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Heat transfer coefficient for laminar internal flow

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Old   September 28, 2022, 19:45
Default Heat transfer coefficient for laminar internal flow
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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?

https://www.youtube.com/watch?v=PuTl98d0iZ0&t=1264s

Thank you
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Old   September 29, 2022, 00:12
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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.
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Old   September 29, 2022, 06:54
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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?
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Old   September 29, 2022, 11:44
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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
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Old   September 30, 2022, 13:15
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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?
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Old   September 30, 2022, 13:20
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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.
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Old   October 3, 2022, 08:14
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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
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