3 replies to this topic

[rajubhai55]

Hi,

 

I currently have a problem related to heat exchange (which I do not deal with it on daily basis). We have a steel pipe through which hot gas flows. The pipe does not have any insulation. The outside air can be considered as stagnant at 25 deg C. Initially I applied the equation mentioned in following thread. But it gave me unreasonably high heat loss.

 

http://www.cheresour...insulated-pipe/

 

So I searched more and found that I may need to use "Overall heat transfer coefficient" and at this point I got confused. Can somebody provide me calculation steps(or equations) and coefficient values in my case? Do I have to use convection heat coefficient on either side of pipe material?

 

Below are details:

 

• Hot air flowing through a steel pipe.
• Hot air temp = 420 C
• Pipe Dia = 127mm
• Pipe wall thickness = 1.5 mm
• Pipe Length = 42 inches (1066mm)
• Pipe Material = steel(carbon steel)
• Outside air temp = 25 C
• Outside air = stagnant

Any help would be appreciated.

 

Thanks

 

 

[PingPong]

I suggest you first read this topic:

http://www.cheresour...tion#entry87742

 

In your case radiation loss from the very hot pipe to ambient will play a big role in the heat loss calculation. This radiant heat loss depends very much on the emissivity (emission coeffient) of the outer pipewall, which may be difficult (almost impossible) to estimate.

 

Just for my curiousity: why is this very hot pipe not insulated?

[latexman]

If nothing else, it should be insulated to protect personnel where it is possible to touch the pipe.

[Bobby Strain]

So, is there some problem with this hot pipe? If not, why bother?

 

Bobby