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Units for expert parameter "tbulk for htc"

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Old   October 30, 2005, 08:09
Default Units for expert parameter "tbulk for htc"
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Hi everyone,

A simple question: I am about to change the 'tbulk' value in my *.def files in order to account for the fluid 'bulk' (unperturbed) temperature in the calculation of the heat transfer coefficient. All the settings accounts for Celsius centigrade scale, but in the Help section (CFX user guide) says that 'tbulk' (in expert parameter menu) is given in 'Kelvin' scale. So, the question is, if the unperturbed fluid temperature is 20 C then the value for 'tbulk' is


tbulk= 293.15 K???.... does 'tbulk' MUST be in Kelvin??

I need to set this in order to correctly compare the results against experimental data.

......In another 'message' I read that when this value is NOT specified, then the software 'assumes' a 'tbulk' temperature corresponding to the temperaute value of the 2nd cell of the model (???). Another 'message' says that 'tbulk' is taken as Tnw, and this Tnw is given by the wall function... then this would imply that I would have 'htc' given on a non-uniform 'tbulk' data, since Tnw varies around the model wall.... so in order to avoid this confusions I want to give an specific value, so I can use 'safely' the 'htc' values for comparisons and 'FEM' structural analyses.

If Tnw is given near the end of the thermal boundary layer (turbulent case), can I assume that Tnw--> 'Tinfinity'??

PS. My model is a rotating heated channeled disc in turbulent fluid.

I appreciate your comments.

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