Pessure Drop Incorrectly Decreases When Volume Fraction Increases
 

Hello,

I am running a Fluent simulation (laminar flow) with water as phase 1 and aluminum-oxide as phase 2. I have selected Eulerian multiphase approach and have defined the parameters of phase 2 as such.

My geometry is 2D and I have selected the axisymmetric condition. Pipe radius is 10 mm and length is 1 m. Inlet velocity is 0.01 m/s.

I have ran simulations at 1 through 5% volume fraction of aluminum oxide. When I increase volume fraction, my ansys simulation reports a decrease in pressure drop, which we know should not be the case. I have shared some images of pressure contours.

I have compared the velocity profile with the analytical velocity profile and there is very close agreement. The temperature profile and heat transfer coefficient all agree with expectation (both increase as VF increases), so it seems I am doing *most* of the simulation correctly, however the pressure drop is something that I am stuck on.

Can anyone offer any help or pointers?