# Heat transfer coefficient for laminar internal flow

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September 28, 2022, 19:45
Heat transfer coefficient for laminar internal flow
#1
New Member

Avon
Join Date: Aug 2022
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Hi,

I have a 2D, steady state, laminar internal flow problem. I think the calculation for laminar flow HTC is: HTC = q / (T_wall - T_ref); where T_ref is the reference temperature. What I'm stuck on is how to define this reference temperature for my problem. This video says it's the mass weighted average (see attached image), but how can I calculate this integral?

Thank you
Attached Images
 internalflow.jpg (58.7 KB, 16 views)

 September 29, 2022, 00:12 #2 Senior Member   Lucky Join Date: Apr 2011 Location: Orlando, FL USA Posts: 5,062 Rep Power: 60 To calculate the mass flow weighted average at a particular location, create a surface average report/monitor and choose mass average and select temperature as the variable of integration.

September 29, 2022, 06:54
mass average
#3
New Member

Avon
Join Date: Aug 2022
Posts: 23
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Thank you very much for your response. So do I first run the calculation and then select the options in the image I've attached? if I do so, idk what I should input for the reference temp in the 'reference values' section during this initial run, since T_ref is what I'm trying to find.

I'm also unsure how this is at a particular location?
Attached Images
 mass_ave.jpg (84.1 KB, 11 views)

 September 29, 2022, 11:44 #4 Senior Member   Lucky Join Date: Apr 2011 Location: Orlando, FL USA Posts: 5,062 Rep Power: 60 It is at a particular location because you choose an input surface, an area, over which to do the integral. That is, you must select one of the red thingies you have censored out. If you need the reference temperature at a different location that is not one of the surfaces on this list, then you create it, and then click it. The reference values panes affects only post-processing does not affect the solution. Just press the calculate button

 September 30, 2022, 13:15 #5 New Member   Avon Join Date: Aug 2022 Posts: 23 Rep Power: 2 My mistake sorry, just realised what you meant! I selected the entire fluid region for 'Surfaces'. So can I first run the simulation with the T_ref value = inlet temperature, then when the calculation is complete, use the options in the Surface Integrals dialog to print the actual T_ref in the console, and then re-run the simulation with the new T_ref, which will be used to get the HTC?

 September 30, 2022, 13:20 #6 Senior Member   Lucky Join Date: Apr 2011 Location: Orlando, FL USA Posts: 5,062 Rep Power: 60 You can update the reference temperature at any time and then replot without rerunning. HTCs are post processed quantities. The temperature solution and heat flux are the same regardless of your input for the reference temperature. You don't need to rerun/reiterate just to get the same temperature and heat flux again. CFD10111 likes this.

 October 3, 2022, 08:14 #7 New Member   Avon Join Date: Aug 2022 Posts: 23 Rep Power: 2 I see. I inputted the heat flux value in the thermal tab for the battery cell wall BCs. I changed the reference temp value after the initial run (without rerunning) despite it still saying 'compute from inlet' - hope this is ok since my new T_ref is the mass flow average temp & not the inlet temp