[§$§eth]

Hallo @ all,

I am new here and I am new to star ccm+ too.

Also english is not my first language, so sorry for all the faults.

I need help with a strange problem, i want to simulate the cooling down of an tank filled with a liquid set to a specific temperature, for this purpose i have generated a simple geometry a outer cylinder for the solid (concrete)
and a inner cylinder filled with the liquid (water etc.), they are both connected with a interface
the outer boundaries of the outer cylinder are set to enviromental
when i start the simulation the outer solid clyinder behaves like expected but the liquid in the inner cylinder is not cooling down,
i have an heat transfer over the interface between the solid and the liquid regions i checked this and the temperatur of the liquid adjadcent to the solid wall changes,
but the liquid as a whole does not cool down i have waited of hours insimulation and outsimulation but it never changes please help me

i think there has to be somthing wrong with my choosen physics, it is almost like there is an hiden heat source in the liquid

[siara817]

Have you selected Gravity model in Physics?
Check also to ensure that you have not selected constant density for your liquid.

[rwryne]

Originally Posted by siara817

Have you selected Gravity model in Physics?
Check also to ensure that you have not selected constant density for your liquid.

And when you do turn on gravity, make sure its pointing the right direction. I think it defaults to -Z but not sure.

[§$§eth]

Thank you rwryne and siara817 for your answers, the physics for the solid region of the outer cylinder are: three dimensional/ gradients/ solid: concrete/ implicit unsteady/ constant density/ coupled solid energy the physics for the fluid region of the inner cylinder are: implicit unsteady/ three dimensional/ liquid: Al/ laminar/ polynomial density/ coupled energy/ coupled flow/ gravity so yes gravity is activated (in the right direction i checked) and i have not selected constant density for the liquid natural convection is happening in the simulation it almost looks like as if the whole liquid region is set to isenthalpic but how could that be? i would be very grateful for any suggestion thank you

[rajeev50588]

Dont keep the liquid density as constant. There are options of power law, polynomial in T, Sutherland law etc... ( i m not sure if all these options are present for density...pls check). When temperature effects are present in the simulation..usually it is not recommended to keep the density as constant. With change in temperature, density changes...
see if it works

[cwl]

Indeed - if you neglect convection (set Constant Density and/or no Gravity) - your liquid will be cooled down only due to heat conductivity; this will take really much time - taking into consideration its Specific Heat and Heat Conductivity.

[§$§eth]

Originally Posted by §$§eth

....the physics for the fluid region of the inner cylinder are: .... polynomial density/....

thank you for all your help but the liquid is not set to constant density (as i already wrote)

please any other ideas?

[siara817]

Does the solid part cover all the liquid? I mean if the liquid will have connection with air, then you need to add a phase for air. Other than this, your solid phase is located in an environment, like air then you need to have some air environment around the solid part. Then the solid part will give off the heat to the air and whole system will cool down.

[cwl]

I guess natural outer convection can be modeled by setting arbitrary outer temperture and heat-exchange coefficient - this could prove the corectness of the model; also - take a closer look at Fluid-Solid Interface surface (In-Place this time i guess) it might be incorrect.