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 Diana.N February 9, 2012 01:32

Problem in post processing

Hiall, I'm new to this forum and joined since I have a CFD problem
I need to post process results of Fluent for Nu number and friction factor for concentric pipe under constant heat flux insertedwith twisted tape.

Regards

 delaneyluke February 10, 2012 02:31

You will have to create custom-field functions for these parameters as they are not directly available as default variables.

Regards
Luke

 Diana.N February 10, 2012 05:05

Problem in Post processing

Hello Luke,

Thank for your Advice, but my problem is how to select surface to
post process the result and how to calculate the Nu number for the
pipe especially with inserts.

I kindly ask you to Guide me to calculate Nu number.

Regards
Diana

 delaneyluke February 10, 2012 05:14

http://www.wlv.com/products/databook...ata/db3ch5.pdf
Check out this document, Sub chapter 5.4 talks about pipes with twistred pipe inserts. It gives you the correlation for Nusself number.
With regards to Fluent, if the surface of your interest is already there, you need to select it and plot your variable, or else create an iso-surface and then plot your variable.

 Diana.N February 10, 2012 10:51

Problem in Post processing

Hello Luke,

This document I have already, but my problem regards to Fluent, how
can I select the average value of Nu number can I gate on value on the surface of cylinder or different value and then take the average value.
If I do it on what part of report should I take it can guide you me please.

With Regards

Diana

 ashgun September 24, 2012 14:21

regarding Nu and f

u will have to calculate local Nusselt number at different points along d length
to calculate Nu u will need difference between surface temperature and avg.temperature at given cross section. the cross section u can get from iso-surfaces, go to mesh option then along d direction of length create cross sections. There is an option called rake/line. rake (discrete point) u can choose. It depends on u how many sections u want then create surface using rake point at x or y equal to ur radius of pipe u will get surface temperature.( r should be same no i.r. +r to +r and -r to +r).
and avg. cross section temperature u can get it from mass weighted value of temperature over given section.

then Nu= q/ (Tsurface -Tavg.) q= constant heat flux which is known

for f u can find overall f get delta P over test section and average velocity and use dercy weisbatch equation or f= 8 tau/ rho* v^2

i am also working same topic but mine is partially extended twisted tape i hope its useful

 shk12345 September 25, 2012 11:43

Quote:
 Originally Posted by Diana.N (Post 343504) Hiall, I'm new to this forum and joined since I have a CFD problem I need to post processi.e results of Fluent for Nu number and friction factor for concentric pipe under constant heat flux insertedwith twisted tape. I will much appreciate your advice & comments . Regards
Nu number is already in built in fluent in temperature pannel so you can plot it directly.
Just make a plane anywhere you want and plot the Nu there.
For friction factor f=16/Re, define a custom function and the plot it in the same above fashion.
Hope that will solve your problem.
Need any help . comment.

shk

 ashgun September 25, 2012 13:03

i think 16/Re is theoretical expected value actual value u have to find out by computing pressure drop and velocity

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