[jpina]

Dear all,

when setting the wall boundary condition it is possible to choose between:

- Convective heat transfer. Where the necessary input is the Heat Transfer Coefficient and the Free Stream Temperature

- Fixed temperature. Where the input is the temperature of the wall.

My question is: Which is the difference between the two options?

When consulting the documentation in:

https://www.sharcnet.ca/Software/Ans...ll_calc_temp_s

At the sections:
6.3.14.11.1. Temperature Boundary Conditions




6.3.14.11.3. Convective Heat Transfer Boundary Conditions

The equation looks the same in both cases.

Thanks a lot!

[Bruno Machado]

Originally Posted by jpina

Dear all,

when setting the wall boundary condition it is possible to choose between:

- Convective heat transfer. Where the necessary input is the Heat Transfer Coefficient and the Free Stream Temperature

- Fixed temperature. Where the input is the temperature of the wall.

My question is: Which is the difference between the two options?

When consulting the documentation in:

https://www.sharcnet.ca/Software/Ans...ll_calc_temp_s

At the sections:
6.3.14.11.1. Temperature Boundary Conditions




6.3.14.11.3. Convective Heat Transfer Boundary Conditions

The equation looks the same in both cases.

Thanks a lot!

In my understanding, the main difference is that for the convective heat transfer BC the wall is assumed to be zero-thickness whilst in the Temperature BC you might have (or not) a solid region.

[LuckyTran]

When you apply a convective heat transfer coefficient as a boundary condition, you are applying an external heat transfer coefficient. The first part of the equation is the, the heat transfer coefficient from the wall to the fluid. But in the convective case, you are equation that heat flux with the external convection. So you have to pay attention to the second line hext (instead of hf).

Originally Posted by jpina

- Convective heat transfer. Where the necessary input is the Heat Transfer Coefficient and the Free Stream Temperature

This is true if you are doing a heat conduction simulation in a solid only. For a fluid simulation you are specifying the external heat transfer coefficient and an external reference temperature. The heat transfer coefficient on the fluid side is computed using the reference temperature specified in the reference values.

[jpina]

Thanks LuckyTran,

moreover, with Fixed Temperature, the temperature of the wall is fixed to the input value. With Convective Heat Transfer the temperature of the wall changes during the simulation.

Am I right?

[LuckyTran]

Originally Posted by jpina

Thanks LuckyTran,

moreover, with Fixed Temperature, the temperature of the wall is fixed to the input value. With Convective Heat Transfer the temperature of the wall changes during the simulation.

Am I right?

Correct. The wall temperature is the temperature needed to satisfy the energy balance of internal and external convection.