Spray cooling is critical in many industrial applications to extract large heat fluxes from metal parts, such as hypervapotron in nuclear fusion reactors, heat treatment of steel plates in run-out table (ROT), electronic parts, and many more. The objective of the present study is to enhance the heat dissipation in transition and nucleate boiling regimes using an air-atomized water spray with water-based copper nanofluid as a coolant. The nanoparticle used in this study is energetic metal Cu, which has been prepared by mechanical milling (MM) process. The nanofluid has been prepared by suspending 0.1 vol. % Cu nanoparticles in water, with or without a dispersing agent (surfactant). The effect of type of dispersing agent on augmentation of boiling heat transfer has also been studied. The spray cooling experiments are conducted on a 6 mm thick stainless steel plate of initial temperature above 900 °C. The transient surface heat flux and temperatures are estimated using commercial inverse heat conduction software named intemp. The experimental results illustrated that transition and nucleate boiling heat flux as well as critical heat flux (CHF) increased significantly using nanofluid spray. A maximum ultrafast cooling (UFC) rate of 267 °C/s is achieved using surfactant-based nanofluid spray, which is 31.53% and 59.88% higher as compared to the nanofluid without any dispersant and pure water sprays, respectively. Overall, the surfactant-based copper nanofluid spray can serve as a better coolant on the ROT of steel processing industry.