Heat transfer coefficient of the surface

Yves · Posts: 29

Hi,

I'd like to model a large hall with a floor-cooling system (in order to take advantage from the stratification within the room), so I set the floor temperature to 20°C as a boundary condition, and cool air (16°C) supplies close to the floor.
The other boundary temperatures (walls and ceiling) are over 30°C (imported from an E+ simulation)

The problem is I end up with relatively high temperatures (around 27°C) very close to the floor, whereas I expected to have cool air at least in the first meter.

I have the impression that the boundary condition doesn't really affect the simulation, so I thought maybe the problem is that the heat transfer coefficient is too low to allow for surface exchange. Where is this parameter set?

I would also like to know the resulting heat flux through the surface, where can I see this in the cfd results?

Regards,

Yves

Steve Potter · Posts: 614 Location: newcastle

Hi Yves,

You can enter your own surface heat transfer coefficients for walls, floors and ceilings by switching the Surface heat transfer option to 2-User-defined under the Surface heat transfer header on the CFD Calculation Options dialog.

However, the program calculated surface heat transfer coefficients should be reasonably accurate and so I would suggest that you check that you have used the same convective boundary conditions for the E+ simulation as you have specified for the CFD calculation.

Unfortunately, you cannot currently obtain numerical data for surface heat flux from the CFD results.

Regards,

Steve

Yves · Posts: 29

Thank you very much for the information.

Actually for the E+ simulation I had set the floor to adiabatic, because the hall is quite large so the temperature of the ground should remain close to that of the inside air. But of course when I change the temperature of the floor to 20°C in order to model a water-cooled floor, it should no longer be considered as adiabatic. Is the "adiabatic" parameter in the construction>adjacency tab also used for the CFD calculation? This could be the origin of the problem...

Steve Potter · Posts: 614 Location: newcastle

No, the CFD calculation only imports the surface temperature and does not take the adiabatic property into account.

Using the boundary conditions that you state (walls and ceiling > 30C and floor=20C) and if the flow is purely buoyancy driven (no forced convection) you should see clear stratification. However, you mention air supplies close to the floor and these may be causing air mixing which would diminish stratification.

Steve

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