title: Radial and temporal variations in surface heat transfer during cryogen spray cooling.
abstract: Cryogen spray cooling (CSC) is a heat extraction process that protects the epidermis from thermal damage during dermatologic laser surgery. The objective of the present work is to investigate radial and temporal variations in the heat transferred through the surface of a skin phantom during CSC. A fast-response thermal sensor is used to measure surface temperatures every 1 mm across a 16 mm diameter of the sprayed surface of the phantom. An analytical expression based on Fourier's law and Duhamel's theorem is used to compute surface heat fluxes from temperature measurements. Results show that radial and temporal variations of the boundary conditions have a strong influence on the homogeneity of heat extraction from the skin phantom. However, there is a subregion of uniform cooling whose size is time dependent. It is also observed that the surface heat flux undergoes a marked dynamic variation, with a maximum heat flux occurring at the centre of the sprayed surface early in the spurt followed by a quick decrease. The study shows that radial and temporal variations of boundary conditions must be taken into account and ideally controlled to guarantee uniform protection during CSC of human skin.
authors.affiliation: Department of Mechanical Engineering, University of California, Riverside, CA 92521, USA.
authors.forename: Walfre
authors.initials: W
authors.lastname: Franco
authors.forename: Jie
authors.initials: J
authors.lastname: Liu
authors.forename: Guo-Xiang
authors.initials: GX
authors.lastname: Wang
authors.forename: J Stuart
authors.initials: JS
authors.lastname: Nelson
authors.forename: Guillermo
authors.initials: G
authors.lastname: Aguilar
mesh_terms: D001831:Body Temperature / Q000187:drug effects / Q000502:physiology*; D001833:Body Temperature Regulation / Q000187:drug effects / Q000502:physiology*; D005617:Chlorofluorocarbons, Methane / Q000008:administration & dosage*; D003080:Cold Temperature; D003198:Computer Simulation; D017679:Cryotherapy / Q000379:methods*; D004735:Energy Transfer / Q000187:drug effects / Q000502:physiology; D006801:Humans; D008954:Models, Biological; D012879:Skin Physiological Phenomena / Q000187:drug effects*; D013817:Thermography / Q000379:methods
chemical_list: D005617:Chlorofluorocarbons, Methane