duration by application of airflow. Values over 100 J/cm 3 were estimated for volumetric heat removed from the epidermis using CSC. Conclusions “Film cooling” instead of “evaporative cooling” appears to be the dominant mode of CSC on skin. Estimated values of heat removed from the epidermis suggest that a cryogen spurt as long as 200 milliseconds is required to counteract heat generated by high laser fluences (e.g., in treatment of port wine stains) in patients with high concentration of epidermal melanin. Additional cooling beyond spurt termination can be avoided by simultaneous application of airflow, although it is unclear at the moment if avoiding the additional cooling would be beneficial in the actual clinical situation. Lasers Surg. Med. 39:477–486, 2001. © 2001 Wiley‐Liss, Inc.