Characteristic scales in natural convection around an isothermal horizontal cylinder for Pr < 1 fluids

► Scale Analysis is applied to natural convection from a horizontal isothermal cylinder. ► The fluid is initially at rest and the fluid properties yield Pr < 1. ► Characteristic time, length, velocity and Nusselt scales are compared with CFD results. ► Scaling constants are close to unity, so the proposed scales are reasonably accurate.