) is a critical first step to determine if the flow is laminar or turbulent, which then dictates the choice of Nusselt number ) correlation. : Problems where the surface temperature ( cap T sub s
Horizontal Plates: Distinct correlations for "upper surface hot" vs. "lower surface hot." Horizontal Cylinders/Spheres: Uses characteristic length
This dimensionless number represents the ratio of buoyancy forces to viscous forces, similar to how the Reynolds number works for forced convection. Rayleigh Number (
Common Mistake Caught by the Manual: Using the correlation for a vertical plate on a horizontal plate (which has a different characteristic length (L_c) and different constants).
I know many of you are working through Chapter 9 (Natural Convection) of Heat and Mass Transfer: Fundamentals and Applications, 5th Edition, by Yunus Cengel and Afshin Ghajar.