Dear All.

I am simulating convective heat transfer by using FLUENT 17.2 in 6 meters circular pipe. Inner diameter of pipe is 14.46 mm. Fluid is water and pipe is copper. mass flow rate is 0.033 kg/s. To reduce the computational effort, I use periodic boundary condition. My simulation seems work for velocity and pressure field. However, distribution of temperature is not good.

Here is the setting:

The Velocity-pressure coupling is SIMPLEC, Gradient: Green-Gauss Node based, Momentum: QUICK, Pressure: Standard, TKE: QUICK, SDR: QUICK, Energy: QUICK.

If the heat transfer has good performance, the temperature gradient must be 0.00166 C/mm (in 20 mm segment should be the temperature different between inlet and outlet is 0.033 C). How to handle this small temperature difference for periodic boundary condition?

Do you have any suggestion?

Best regards