determine convective thermal resistance in Steady State Thermal ANSYS

[aliex]

i try to determine convective thermal resistance (R_conv) at different diameters of channels in Steady State Thermal ANSYS , but did not work so far.

because if i define the channel as 3rd boundary condition (convection), i have to define the temperature and heat transfer coefficient h, what i actually do is that i indirectly determine convective thermal resistance, which is wrong.

With CFX I have already worked, I have varied the diameter and got different h and convective thermal resistance (R_conv).

Are there any suggestions on how to determine convective thermal resistance (R_conv) by varying the diameter in Steady State Thermal ANSYS?

Thank you