Heat transfer in pipes

[nalasimbha]

Hi,

I have a question in calculating Nusselt and friction factor for flow in pipes. The flow in a pipe could be hydrodynamically developing, hydrodynamically fully developed, thermally developing and simultaneously developing and these four scenarios can occur for laminar and turbulent flow conditions.

After evaluating x* (thermal entrance length) and x+ (axial entrance length) for a given pipe of length L and dia D, I would need to select a suitable correlation and evaluate Nu and f. What I would like to know is that, if the length of the pipe is greater than x* and lets say the fluid has a high Pr, then will I use the correlations for fully developed for the entire length or should i used developing flow correlation till the point the flow is developing and then use the fully developed flow equations for the remaining length?

Thank you

 

[ione]

The Nusselt varies (decreases) from the entrance region to fully developed conditions, and Nusselt number behavior is influenced by the thermal and velocity boundary layer (please take a look to the attached paper).

According to what above I would distinguish between entrance region (developing) and fully developed region, and use specific correlations for each region.

 

[ione]

Nalashimba,

Please take a look at the attached paper. You should find useful information on how to handle entry region effect both in the case of laminar and turbulent flow.
I’ve found this paper very interesting, hope it could help you. Let us know.

 

[nalasimbha]

Thank you, ione. Let I shall read through the attachment and get back to you in case I have further questions.

 

[skuntz]

ione:

What is the citation for the latter paper?

 

[ione]

My apologies for having omitted the reference.
I have downloaded this stuff from Notre Dame University web site and saved it as a pdf file as I prefer to handle it this way. Originally it was arranged as a ppt file and these slides are from an intermediate heat transfer course.

http://www.nd.edu/~msen/Teaching/IntHT/Slides/08B - Chapter 8, Sec 8.4 - 8.8 Black.ppt

For further details you can take a glance at the link below

http://www.nd.edu/