Correlation for heat transfer by natural convection from a horizontal pipe to atmosphere is; Nu = 0.53Gr^0.25Pr^0.25 Nu = hd / k Where, Gr = d(Ts-Tf)g / And Pr = Cp / k Show that the above correlation can be simplified to; h 1.34 (Ts-Tf / d)^0.25 =3.077 x 10^-3 =1.086 Cp=1.0063 k=2.816 x 10^-5 =1.962 x 10^-5

Reference https://www.physicsforums.com/threads/heat-transfer-and-combustion-correlations.776232/