Passive mass deposition control of cryogen sprays through the use of wire meshes.

Abstract

Cryogen spray cooling (CSC) is used for epidermal protection during laser dermatologic surgery. However, further research is necessary to optimize the use of CSC for many applications, particularly in patients with darker skin types, and in procedures with deep-targeted chromophores. With the objective to enhance cryogen spray atomization and introduce a passive mass deposition control, stainless steel wire meshes of various sizes were positioned in the spray path of two nozzles of different diameters (0.7 and 1.4 mm). A temperature sensor placed at a fixed distance below the nozzle tips measured variations in temperature as a function of time. Calculations for heat flux (q), and overall heat extraction (Q) were done through an inverse heat conduction problem (IHCP) algorithm. The use of wire meshes reduced maximum q and thus cooling efficiency for both nozzles. However, for the larger diameter nozzle (1.4 mm), cooling duration was prolonged significantly when compared to the case without mesh, which led to an increase in Q. Wire meshes, within the range of wire diameters used, are not desirable for use with the smaller diameter nozzle because they reduce cooling efficiency. For the larger diameter nozzle, however, the prolonged cooling duration and increase in Q may be beneficial for laser dermatological procedures directed towards deeper targeted chromophores, such as hair removal.