Nusselt numbers for fully developed laminar flow

Danro

Hi, I am using StarCCM+ to calculate the Nusselt numbers and friction factors for fully developed laminar flow. I chose the steady state, constant density, stationary, laminar, segregated fluid temperature physical model for a 3D (round) pipe, which is subjected to a constant temperature boundary. The Nusselt number is suppose to be 3.66 once the flow is developed, but the results shows that the Nusselt number starts at the inlet with a value of 132 and then continuously decreases up to a value of 2.1 at the outlet. I get the same result even if I make the pipe longer. I would be very thankful if anyone can help me! Thank you!