全球变化知识资源中心

In laser dermatology, cryogen spray cooling has been used to protect the epidermis from unwanted thermal damage. In this work, spray characteristics and surface heat transfer dynamics were simulated by two-way coupling hybrid vortex method to evaluate the surface cooling capacity of R134a, R404A and R1234yf in terms of cooling density and effective heat flux. Simulation results reveal that R404A has the largest cooling capacity and smallest dispersion. R1234yf has similar spray characteristics but smaller dispersion compared with R134a. The maximum effective heat flux for R134a, R404A and R1234yf was determined as 262.1, 407.5 and 225.8 kW/m(2) at the spray distances of 25.6, 30.8 and 25.1 mm, respectively. Substituting the environment friendly R1234yf for R134a can remarkably reduce global warming potential by over 1430 times and increase cooling density but insufficient cooling capacity. The effective heat flux of R1234yf can be enhanced by 18.8% by reducing the nozzle diameter and decreasing the back pressure (D = 0.4 mm, P-b = 0.01 MPa). This result is comparable with that of R134a under 1 atm and provides a theoretical basis for R1234yf potential application in clinics.