CFD Online Discussion Forums - Pressure drop in packed bed

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Pressure drop in packed bed

All,

I am trying to investigate the pressure drop in a cylindrical column, packed with 50 spheres. I know the inlet pressure (150 psi, or 1149 m2/s2 with SG 0.9), and I know the outlet flow rate (20 kg/hr). I have been using simpleFoam, defining inlet pressure and outlet flow. However, after trying a bunch of inlet/outlet combinations, I cannot get a reasonable solution to my problem. An image of my system has been attached.

My pressure boundary file is below, followed by my velocity.

Any tips are appreciated!

Quote:

FoamFile
{
version 2.0;
format ascii;
class volScalarField;
object p;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

dimensions [0 2 -2 0 0 0 0];

internalField uniform 1149.13;

boundaryField
{
Inlet
{
type fixedValue;
value uniform 1149.13;
}

Outlet
{
type fixedValue;
value $internalField;
}

Walls
{
type zeroGradient;
}

Balls
{
type zeroGradient;
}
defaultFaces
{
type empty;
}

}

Quote:

FoamFile
{
version 2.0;
format ascii;
class volVectorField;
object U;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

dimensions [0 1 -1 0 0 0 0];

internalField uniform (0 0 0.001947);

boundaryField
{
Inlet
{
type fixedValue;
value $internalField;
}

Outlet
{
type flowRateInletVelocity;
massFlowRate constant 0.005;
rho rho;
rhoInlet 900;
value uniform (0 0 0);

// type inletOutlet;
// inletValue uniform (0 0 0.001947);
// value uniform (0 0 0.001947);
}

Walls
{
type fixedValue;
value uniform (0 0 0);
}

Balls
{
type fixedValue;
value uniform (0 0 0);
}
defaultFaces
{
type empty;
}

}

For simpleFOAM, generally you want to specify p at the outlet (usually 0) and specify the velocity (or mass flow) at the inlet. For your case try:

P:
internalField uniform 0;
Inlet
{
type zeroGradient;
}
Outlet
{
type fixedValue;
value $internalField;
}

U:
Inlet
{ //what you listed for outlet:
type flowRateInletVelocity;
massFlowRate constant 0.005;
rho rho;
rhoInlet 900;
//type fixedValue; //or you can use fixedValue instead of the above
value uniform (0 0 0.001947);
}
Outlet
{
type zeroGradient;
}

Run it and see if the pressure at the inlet matches up to the value you expect, 150 psi

Also, your geometry looks like it might be a challenge to mesh. Where the spheres contact each other might result in non-orthogonal or poor quality cells. That would make it difficult to converge a solution.

Hope that helps.