×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Free Cooling

Free Cooling

Free Cooling

(OP)
Hi there,

hope all is fine.
Please I would have to calculate an heat exchanger in free cooling.
This means that in this case there is no forced convection but only natural convection with one of the two fluids.
The heat exchange is driven by the temperature difference.

I suppose that epsilon-NTU method can't be used, since Cmin is 0, so NTU is infinite and efficiency is 1.

Please, can anybody of you suggest me how to calculate this type of heat exchanger ?
A practical example would be the simplest solution.

Many thanks

 

RE: Free Cooling

How could Cmin be equal to zero?

RE: Free Cooling

What's the configuration of the heat exchanger?  

Why can't you calculate the natural convection heat transfer coefficient for the fluid in natural convection?  For example, I'm pretty sure I remember seeing how to calculate the natural convective heat transfer coefficient from a horizontal tube bundle in  my university heat transfer textbooks.  I'll have to check tomorrow as that particular book and my Perry's is at the office.

RE: Free Cooling

(OP)
to mr Ione.
Since there is no air flow in front of the coil, I consider Cmin = 0
Please, is it wrong ?

To Mr.TD2K
I would be grateful if you could give me your feedback.

Many thanks

RE: Free Cooling

(OP)
To Mr. Ione.
many thanks

As a matter of fact I am afraid of not understanding.
If I well understand this correlation provides a Nusselt number, that is an heat exchange coefficient.
Now: the problem is that I can even have the internal and external coefficient, the two heat exchange areas - internal and external - the two temperatures, but I am missing the final temperature for the two fluids in order to apply LMTD.
Please, may I ask you an example of how applying this correlation ?

Many thanks

RE: Free Cooling

It's an iterative process, unless you have a solver.  You assume values for the temperatures and iterate until the energy transferred is the same at all interfaces.

TTFN
FAQ731-376: Eng-Tips.com Forum Policies

RE: Free Cooling

Hi

I think that still one equation is missing since there are three unknowns

Unknown:
1 - t cold outlet
2 - t hot outlet
3 - capacity

available equations
1 - Q = m*c*(tin-tout)      (for water)
2 - Q = UA*LMTD

It seems one equation is missing since it can't be utilized the one similar to 1 for air since air mass flow is not known.

What do you think about ?

RE: Free Cooling

(OP)
To Mr IRStuff

please, could you post an example of calculation ?

It would be extremely useful for me.
All in a all I am stuck to the post of Mr. TeeAr

Thanks in advance

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources