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Reference temperature for HTC (internal flow)

    • lilly santana
      Subscriber
      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 that for internal flow problems, the reference temperature is the mass weighted average (see attached image), but how can I calculate this integral?
       
       
       
      Thank you
    • Rob
      Ansys Employee

      Have a look in the volume reports, but "mass flow average" implies a surface report.  The best option is to read the User's Guide chapter which covers the HTC definitions as Fluent has 3-4, the one you want depending on what you're doing. There's a reason we generally report a heat flux! 

    • lilly santana
      Subscriber

      Hi Rob,

      Thank you for your response. Can you send me a link to the guide you're referring to cause I could only find ones detailing the HTC calculation from surface integrals? I inputted the heat flux in the wall BC 'thermal' tab & the reference temp in reference values myself, which I believe are both used to calculate the HTC?

    • Rob
      Ansys Employee

      https://ansyshelp.ansys.com/account/secured?returnurl=/Views/Secured/corp/v222/en/flu_ug/flu_ug_fvdefs.html   You need to access Help via the solve and then paste the link into the same browser. 

    • lilly santana
      Subscriber

      Thanks very much :) so to get the mass-flow average temperature, I've used these settings (the 'Surface' selected is the entire fluid region), but it's saying the static temperature is 0 K & I'm not sure why?

    • lilly santana
      Subscriber

      Sorry, I've had to cross the names out as per my mentor's request *sigh*

    • Rob
      Ansys Employee

      Don't report on the fluid surface, that's what the Volume reports are for. Zero Kelvin shouldn't be able to happen as the solver is limited to 1K. What happens if you plot temperature contours? 

    • lilly santana
      Subscriber

      So which surface should I report it on instead? I'm trying to get the mass flow average temp of the fluid. When I plot temperature contours, the fluid temp appears to be constant and the same as the initial temp I patched it to. I'm not sure why, since I have multiple battery cells which generate around 7W (or 700 W/m^2) of heat to the fluid.

      Thanks in advance!

    • Rob
      Ansys Employee

       

      If the temperature field is constant then generally you’re adding heat into the wrong place, the cell zones aren’t connected or the boundary conditions mean that the heat escapes very quickly. 

      Surface reports are for planes or “surface” entities, eg walls, inlet, outlet etc.  The volume condition is reported for the fluid & solid zones.  In 2d the two should return the same values for the fluid & solid regions. 

      Please post some images of the results so I can see what's going on. 

       

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