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Nusselt Number calculation in Ansys CFX

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Old   April 24, 2013, 18:18
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Marco Correa
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Quote:
Originally Posted by siavash_y View Post
I have the same problem, did u find a solution marcoac?
Well, not a good one. I found workarounds, not real solutions.

As many users suggested, you can use design modeler to imprint planes along the channel and interpolate them. If you're working with parameters this is the best solution in my opinion because you can write an expression to give you the result right away. It will give you a fairly good idea of what's happening, but may not be as accurate as required.

Another solution is to export temperature and velocity as a csv file and use it in Mathematica (or similar) to interpolate over the domain and extract the results you need.

Regards,
Marco
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Old   February 24, 2015, 12:35
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VIPIN KAKKAR
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Hi,
i am simulating natural convection heat transfer from perforated fin array and have solved the problem in CFX,but i am unable to find out Nusselt number of the fin array.
please tell me how to find out Nusselt number of fin array.
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Old   February 24, 2015, 12:49
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i am working on natural convection heat transfer of perforated fin array in CFX. i have solved it in CFX, now i need to find out Nusselt no. of fin array for that first of all i have to find out heat flux value of fin. The problem is with the post processing software as I don't really know it well enough. How do I extract the heat flux values for my FIN wall?
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Old   February 25, 2015, 11:23
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Edmund Singer P.E.
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Use variable "Wall Heat Flux". This of course assumes you didnt model the wall as adiabatic......
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Old   February 27, 2015, 22:42
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Use variable "Wall Heat Flux". This of course assumes you didnt model the wall as adiabatic......
sir,
may you explain me how to use "wall heat flux" variable. when i select wall heat flux in variable tab it shows value of min & max heat flux, whether this min & max value is for whole body?
i want to find out Average heat flux for a single body & single surface. Please tell me how to find out.
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Old   February 28, 2015, 07:29
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Glenn Horrocks
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The min and max refer to the object locator it is referring to.

Use the function calculator to calculate any function of any area.
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Old   March 1, 2015, 09:17
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The min and max refer to the object locator it is referring to.

Use the function calculator to calculate any function of any area.
sir,
i am finding heat flux using two expressions- areaAve(wall heat flux)@location and ave(wall heat flux)@location.
value for both the expressions is different.
what does function areaAve and ave mean?
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Old   March 1, 2015, 18:18
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This is explained int he documentation, in the CFX reference guide. areaAve is the area weighted average and ave is just a simple arithmetic average.
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Old   March 2, 2015, 00:41
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This is explained int he documentation, in the CFX reference guide. areaAve is the area weighted average and ave is just a simple arithmetic average.
Thank you sir for your suggestion!
sir,please tell me one more thing what does areaAve(Temperature)@location
" area weighted average temperature" mean. Is it absolute temperature or relative temperature(difference of absolute and atmospheric temperature).
In my fin array problem when i gave heat flux 5900 W/m2 to fin base then areaAve(Temperature)fin shows 140 K.
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Old   March 2, 2015, 00:57
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The temperature returned will be the temperature variable - that will be defined as C, F or K depending on your setup. And it is an absolute value, not a relative one.

If you have and areaAve(temperature) of 140K then your fin is really cold. This is 140K absolute, so 133K below the freezing point of water. I hope this is what you intended to do.
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Old   March 3, 2015, 07:43
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Originally Posted by ghorrocks View Post
The temperature returned will be the temperature variable - that will be defined as C, F or K depending on your setup. And it is an absolute value, not a relative one.

If you have and areaAve(temperature) of 140K then your fin is really cold. This is 140K absolute, so 133K below the freezing point of water. I hope this is what you intended to do.
Thank you sir!
sir, in my problem of "natural convection heat transfer from perforated fin array", i can calculate heat flux and temperature at any face of fin array in CFX-post ,but how to calculate Nusselt Number of Fin Array in CFX-post
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Old   April 2, 2015, 09:58
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sir please tell me how to find wall heat transfer coefficient and wall adjacent temperature. what are expressions to find these variables.
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Old   April 2, 2015, 10:24
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I don't understand your question...
you have the name of the variable so you can plot it in CFD-Post...
both of them are Wall variable so plot it on the Wall with a contour.
For better understanding use the CFD-Post Help on these variable and the CEL function...
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