Experimental investigation and heat transfer correlation development for spray cooling over large horizontal cylinders in the post-Leidenfrost regime

Spray cooling is an effective method for achieving rapid heat removal in high-temperature applications such as metal quenching, nuclear reactor safety systems, and electronic thermal management. In this study, transient spray cooling experiments were conducted on a large-diameter horizontal cylinder to analyze heat transfer behavior above the Leidenfrost temperature. The surface temperature during quenching was recorded at high frequency and used to determine the local heat transfer coefficient using an energy balance approach. Experiments were performed for different nozzle-to-surface distance ratios (Z/D), and empirical correlations were developed through regression analysis. The results showed that the heat transfer coefficient strongly depends on Z/D but exhibits minimal variation in the temperature exponent. The proposed correlation accurately predicts heat transfer coefficients within ±25 % of experimental data. The developed correlation extends the applicability to large horizontal surfaces under transient spray cooling conditions, offering practical relevance for industrial quenching and thermal management systems.