Temporal and radial dependent profiles for surface heat transfer during R404a spray cooling

Cryogen spray cooling has been applied to protect epidermis from thermal damage during laser surgery. However, the presently used cryogen, R134a shows unsatisfactory efficacy in minimizing laser energy absorption by melanin in darkly pigmented human skins. Previous work of our group showed that R404a had the potential of improving cooling protection to epidermis, while there is few related research on the surface heat transfer during R404a spray cooling. This paper presents an experimental study on the temporal and radial variation in temperature and heat flux during spray cooling using R404a by a specially designed nozzle with expansion chamber, which significantly improved the atomization effect. The temporal and radial conditions strongly influenced uniformity of surface heat transfer. However, there existed a sub-region of uniform cooling with radius of 2 mm around spray center with high heat flux. The result of this experiment could provide guidance for guaranteeing uniform cooling protection during clinical laser surgery.