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HEELP !! safety Tubes ( double wall)

HEELP !! safety Tubes ( double wall)

HEELP !! safety Tubes ( double wall)

(OP)
Hi there !!

How can I calculate with HTRI an exchanger with double wall tubes. It's practically a safety exchanger with a OD 19.05mm ( ID 14.5 mm) 19 FPI copper tube on the outside and 1 OD 14mm tube on the inside (ID ~12 mm)?

Hoe can I simulate such a tube ? (Let's say that:
in the intermediate chamber there is compress air)

Thank You in ADVANCE

 

RE: HEELP !! safety Tubes ( double wall)

Is there any conductive material in the .25mm spacing between the tubes?

RE: HEELP !! safety Tubes ( double wall)

With such a narrow gap, that air can be treated as a purely conductive medium.  There would be no convective whatsoever in the gap.

TTFN

FAQ731-376: Eng-Tips.com Forum Policies

RE: HEELP !! safety Tubes ( double wall)

(OP)
THank you for the help !!

By considering the air a pure conductive medium, I should consider it like a tube with a thickness of 19.05-12 =3.5 mm with a resistance due to the sum of (2.5/K(copper) + 0.25/K(air) +1/Kcopper)  or more simply 0.25/K(air).

 

RE: HEELP !! safety Tubes ( double wall)

(OP)
Right question !!

Since the pressure will be at around 15 bar.
Since the conductivity is very low, this could be a relevant step in the right direction !!

Thank you very much for the tip !!

Do you know where I could find a table with these values ?

Thank you very much !!

 

RE: HEELP !! safety Tubes ( double wall)

(OP)
Oops i forgot,
 the temperatura will be around 40°C
 

RE: HEELP !! safety Tubes ( double wall)

(OP)
By the way I have another issue !!

THe tube is finned with 19 FPI geometry. the conductivity value that i'm going to insert will not "interfere" with the parameters of the finns ( which are in copper). I mean it has sense simulate the air just changing the conductivity values , or it's a too rude approach ?

Thank you in advance !!

RE: HEELP !! safety Tubes ( double wall)

??? are the fins in the gap?  if so, then they're in parallel, but you can treat them like parallel thermal resistances, so the net thermal resistance would be lower, if that's the case.

I don't do much with gas properties, but NIST has a database somewhere with that information:
http://www.nist.gov/srd/WebGuide/nist72/72.htm
http://srdata.nist.gov/gateway/gateway?property=standard+air

Engineering Toolbox might have something:
http://www.engineeringtoolbox.com/air-properties-d_156.html

TTFN

FAQ731-376: Eng-Tips.com Forum Policies

RE: HEELP !! safety Tubes ( double wall)

(OP)
Actually the tube is finned on both side internally and externally .

THe question is how it will behave externally with the new fins?

Thank you very muche for the tip for the series !!

  

RE: HEELP !! safety Tubes ( double wall)

for SHORT fins, they simply add to the surface area

for fins between the two tubes, you would simply determine the thermal conductivity of the fins and add to that the thermal conductivity of the air between the fins.  If there are a lot of fins between the tubes, you might be able to ignore the air altogether.

TTFN

FAQ731-376: Eng-Tips.com Forum Policies

RE: HEELP !! safety Tubes ( double wall)

(OP)
Thank you very much for the help and the precious tips !!


 

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