How to Correlate The Average Nusselt Number

Replies

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  samko95

  Which site can help please ?
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  Ramani Aswath

  Is this about any specific problem or in general?
  This one?
  #-Link-Snipped-#
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  samko95

  Thank you for your reply
  I've simulated finned tube heat exchanger with circular fin (sold fin and perforated fin with different perforation shapes).
  I've got all results (HTC,pressure drop at different velocities), but I've no idea about my previous question.
  Your link may be useful, but the button of tube bank does not work(404 Not Found).
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  Ramani Aswath

  That is interesting. Do perforations really increase HTC substantially? What happens to the pd at different velocities. I would have thought that if the area of perforation is a significant portion of the fin area HTC may come down for same gas flow velocities. It may be argued that the possible extra turbulence created by the perforation will improve HTC. The downside is the pd.
  In any case, some of these non standard geometries cannot really fit into the traditional equations. Unless this is an academic programme, good empirical data is of more value than some approximation of existing formulae.
  You can even come up with a Samko number!
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  samko95

  A.V.Ramani

  That is interesting. Do perforations really increase HTC substantially? What happens to the pd at different velocities. I would have thought that if the area of perforation is a significant portion of the fin area HTC may come down for same gas flow velocities. It may be argued that the possible extra turbulence created by the perforation will improve HTC. The downside is the pd.
  In any case, some of these non standard geometries cannot really fit into the traditional equations. Unless this is an academic programme, good empirical data is of more value than some approximation of existing formulae.
  You can even come up with a Samko number!

  In my results I found some investigation. I had expected that HTC investigation my be small due to constant pressure on the tow sides of fin, but my supervisor constrain me. depending on several articles I was choose suitable perforation position. Naturally PD will be increase with perforation but I'll got more heat transfer and this is more important to me than PD.
  What is the solution Mr.? do you have any idea?.
• 

  Ramani Aswath

  The gas side HTC is very much lower than the liquid side HTC, which is why fins are used. However, if the fins are perforated then the perforated area is lost to heat transfer. Since you are not bothered by PD issues, you can consider piercing the fins with a conical tool to get a hole with an extended projecting skin somewhat like this:
  
  
  The jagged edge of the hole as in the sheet metal sample above will be in the gas flow stream and create turbulence which will help HTC. Because of the punch-extrude process the area will actually increase.
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  samko95

  I agree with you, in addition to increase in area the turbulent must be increase due to large destruction in boundary layer by this conical perforation(I can't see the pic.). Also in my case the air will not through the perforation, while its a certain thing in your case. All my results were completed and I can't change anything now, I've to solve my problem now.
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  Ramani Aswath

  Have you seen published data on Nusselt number related to finned tube exchangers?
  Pleas check if any of these is useful:
  #-Link-Snipped-#
  Nusselt Number
  #-Link-Snipped-#
  PDF
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  samko95

  I am checked this data already, It is just give the final form without talk about the used way.
  Thank you for your attention
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  darshil shah

  i have some specific fin geometry. i request you send your mail id. so that i can send you the pics of fin geometry.
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  darshil shah

  
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  samko95

  I did not understand what are you talking about, can you explain more please?