I'm at little rusty on my heat transfer and could use some help. I'm trying to calculate the approximate time to freeze standing water in a 18inch steel pipe. I have some parameters and made some assumptions and they are: The pipe is 18inch carbon steel The standing water is initially around 68oF The outside temp is around 0oF There is a constant breeze around 5mph No insulation around pipe The pipe is exsposed to the air and not buried The pipe is completely filled with water I've calculated this two different ways and came up with two completely different time values. One was around 8.7hrs and the other was around 4.8hrs. For the first method, I calculated the surface heat transfer coefficient (h) at the wind/pipe interface by: First calculating the Reynolds number (Re) of the wind/pipe interface from Re=VD/v(kinematic viscosity of air) Then I found the Prandtl number (Pr) for air at 0oF Then I calculated the Nusselt number (Nu) by Nu=0.023 x (Re)4/3 x (Pr)1/3 Then I found the thermal conductivity of the air kf Then I calculated the surface heat transfer coefficient(h) by h=(Nu x kf)/Dpipe I came up with h~11 W/(m2 K) Once I found the surface heat transfer coefficient, I calculated the Biot number (Bi) by Bi=hD/ks , where ks is the thermal conductivity of the carbon steel pipe. I found Bi=0.003364666 , and with Bi<0.1 I figured could use the lumped capacitance method. Note: density=rho=p ps=density of steel pw=density of water cs=heat capacitance of steel cw=heat capacitance of water Ti=initial water temp Tinf=air temp T=water at 32oF or 273.15 K Using the lumped capacitance method, time (t) in secs can be found from t=[(pVc)tot/(hAs)]*ln[(Ti-Tinf)/(T-Tinf)] Where (pVc)tot=[((pscs(Do-Di))/4)s+((pwcw(Di))/4)w] and so ((pVc)tot)*(1/h)*ln[(Ti-Tinf)/(T-Tinf)]=t This method is how I came up with 8.7hrs. I came up with 4.8hrs using a method out of an ASHRAE handbook. Is the method okay for a good approximation? Is 8.7hrs a good approximation? If there's something I'm doing wrong or a better approach, please let me know. Thanks for the help.