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 Tobi December 4, 2012 20:24

transportProperties

Hi all,

i want to simulate an liquid cooler for a CPU. For that I had a look into the solvers and thought that the solver
Code:

 buoyantBoussinesqSimpleFoam
for turbulent incompressible fluids are good.
For that I have to change the transportProperties file from air into water (25°C)

Code:

transportModel Newtonian; // Laminar viscosity nu              nu [0 2 -1 0 0 0 0] 0.89e-06;      // Thermal expansion coefficient beta            beta [0 0 0 -1 0 0 0] 0.0018; // Reference temperature TRef            TRef [0 0 0 1 0 0 0] 298; // Laminar Prandtl number Pr              Pr [0 0 0 0 0 0 0] 6.1; // Turbulent Prandtl number Prt            Prt [0 0 0 0 0 0 0] 0.38;
Are this settings correct? How can I estimate the turbulent prandtl number in that problem?
In my case I calculated the turbulent prandtl with that equation:

Code:

Prt = 0.7 * a / nu_t
With the turbulence calculator on that website I calculated k and omega from U, I and length scale.
After that I calculated mu/mu_t and then nu_t = mu_t/rho.

Is that correct?

Tobi

 Bernhard December 5, 2012 04:55

The turbulent Prandtl number is not really a property of the liquid. You obtain it from the Boussinesq (or gradient diffusion) hypothesis (not to be confused with the Boussinesq approximation) from the turbulent heat flux,

and then it is assumed that scales wit or , but this is by no means a way to estimate the turbulent Prandtl number. It is a property of the turbulence more than a property of the liquid. I think in general, is somewhere in the range 0.7 to 0.9. But please read a bit more on this in books or papers to be absolutely sure.

 Ahmed Khattab December 30, 2012 04:30

multiRegionLiquidHeater

Dear Tobi,

a good start could be from a neighbor case multiRegionLiquidHeater .it contains a file for water properties.

regards,

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