Uniform Heat Transfer of Medical Cryogen Sprays through Wire Meshes

Cryogen spray cooling (CSC) protects the epidermal layer during dermatologic laser surgery (DLS) of superficial vascular lesions. Because of spray characteristics the protection provided radially is relatively uniform only by the spray axis. The present work explores mass-deposition passive-control during CSC in order to increase the radial homogeneity of heat extraction. A stainless steel mesh is placed 5 and 10 mm away from the nozzle tip of the spray system, and a fast-response thermal sensor is used to measure temperatures across the radius of the sprayed surface of a human skin phantom. Surface measurements along with an analytical expression are used to compute heat fluxes. Lower temperatures and higher heat fluxes are obtained without the mesh. Consequently, the mesh quantitatively reduces cooling. However, radial distributions of temperature and heat flux show that more uniform heat transfer in time and space takes place using the mesh. Evolution of temperatures in time and space shows that the mesh introduces a thermal delay, which may be used to compensate for the reduction in cooling. Therefore, passive mass-deposition during CSC through a wire mesh effectively allows to establish a more uniform temporal and radial heat transfer.