# convection heat transfer coefficient

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 February 6, 2014, 15:29 convection heat transfer coefficient #1 New Member   ehsan izadpanah Join Date: Dec 2013 Posts: 4 Rep Power: 4 Hihow 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 butit seems CFX cannot predict bulk temperature.

 February 6, 2014, 17:53 #2 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 12,411 Rep Power: 97 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.

 February 6, 2014, 18:23 #3 Senior Member   Edmund Singer P.E. Join Date: Aug 2010 Location: Minneapolis, MN Posts: 512 Rep Power: 11 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.

 February 7, 2014, 02:51 #4 New Member   ehsan izadpanah Join Date: Dec 2013 Posts: 4 Rep Power: 4 Thanks for your reply Please explain more

 February 7, 2014, 03:03 #5 New Member   ehsan izadpanah Join Date: Dec 2013 Posts: 4 Rep Power: 4 h=q''/(Twall-Tbulk), Tbulk will vary along the channel length

 February 7, 2014, 04:53 #6 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 12,411 Rep Power: 97 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.

 February 7, 2014, 05:36 #7 New Member   ehsan izadpanah Join Date: Dec 2013 Posts: 4 Rep Power: 4 How can I do that in CFX?best

 February 7, 2014, 06:06 #8 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 12,411 Rep Power: 97 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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