×
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

Heat transfer in duct with different cross section

Heat transfer in duct with different cross section

Heat transfer in duct with different cross section

(OP)
Hello

what is the difference in free convection in a duct with circular cross section and rectangular cross section. is this correct that temperature difference  decreases exponentially with distance along the duct (circular cross section )but linearly in ractangular duct?
thx

RE: Heat transfer in duct with different cross section

I think that in many cases the rectangular duct can be considered circular by using the hydraulic diameter of the duct.  Get a hold of a textbook on heat transfer, and you should find an explanation of the hydraulic diameter and its use in equating a rectangular duct to a circular duct.

In regard to exponential versus linear variations with temperature difference, I don't think it has anything to do with the duct cross section.  The type of variation in temperature difference along the duct is dependent on the boundary conditions at the external surface of the duct.  Two examples are constant temperature or constant heat flux at the duct's outer surface.  I forget which is which, but a decent heat transfer book should contain details on the differences.

It's not the complete answer, but I hope it helps you get started.

RE: Heat transfer in duct with different cross section

First of all, what type of accuracy is needed?
What is the orientation of the duct?  vertical, horizontal or what ever?
Hydraulic radius will not necessarily give accurate results.  ----unless one has experimental data in terms of dimensionless numbers using the hydraulic radius.

RE: Heat transfer in duct with different cross section

(OP)
Thank you for your comments the duct is horizental and i want to know for 2 ducts with same cross section area but with diffrent cross section shape what is the heat transfer behavior in this case ?
thx
 

RE: Heat transfer in duct with different cross section

Sorry, but some other information is needed.
Since you state natural convection, I assume there is no net horizontal flow.
For a horizontal circular duct, with for example, a uniform temp on its inside surface, I would expect circulation, but with the bulk inside fluid at the temp of the inside surface.
For the rectangular duct, are the boundary conditions of duct temp the same? If so, the same result as for the circular duct.
Please give more information as to the boundary conditions and if there is to be a net horizontal flow.
Otherwise, the problem is not making too much sence with me.

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