Cryogen spray cooling: Effects of droplet size and spray density on heat removal.
OBJECTIVE
Cryogen spray cooling (CSC) is an effective method to reduce or eliminate non-specific injury to the epidermis during laser treatment of various dermatological disorders. In previous CSC investigations, fuel injectors have been used to deliver the cryogen onto the skin surface. The objective of this study was to examine cryogen atomization and heat removal characteristics of various cryogen delivery devices.


METHODS
Various cryogen delivery device types including fuel injectors, atomizers, and a device currently used in clinical settings were investigated. Cryogen mass was measured at the delivery device output orifice. Cryogen droplet size profiling for various cryogen delivery devices was estimated by optically imaging the droplets in flight. Heat removal for various cryogen delivery devices was estimated over a range of spraying distances by temperature measurements in an skin phantom used in conjunction with an inverse heat conduction model.


RESULTS
A substantial range of mass outputs were measured for the cryogen delivery devices while heat removal varied by less than a factor of two. Droplet profiling demonstrated differences in droplet size and spray density.


CONCLUSIONS
Results of this study show that variation in heat removal by different cryogen delivery devices is modest despite the relatively large difference in cryogen mass output and droplet size. A non-linear relationship between heat removal by various devices and droplet size and spray density was observed.
Department of Bioengineering, Rice University, Houston, Texas 77251, USA.
B M
BM
Pikkula
J H
JH
Torres
J W
JW
Tunnell
B
B
Anvari
D000287:Administration, Topical; D002056:Burns / Q000209:etiology / Q000517:prevention & control*; D005617:Chlorofluorocarbons, Methane / Q000008:administration & dosage; D017679:Cryotherapy / Q000379:methods*; D003880:Dermatology / Q000379:methods; D016503:Drug Delivery Systems; D004867:Equipment Design; D004869:Equipment Safety; D006358:Hot Temperature / Q000009:adverse effects*; D006801:Humans; D007431:Intraoperative Complications / Q000517:prevention & control; D053685:Laser Therapy / Q000009:adverse effects* / Q000379:methods*; D010316:Particle Size; D012034:Refrigeration / Q000379:methods; D012680:Sensitivity and Specificity; D012871:Skin Diseases / Q000601:surgery; D012881:Skin Temperature / Q000528:radiation effects
D005617:Chlorofluorocarbons, Methane