Simplified correlations for free convection from a horizontal isothermal cylinder

•Developed regime-specific correlations for free convection from an isothermal cylinder for a Pr ≈ 0.7.•Developed simplified regime-specific correlations for free convection from an isothermal cylinder for any Pr.•Proposed a combined correlation, with a blending function, that is applicable for any Ra and Pr.•The proposed simplified correlations agree well with existing literature. Heat transfer by buoyancy-driven convection from a heated horizontal cylinder is present in many situations. Applications occur in nuclear reactor safety, solar energy systems, computer cooling, and many heat exchangers. A number of experimental and numerical studies exist for such flow situations and often provide correlating equations to calculate the heat transfer. The existing studies, most of which are for the case where Prandtl number is approximately 0.7, show a considerable variation in their average Nusselt number predictions. Some studies have addressed the variation in Prandtl number with reasonably accurate and consistent correlations but these are often complex and cumbersome to use. To address these issues, the current paper proposes simplified sets of correlating equations using results from prior numerical and experimental studies.