I am trying to calculate the natural convection heat transfer coefficient for a PCB with several components on it, including TPS7A8400ARGRR. I have been referencing document SNVA419C. Looking at Table 2, the calculations are gone through to estimate h. However, the h value calculated (14.39) is different than what is described in text above Table 2. Additionally, I was wondering why the Nusselt Equation was calculated for 2 surfaces of a horizontal plate? Is this to account for heat transfer on both sides of the PCB? It seems like the Grashof number was miscalculated because the volume expansivity was left out of the formula.