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.