Heat transfer coefficient
Heat transfer coefficient
(OP)
Hello all,
I have a questions, can be possible a heat transfer coefficient of 6 (W/m^2/K) between the air inside an office an a pipe of Polyurethane? I assumed natural flow convection. I have calculated the heat flow in a radial direction (everything is known: temperatures, thermal conductivity...) and with a normal parameter of the heat transfer coefficient (15 W/m^2/K)the calculation doesn't have sense.
Thank you in advance.
Cheers
I have a questions, can be possible a heat transfer coefficient of 6 (W/m^2/K) between the air inside an office an a pipe of Polyurethane? I assumed natural flow convection. I have calculated the heat flow in a radial direction (everything is known: temperatures, thermal conductivity...) and with a normal parameter of the heat transfer coefficient (15 W/m^2/K)the calculation doesn't have sense.
Thank you in advance.
Cheers





RE: Heat transfer coefficient
For a horizontal pipe and natural convection (you might want to consider radiative heat transfer too):
Nu={ 0.60 + (0.387Ra^(1/6))/[1+(0.559/Pr)^(9/16)]^(8/27) }^2
Where:
Nu = Nusselt number
Ra = Rayleigh number
Pr = Prandtl number
All the above numbers calculated using air properties evaluated at film temperature. Please note that the pipe external wall temperature could be (probably is) a bit different from that of the fluid flowing inside.
RE: Heat transfer coefficient
The problem to calculate an accurate value of it is that the pipe it's not completely horizontal or vertical, also in some points it's touching some platforms...really difficult to be accurate.
Thank you for the info again!
Cheers
RE: Heat transfer coefficient
TTFN
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RE: Heat transfer coefficient
I don't know if it's clear enough, sorry.
Thanks, cheers.
RE: Heat transfer coefficient
TTFN
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RE: Heat transfer coefficient
If you have to deal with natural convection and inclined cylinders, you can look on the web for "Raithby and Hollands". They do have developed a correlation for the scenario above mentioned which seems to work quite well.
RE: Heat transfer coefficient
@ione, thank you very much! I will check right now.
Thank you both.
Cheers.
RE: Heat transfer coefficient
Thanks
RE: Heat transfer coefficient
Nu={ 0.772 + [0.228/(1 + 0.676*(2*L*cot(alpha)/D)^1.23]}*[cos(alpha) + D*sin(alpha)/L]^0.25*Ra^0.25
Valid for L/D>5
Where:
L = length
D = diameter
alpha = angle between the axis of the cylinder and the horizontal
Nu = Nusselt number
Ra = Rayleigh number
RE: Heat transfer coefficient
RE: Heat transfer coefficient
TTFN
FAQ731-376: Eng-Tips.com Forum Policies
RE: Heat transfer coefficient
Thank you
Cheers.