heat transfer in circular tube with constant heat flux

Hi everyone!

in this case
Heat transfer in a circular tube is simualted using Heat Transfer in Fluid interface with temperature as inlet at one end, outlet BC is used at the other end, constant heat flux (150 W/m^2) is specified as B.C. at the wall.
The local total normal heat flux averaged along the perimeter varies from one end to the other.
For example: Normal heat flux from Line Average 1 is found to be -1108.5264509963026 W/m^2,
Normal heat flux from Line Average 4 is found to be -865.521019727185 W/m^2 (see the attached mph file),

Since the constant heat flux is specified at the wall, the total normal heat flux should be close to 150 W/m^2
It appears that the heat flux (genearl inward heat flux) BC only ensure avearge heat flux over the wall equal to 150 W/m^2, but the local heat flux varies.
Is there anybody knows how to ensure that the constant heat flux is satisfied everywhere at the wall?
Basically i want to examine the local Nussel numbe with constant heat flux BC in the circular tube to see if i can get a nusselt number close to the theoretical value 4.364 .

I would be very much appreciated if any one could help with this problem!