Little knowledge exists concerning the atomization mechanisms and dispersion of flashing sprays in dermatologic cooling. This study examines flashing of a high superheat fluid flowing through micro tube nozzles resembling current medical devices. A one-dimensional, semi-empirical model of refrigerant flow through capillary tubes is used to quantify internal flow characteristics. These results provide nozzle exit conditions that are then correlated to external spray characteristics determined experimentally. One-dimensional expressions for external vapor/liquid interaction are developed to determine evolution of droplet size distribution and explain measured droplet accelerations near the nozzle exit. Droplet drag coefficients are subsequently calculated and compared to existing literature. (C) 2008 Elsevier Ltd. All rights reserved.