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Old   February 6, 2014, 15:29
Default convection heat transfer coefficient
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ehsan izadpanah
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Hi
how can I obtain convection heat transfer coefficient in channel for constant temperature wall BC using CFX. To calculate h in internal flow we need to have bulk temperature at even cross section but
it seems CFX cannot predict bulk temperature.
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Old   February 6, 2014, 17:53
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Glenn Horrocks
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There is an expert parameter so the h is referenced to a bulk temperature you define. Search the forum to find it.

Alternately you can use the wall heat flux variable available in the post processor and your own reference temperature and work it out. You could define it as a variable and have it available for post processing.
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Old   February 6, 2014, 18:23
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Edmund Singer P.E.
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Glenn's second suggestion is often much more useful. The problem with the expert parameter is that the bulk temperature has to be constant (not an expression as to pull a different bulk from different locations). Using his latter suggest allows bulk temperature to be pulled from CFX in a manner consistent with text books.
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Old   February 7, 2014, 02:51
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ehsan izadpanah
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Thanks for your reply
Please explain more
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Old   February 7, 2014, 03:03
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h=q''/(Twall-Tbulk),

Tbulk will vary along the channel length
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Old   February 7, 2014, 04:53
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You can define Tbulk to be anything you like, and it does not need to constant. If you want it to vary along the channel length then make Tbulk a function of position and calculate h from that.
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Old   February 7, 2014, 05:36
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How can I do that in CFX?
best
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Old   February 7, 2014, 06:06
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Define a new variable in CFD-Post, defined as CEL expression Wall Heat Transfer/(T-Tbulk). Then you can define Tbulk as a constant (eg 280[K]), or as a function of distance (Tbulk = 300[K] + 10[K/m]*x).

If you do not know how to do CFD-Post variables have a look in the CFX tutorials.
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