Hot pipe and radiation heat transfer. Need help.

[jasno999]

Ok so here is my problem. I have several pipes that are carying very hot compressed gas. Some of these pipes will be running near areas that are constructed of aluminum.

I want to make sure that I do not overheat the aluminum but before I go puttign a ton of inssulation on the pipe I woudl liek to figure out how the aluminium will be affected by the hot pipe.

Let's assume there is a small air gap between the pipe and the aluminum (say 3/4 of an inch to 1.5 inches).

Say the temperature of my pipe is 600F and the temperature of the aluminum is 120F - what exuations do I use and how do I figure out how how the aluminum will get from a pipe that is 3/4" away and then fro ma pipe that is 1.5" away and so forth????

 

[IRstuff]

This is covered in most heat transfer textbooks, a free one can be downloaded here:

http://web.mit.edu/lienhard/

http://www/ahtt.html

TTFN

FAQ731-376

 

[imok2]

I get Convective Heat Transfer worst case for 3/4"= 27KW/sq meter and for 1.5"= 10.8KW/ sq meter

 

[jasno999]

Ok I will look at the textbook but I had a hard time trying to follow the equations and methodology in the last book I went thru.

I was hoping somebody could break it down for me so I could understand the process. For example imok2 how did you come up with those heat transfer values and what do they mean in terms of temperatures...

I may have asked the question wrong. Basically I want to find out how much the aluminum, that is startign out at 120F, is goign to heat up due to radiation from the hot pipe that is at 600F.... I want to make sure the aluminum does not get too hot but I am not sure how to put the equations together to figure this out.

 

[IRstuff]

You haven't really given enough information to even hazard a reasonable guess.

What's the air environment, is there air flow or strictly from convection?

How much aluminum is there, both area and mass?

Is the aluminum floating thermally or attached to something cold?

What's the emissivity of the pipe and the aluminum?

What's the pipe? Does it keep it at temp, regardless of how much heat is pulled out?

TTFN

FAQ731-376

 

[Unotec]

Insulate it. If you have to ask these type of questions either the information of your system is incomplete / unavailable to you or you do not quite understand heat transfer. In a case like this, insulate it where the aluminium is. I am not sure why you do not want to heat it up or what the upper limit temperature for it would be. But if you are responsible for some neagtive effects this might have, be practical and insulate it.

 

[jasno999]

I understand there is nto a lot of inforamtion. I don't have all of the information at this time.

Air enviromnet is 120F and there will be some airflow on the outside of the pipe. Don't have a mass for everyhitng- changes depending on location. Basically I have a pipe that will run thru some aluminim.

Pipe stays at temperature. Emissivity could be assumed at 0.9.

 

[pmover]

jasno999

fyi, for personnel protection, surface temperatures exceeding 130 degF are generally insulation to avoid burns to humans. while your situation is not known, it appears the most logical solution is to insulate the pipe.

also, fyi, OHSA (if in USA) has regulations regarding hot surfaces and personnel protection.

lastly, if you insulate, perhaps this website will be of assistance to you.

http://www.insulation.org/techs/3EPlus.cfm

Good Luck!
-pmover

 

[Unotec]

jasno999

I apologize for the way I replied to you. It was quite rude. In my defense, I had just finished up a round with my EH&S advisors and ... well ... I've now got to spend quite a bunch more in my project due to so called safety.

As pmover said, if it is within reach, insulate it. If the aluminium is within reach, still insulate the piping. Wouldn't you want to preserve the heat anyway? Or at least look into scavenging it?