Insulated Pipe Transient Heat Loss
Insulated Pipe Transient Heat Loss
(OP)
Hello,
I am trying to calculate the cool down time of a stagnant fluid in an insulated pipe exposed to ambient winter conditions. I was wondering if the "lumped capacitance" method is the right approach to solve a problem like this?
The link: https://www.wbdg.org/design/midg_design.php provides the following equation to calculate the cool down time:

Where:
Theta = cooling time
RT = insulation heat transfer coefficient
The equation above looks much the same as the solution to a lumped capacitance problem, however, the convective heat transfer coefficient, H, is being replaced with the the thermal resistance of the insulation, RT. My question is whether it is appropriate to do so? The insulation itself will have a temperature gradient which will vary over time, and this equation doesn't seem to account for that (atleast that is my understanding).
If anyone can shed some light on this topic that would be great.
I am trying to calculate the cool down time of a stagnant fluid in an insulated pipe exposed to ambient winter conditions. I was wondering if the "lumped capacitance" method is the right approach to solve a problem like this?
The link: https://www.wbdg.org/design/midg_design.php provides the following equation to calculate the cool down time:

Where:
Theta = cooling time
RT = insulation heat transfer coefficient
The equation above looks much the same as the solution to a lumped capacitance problem, however, the convective heat transfer coefficient, H, is being replaced with the the thermal resistance of the insulation, RT. My question is whether it is appropriate to do so? The insulation itself will have a temperature gradient which will vary over time, and this equation doesn't seem to account for that (atleast that is my understanding).
If anyone can shed some light on this topic that would be great.





RE: Insulated Pipe Transient Heat Loss
This expression may be ok as a first approximation if it is indeed correct; it doesnt account for the heat content in the metal wall, but this may be small is relation to the heat content of the fluid in your case.
Before you dive headlong into using this equation, would suggest we check this out against a pseudo steady state approximation, by using several short time steps..
RE: Insulated Pipe Transient Heat Loss
TTFN
I can do absolutely anything. I'm an expert!
homework forum: //www.engineering.com/AskForum/aff/32.aspx
FAQ731-376: Eng-Tips.com Forum Policies forum1529: Translation Assistance for Engineers