Fluids

Fluids

HTC Nu and f

    • jhjang
      Subscriber

      Hello everyone,


         I am trying to simulate 3D laminar developing flow and heat transfer in dimple enhanced pipe. The details are Different cases


      Mesh


      Tetrahedral mesh, 5 inflation layer on the wall


      Model:    Laminar


      Material:   Air


       Boundary conditions:


      Velocity inlet 


      Pressure outlet


      Constant wall heat flux= 50w/m^2


      Reference value: length 0.04m


      Residual: 10^-4 for all except energy 10^-6


       Results


      When I calculate Nusselt number in this way…


      Surface integral Area-weighted average wall fluxes Nusselt number & Skin friction factor, I feel these results are not in the right pattern...



      here the trend of results for both Nu and skin friction is in opposite order.


       Please help me to calculate local and average Nusselt number and friction factor.

    • DrAmine
      Ansys Employee

      Are you using the skin friction coefficient and Nusselt number from Fluent? Here you need to tune the reference values to match your case.

    • DrAmine
      Ansys Employee

      Regarding the results we can only make an evaluation if you clarify the way you obtained the quantities. But the simple Reynolds Analogy tells that the Stanton number is half of the Friction coefficient.

    • jhjang
      Subscriber

      Thank you, sir,


      yes, I am using skin friction factor and Nu number from fluent. Will the reference value change for the enhanced pipe? I use the pipe diameter for both smooth and enhanced pipe as the reference length and inlet area as the reference area during setup.

    • jhjang
      Subscriber

      sir, I am attaching my mesh and case and data file.


      case 2 Re 1000 case and data file


      https://drive.google.com/open?id=15ryhMiw8z8LkBYDsukVIA9l_htz-ynUX


      case 2 mesh file


      https://drive.google.com/open?id=1fymWAOxYAgDbEty7M0rk0nVZe_6uk0rr


       

    • DrAmine
      Ansys Employee

      Yes the reference values are use to calculate the dimensionless number like L_ref, v_ref, roh_ref....Just check the manual.


      I apologize but as ANSYS Stuff I won't look into the cases you are sharing. Be aware that you are sharing files on an open community.

    • jhjang
      Subscriber

      Is there any formula for laminar developing flow to calculate HTC, Nu?


      Because i see some resources using (h=Q"/area*(tw-tm)), where Tw using maximum temperature at the wall and Tm as mass weighted avg. temperature


      "(integration(velocity*temperature*radius)/integration(velocity*radius)) " at axial location z.


      Is this formula for HTC  be applicable to the laminar developing case?

    • DrAmine
      Ansys Employee

      The reference temperature to calculate HTC is always case dependent and might also depend on whehter you have exp. data or other cross-references. I generally use a mass-weighted Average of the temperature at the cross-section at position X where I want to get HTC. Others uses the inflow temperature or volume weighted temperature..

Viewing 7 reply threads
  • You must be logged in to reply to this topic.