I am working on a problem involving heat transfer from a horizontal pipe in air. I am having trouble with it and not getting the solution I expect, and I think it is because of the convection component of the heat transfer. The general formula I am following for convection from a horizontal pipe is: Q = h*A*(Tsurface-Tambient) where: h = convection heat transfer coefficient A = pipe surface area Tsurface = surface temperature of pipe Tambient = air temperature around pipe I am using the following formulas for calculating the heat transfer coefficient: Natural Convection: h = 1.32*((Tsurface-Tambient)/D)^0.25 Forced Convection: h = C*Re^n*Pr^(1/3)*k/D where: Re = Reynolds number Pr = Prandtl number k = thermal conductivity of air D = outside pipe diameter C,n = constants dependent on Re (can't remember their name off-hand, see chart) Reynolds Number C n 0.4-4 0.989 0.330 4-40 0.911 0.385 40-4,000 0.683 0.466 4,000-40,000 0.193 0.618 40,000-400,000 0.0266 0.805 Are these formulas appropriate (natural convection in particular as this was given to me by a colleague and I have no clue where he got it)? The forced convection is from a text book (which I don't have at the moment), however the book did not specify the orientation of the pipe. If anyone could chime in, or maybe provide a link to a 'how-to' on calculating convection around pipes that would be great, thanks!