# nusselt number calculation

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 October 26, 2011, 17:35 nusselt number calculation #1 Member   Peter Join Date: Oct 2011 Posts: 52 Rep Power: 7 I'm stuck calculating nusselt number and I don't know what I'm doing wrong. I have a fully developed flow passing between infinite parallel plates. The flow is then heated by constant temperature plates. I have calculated a nondimensional temperature field theta. Theta = (T-T_w)/(T_in-T_w) where T_w is the wall temperature and T_in is the inlet temp. To find nusselt number I am using the equation Nu=(dtheta/dy)/theta_avg dtheta/dy is (theta(boundary)-theta(interior))/dy thetavg = theta u* dy this is giving me all sorts of strange results even for the graetz problem. any ideas

 October 27, 2011, 03:42 #2 New Member   Fabian Join Date: Jan 2010 Posts: 27 Rep Power: 8 Where have you found this equation?

 October 27, 2011, 09:15 #3 Member   Peter Join Date: Oct 2011 Posts: 52 Rep Power: 7 I used to equation provided in this paper whose results I am trying to reproduce. The equation for nusselt number is equation 21. http://enstrophy.mae.ufl.edu/~mohsen...008DHTcfd1.pdf

 October 28, 2011, 09:16 #4 Senior Member   Andrew Join Date: Mar 2009 Location: Washington, DC Posts: 195 Rep Power: 9 have you tried different values for dy to see how that affects your answer? You might have to use a small value

 October 28, 2011, 12:00 #5 New Member   Robin Bornoff Join Date: Mar 2009 Posts: 23 Rep Power: 9 How are you calculating T?

October 28, 2011, 12:57
#6
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Peter
Join Date: Oct 2011
Posts: 52
Rep Power: 7
Quote:
 Originally Posted by mettler have you tried different values for dy to see how that affects your answer? You might have to use a small value
I have tried smaller dy and it hasn't really changed my results

Quote:
 Originally Posted by RobinB How are you calculating T?
I'm not really calculating T, but I'm calculating theta on a staggered grid and trying to keep everything non dimensional.

Here is a code I have been using in matlab to test a basic hagen poiseuille flow between two plates and a slug flow between two plates. The Nu number plots show some of the correct behaviors but asymptote to the wrong values.
Attached Files
 verification code.zip (1.9 KB, 10 views)

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