heat transfer coefficient - forced convection
Dear Gurus, please help me to solve the following problem:
TARGET: to map the convective heat transfer coefficient (H.T.C., h_cell, [W/m2 K]), without using the energy equation (the "cold" approximation I mean) using a cell by cell formulation, along the frontier of a 3D very complex geometry (many characteristic lengths, confined domain, forced convection)
Velocity and pressure field are known everywhere (already computed with a RANS FVM code). Lots of velocity gradients are present inside the whole domain. The flow is incompressible with M << 0.3 and isothermal, Pr = 0.7.
Someone told me to use the flat plate approximation computing for each wall cell the local Nusselt relation like this:
Nu(x) = c * (Re(x)^n )* Pr^m
where c, n and m are the laminar/turbulent coefficient suggested by Schlichting ("B.L. Theory" pag. 298-299)
Re(x) = density * vel_cell * x / viscosity
and substituting in:
h(x) = k * Nu(x) / x
to obtain the H.T.C., h(x).
The main problem is:
> what is "x" for my 3D CFD problem cell by cell based?
> Is a correct approximation to choose the wall cell mean length as "x" supposing that this dimension is inside the boundary layer (x=Lmean_cell)?
> What is the best choose for vel_cell?
Any contribution would be really appreciated.
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