CFD Online Discussion Forums - transportProperties

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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?

Thanks in advance
Tobi

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,

$-\overline{\theta'u'_j}=\alpha_t\frac{\partial\overline{T}}{\partial x_j}$
and then it is assumed that $\alpha_t$ scales wit $\nu_t$ or $\alpha_t=\frac{\nu_t}{Pr_t}$ , 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.

multiRegionLiquidHeater

Dear Tobi,

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

regards,