heat transfer in finned tube

[morojlu]

Hi
I read in some standard that minimum contact pressure to joint of fin to tube is 25 kpsi. if the contact pressure is less than this (for example 5 kpsi) how much heat absorbtion will be deacreasd in finned tube? (assume that there is not mechanical problem like existing of gap between fin and tube)
thanks

 

[thermcool]

I think the 25 Kpsi is only the recommended pressure for applying the fins to the tube. what sort of heat transfer issues that can come at low pressure is very improbable. You might get a same heat transfer as 25 kpsi fin attachment, particular as you are saying if you are assuming there is no mechanical gap. The best way is to do a simple experiment and measure the temperature on the fin base and fin tip. Try to calculate the heat transfer from this information by using fin analogy. You can also calculate the heat transfer theoretically on the basis of the heat transfer from the extended surface (fin approach) and see how much the heat transfer is affected by decreasing the attachment pressure.

Attachement pressure plays a vital role in the heat transfer and thermal resistance at the interface but it is very improbable parameter to guess or predict. The best way is expermentation.

 

[davefitz]

My guess is that the required contact pressure is assocaited with the fin material yield stress, which varies for each different material and alloy.

There are likely to be lab tests for the most likelyused alloys of contact heat transfer resistance vs contact stress .