Reply To: Roughness constant

[Rob]

I'd not expect the roughness to do too much, so won't explain a factor of 1.8 on pressure. The physics should be OK too, but, is the thicker material a Newtonian fluid? Is there a thermal effect that could result in a lower viscosity in the nozzle in reality, but isn't included in the CFD model? How does the surface tension change between the two materials?