Cryogen transient flashing spray cooling: state of art

With the rapid development of laser dermatology, the epidermis cooling technology becomes more and more important, and it is of great potential for commercial application. Cryogen spray cooling (CSC) with several tens of milliseconds has been successfully applied in laser treatment of vascular diseases, which can protect epidermis from the thermal injuries due to the absorption of melanin and hence increase the incident laser energy, leading to the improvement in therapeutic outcomes. CSC involves flashing atomization and boiling heat transfer on cooling surface. The majority of previous studies were conducted experimentally. The research progresses of the mechanism of flashing atomization, spray characteristics, heat transfer dynamics and the enhancement were summarized for the past 20 years. The typical research methods and results were compared and analyzed, and the different factors to influence the heat transfer dynamics of CSC were investigated. New spray techniques, such as using lower point cryogens and hypobaric pressure method, are effective to enhance cooling capacity. Finally, the remaining difficulties in this field were clarified and the potentials of the ongoing research were pointed out.