Dynamics of cryogen deposition relative to heat extraction rate during cryogen spray cooling

Wim Verkruysse; Boris Majaron; Guillermo Aguilar; Lars Othar Svaasand; J. Stuart Nelson M.D.

doi:10.1117/12.386235

17 May 2000 Dynamics of cryogen deposition relative to heat extraction rate during cryogen spray cooling

Wim Verkruysse, Boris Majaron, Guillermo Aguilar, Lars Othar Svaasand, J. Stuart Nelson M.D.

Proceedings Volume 3907, Lasers in Surgery: Advanced Characterization, Therapeutics, and Systems X; (2000) https://doi.org/10.1117/12.386235
Event: BiOS 2000 The International Symposium on Biomedical Optics, 2000, San Jose, CA, United States

Abstract

Goal is to investigate how delivery nozzle design influences the cooling rate of cryogen spray as used in skin laser treatments. Cryogen was sprayed through nozzles that consist of metal tubes with either a narrow or wide diameter and two different lengths. Fast-flashlamp photography showed that the wide nozzles, in particular the long wide one, produced a cryogen jet (very small spray cone angle) rather than a spray (cone angles of about 15 degrees or higher) and appeared to atomize the cryogen less finely than the narrow nozzles. We measured the cooling rate by spraying some cryogen on an epoxy-block with thermocouples embedded. The heat extraction rate of the wide nozzles was higher than that of the narrow nozzles. The results suggest that finely atomized droplets produced by the narrow nozzles do not have enough kinetic energy to break through a layer of liquid cryogen accumulated on the object, which may act as a thermal barrier and, thus, slow down heat extraction. Presumably, larger droplets or non- broken jets ensure a more violent impact on this layer and therefore ensure an enhanced thermal contact. The margin of error for the heat extraction estimate is analyzed when using the epoxy-block. We introduce a complementary method for estimating heat extraction rate of cryogen sprays.

Citation Download Citation

Wim Verkruysse, Boris Majaron, Guillermo Aguilar, Lars Othar Svaasand, and J. Stuart Nelson M.D. "Dynamics of cryogen deposition relative to heat extraction rate during cryogen spray cooling", Proc. SPIE 3907, Lasers in Surgery: Advanced Characterization, Therapeutics, and Systems X, (17 May 2000); https://doi.org/10.1117/12.386235

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