2015 12 Heat-loss-from-Insulated-pipe
2015 12 Heat-loss-from-Insulated-pipe
2015 12 Heat-loss-from-Insulated-pipe
CHE GUIDE
C h e m i c a l E n g i n e e r ' s G u i d e (https://cheguide.com/)
MasterLife CI 220
(https://cheguide.com/2015/12/heat-loss-from-insulated-pipe/)
Heat loss/gain takes place from a pipe carrying hotter/ colder fluid than ambient temperature. Insulation
reduces the heat loss to surroundings. Heat loss depends upon number of factors like insulation
thickness, ambient temperature, wind speed etc. This article shows how to calculate heat loss from an
insulated pipe and a bare pipe to surroundings.
Example
A 3 Carbon steel pipe is carrying hot oil at 180C and insulated with 50 mm thick calcium silicate insulation.
Insulation is cladded with a sheet with surface emissivity of 0.9. Ambient temperature is 28C and wind
velocity is 3.5 m/s. Calculate surface temperature and heat loss from insulated and bare pipe.
where, kPIPE, kINSULATION are thermal conductivity of pipe and insulation. hin is heat transfer coefficient for
fluid flowing in pipe and hair is heat transfer coefficient due to air flowing outside the pipe. The first two
terms of denominator in above equation are generally smaller compared to remaining terms and can be
neglected. For this example first term due to pipe fluid is ignored.
https://cheguide.com/2015/12/heat-loss-from-insulated-pipe/ 29-05-2017
Heat Loss from Insulated Pipe ChE Guide Page 2 of 7
Estimate thermodynamic properties of air like thermal conductivity (k), viscosity (), expansion coefficient
( = 1/t_average), air density (), kinematic viscosity (), specific heat (Cp) and thermal diffusivity () at
average air film temperature. These properties are available in literature in form of tables, these can be
fitted into a polynomial form using excels LINEST function. Reynoldss number (Re), Prandtl number (Pr)
and Rayleigh number (Ra) are calculated based on above properties.
h_radiation
Heat transfer coefficient due to radiation is calculated using following relation.
h_convection
Convective heat transfer coefficient comprises of forced and free convection. Forced convection can be
modeled based on correlation by Churchill and Bernstein.
h_forced = Nu.k_air / D3
h_free = Nu.k_air / D3
Combined heat transfer coefficient due to forced and free convection is calculated using following
relation.
h_convection = Nu_combined.k_air / D3
Q = (t_operating t_ambient)/r_overall
https://cheguide.com/2015/12/heat-loss-from-insulated-pipe/ 29-05-2017
Heat Loss from Insulated Pipe ChE Guide Page 3 of 7
Above steps are repeated with these new estimates till there is negligible difference in temperature.
HeatLoss = D3 Q
Bare Pipe
For heat loss from bare pipe all above steps are repeated with resistance due to insulation not considered.
For this example surface temperature and heat loss are as following.
0 (https://twitter.com/sh
are)
Hidrotete says:
CheGuide says:
https://cheguide.com/2015/12/heat-loss-from-insulated-pipe/ 29-05-2017
Heat Loss from Insulated Pipe ChE Guide Page 4 of 7
thank you.
Tom
CheGuide says:
Regards
Tom
JUNG says:
CheGuide says:
Xiaoqi says:
Thank you
CheGuide says:
https://cheguide.com/2015/12/heat-loss-from-insulated-pipe/ 29-05-2017
Heat Loss from Insulated Pipe ChE Guide Page 5 of 7
Xiaoqi says:
If is emissivity for cladded surface.Then I think the equation should be like this:
In this equation, we calculate the radiation heat transferring between cladding surface and the
ambient.
Thanks
CheGuide says:
CheGuide says:
CheGuide says:
CheGuide says:
https://cheguide.com/2015/12/heat-loss-from-insulated-pipe/ 29-05-2017
Heat Loss from Insulated Pipe ChE Guide Page 6 of 7
CheGuide says:
Humberto says:
Heat Losses differ a little bit from the Website counterpart.Is it due to the Wind Speed? If so, is
there a standard wind speed you use for the website calcs?
Thanks!
https://cheguide.com/2015/12/heat-loss-from-insulated-pipe/ 29-05-2017
Heat Loss from Insulated Pipe ChE Guide Page 7 of 7
A says:
Andrew says:
CheGuide says:
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