# free convection inside tube

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 March 12, 2013, 07:24 free convection inside tube #1 New Member   Join Date: Mar 2013 Posts: 15 Rep Power: 5 Hello!! i am new in CFX and a need your advise in a simulation i am trying to perform. My geometry consists of a vertical conical tube. All i want to do is to set different values for temperature at the top and the bottom boundary in the same time and as a result create recirculation inside tha tube. My working fluid is water. The geometry dimensions are:3 microns diameter at the bottom 1 micron diameter at the top 2.5 mm length. Any advice on the boundary conditions I should use?

 March 12, 2013, 18:17 #3 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 12,707 Rep Power: 98 As stated in the previous thread already quoted, the key non dimensional number is the Rayliegh number. I suspect the Ra number here is quite low meaning the flow is laminar and dominated by conduction. The bounadry conditions you describe sound trivial to set up. Have you done the tutorials?

 March 13, 2013, 04:09 #4 New Member   Join Date: Mar 2013 Posts: 15 Rep Power: 5 I have solved the most of the tutorials. I am quite familiar on the free convection theory but i am still learning. Please give me at first some advice on the kind of boundary conditions you would use in an enclosure similar to this supposedly that the aspect ratio is low and the Rayleigh convection is valid. i think wall at different constant temperatures for the top and bottom plates and adiabatic wall for the rest boundary. the run could be both steady state and transient?

 March 13, 2013, 07:02 #5 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 12,707 Rep Power: 98 The boundary conditions must match what you are modelling. I have no idea what you are modelling so cannot help. If you describe what you are modelling we might be able to help you.

 March 13, 2013, 07:10 #6 Senior Member     Mr CFD Join Date: Jun 2012 Location: Britain Posts: 312 Rep Power: 7 Please provide an annotated diagram. The annotations should state what your boundary conditions are.

 Tags conical tube, free convection

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