[Arttis]

Hello!

My simulation involves a turbulent water flow in an inclined rectangular cavity:

inlet velocity = 0.003 m/s
Pressure outlet = Patm
Top plate heat flux imposed (different for every simulation, q= 100-1000 W/m2)
Bottom plate and side walls adiabatic, q=0 W/m2

Water is flowing between the plates in a cavity.

When I take an Area Weighted Average value for convective heat transfer coefficient (htc) between the Top surface and the water, I get the same value despite the heat flux applied.

I think htc should change when I change heat flux value, because the temperature varies along the Top surface.

However, in my case, for the constant velocity (and hence the mass flow rate) the heat transfer coefficient remains the same.

Could anyone see what is wrong here? Any help is appreciated.

[Arttis]

Please, could someone help me with this.

[LuckyTran]

The heat transfer coefficient is a property of the flow. If you change only the heat flux and nothing else, then the heat transfer coefficient should not change.

[Arttis]

Originally Posted by LuckyTran

The heat transfer coefficient is a property of the flow. If you change only the heat flux and nothing else, then the heat transfer coefficient should not change.

But the top plate's and water temperature becomes different when a different heat flux is applied.

I don't understand why heat transfer coefficient was changing when I tested the natural convection flow. Instead of velocity-inlet I then had a pressure-inlet boundary condition. Considering that q=h*A*(Ts-Tf), h should not change in natural convection flow either, should it?

[LuckyTran]

Originally Posted by Arttis

But the top plate's and water temperature becomes different when a different heat flux is applied.

I don't understand why heat transfer coefficient was changing when I tested the natural convection flow. Instead of velocity-inlet I then had a pressure-inlet boundary condition. Considering that q=h*A*(Ts-Tf), h should not change in natural convection flow either, should it?

If the flow does not change, when the heat flux changes the temperature change together so that the heat transfer coefficient stays the same.

In natural convection, the density changes due to temperature change and hence buoyancy force changes. In this situation, the flow changes.

[Arttis]

Originally Posted by LuckyTran

If the flow does not change, when the heat flux changes the temperature change together so that the heat transfer coefficient stays the same.

In natural convection, the density changes due to temperature change and hence buoyancy force changes. In this situation, the flow changes.

Thank you, that makes more sense now.