[Tobi]

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

buoyantBoussinesqSimpleFoam

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

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:

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

[Bernhard]

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]

Dear Tobi,

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

regards,

[kakkapriyesh]

Originally Posted by Tobi

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

buoyantBoussinesqSimpleFoam

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

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:

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

were you able to get the turbulent prandtl number for water? I want to run a LES case (wall resolved) and i am concerned that if prt is assumed and not calculated in openFoam then my heat transfer coefficient would be wrong!! according to DNS in viscous sublayer prt for wall jets is more than 1 which goes to 0.85 in log law.(for air)

Thank you
Priyesh Kakka

[calf.Z]

So how can I get the Prt for water and CO2?