Spray cooling is widely used in industry. Complicated surface heat transfer characteristics are needed to reveal the mechanism. In this work

the surface heat transfer experiments of cryogen spray cooling (CSC) with R134a

R407C and R404A were conducted. The spray Biot number was defined to represent the ratio between the internal thermal resistance of substrate and the resistance of surface convective heat transfer. Dimensionless Reynolds number Rel and Fourier number Fol were proposed to represent the maximum heat flux and the corresponding time

respectively. By coupling Jakob number with Rel number and droplet Weber number (We)

dimensionless correlations of maximum heat flux and the corresponding time were constructed. The similarity of the transient spray cooling process with different cryogens was found and the dimensionless correlation of time-dependent heat flux was obtained. By using these correlations

the simulated transient surface temperature during cryogen spray cooling agreed well with the experiment data

which proved the accuracy of the correlations.