Nusselt number calculation

dreamz · April 13, 2014, 06:16

I want to plot nusselt number along the length of a heat generating plate. The plate is cooled by natural convection currents around it. I have created a line on the plate.

I am referring the following tutorialhttps://confluence.cornell.edu/display/SIMULATION/2D+Steady+Convection+-+Numerical+Results

They have taken a temperature at wall Tw. Then they evaluate bulk mean temperature. However, my wall temperature varies with length as my plate is cooled by natural convection? How then should I proceed?

som87 · April 14, 2014, 04:22

So, whats the problem with calculation of bulk mean temp with varying Tw along the plate...? Sorry I could not follow

dreamz · April 14, 2014, 11:44

In the tutorial they have put an expression for Nusselt number, which gives Nu at a point. Now, what I want is variation of Nusselt number along a line. So, first I should have Tw which varies along the wall. Also, the heat flux is also varying along the wall. How to incorporate that in the Nusselt number expression? Second thing, how then to find nusselt number expression at all points and get a variation?

Essentially, I think I will have to find Tw, q and thereby Nu at different points. Then export them to excel and plot a graph. Is their a direct way to do it in CFD post just the way we get temperature distribution along a line?

DaveyBaby · April 14, 2014, 16:02

This really is a question for Ansys users as opposed to general CFD. In Star CCM+, you CAN use the outputs from user-defined expressions as the input for another user-defined expression, which is calculated on the same time-step/iteration as it's inputs. I would be surprised if Fluent can't do this, you would need to check their help section for how to reference user defined expressions within another user-defined expression.

April 13, 2014, 06:16	Nusselt number calculation	#1
dreamz Member Ashutosh Join Date: Jul 2013 Posts: 98 Rep Power: 13	I want to plot nusselt number along the length of a heat generating plate. The plate is cooled by natural convection currents around it. I have created a line on the plate. I am referring the following tutorialhttps://confluence.cornell.edu/display/SIMULATION/2D+Steady+Convection+-+Numerical+Results They have taken a temperature at wall Tw. Then they evaluate bulk mean temperature. However, my wall temperature varies with length as my plate is cooled by natural convection? How then should I proceed?

April 14, 2014, 04:22		#2
som87 Member Join Date: May 2012 Posts: 68 Rep Power: 14	So, whats the problem with calculation of bulk mean temp with varying Tw along the plate...? Sorry I could not follow __________________ Best wishes, Somdeb Bandopadhyay

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April 14, 2014, 11:44		#3
dreamz Member Ashutosh Join Date: Jul 2013 Posts: 98 Rep Power: 13	In the tutorial they have put an expression for Nusselt number, which gives Nu at a point. Now, what I want is variation of Nusselt number along a line. So, first I should have Tw which varies along the wall. Also, the heat flux is also varying along the wall. How to incorporate that in the Nusselt number expression? Second thing, how then to find nusselt number expression at all points and get a variation? Essentially, I think I will have to find Tw, q and thereby Nu at different points. Then export them to excel and plot a graph. Is their a direct way to do it in CFD post just the way we get temperature distribution along a line?

April 14, 2014, 16:02		#4
DaveyBaby Member DaveyBaby Join Date: May 2013 Posts: 46 Rep Power: 13	This really is a question for Ansys users as opposed to general CFD. In Star CCM+, you CAN use the outputs from user-defined expressions as the input for another user-defined expression, which is calculated on the same time-step/iteration as it's inputs. I would be surprised if Fluent can't do this, you would need to check their help section for how to reference user defined expressions within another user-defined expression.