Function patchMassFlow is included in file controlDict. Definition of forces functions are created in file flux.fun. This function is part of libsimpleFunctionObjects.so library and can evaluate mass flow rate through selected patches:

 massFlowInlet
{
    type                    patchMassFlow;
    region                  spiral;
    functionObjectsLibs     ( "libsimpleFunctionObjects.so" );
    verbose                 true;
    patches
    (
        inflow_inlet
    );
    factor                  1.;
}
massFlowMXP1_spiral
{
    type                    patchMassFlow;
    region                  spiral;
    functionObjectsLibs     ( "libsimpleFunctionObjects.so" );
    verbose                 true;
    patches
    (
        spiral_rotor_mxp_0 spiral_rotor_mxp_1 spiral_rotor_mxp_2 spiral_rotor_mxp_3
        spiral_rotor_mxp_4 spiral_rotor_mxp_5 spiral_rotor_mxp_6 spiral_rotor_mxp_7
    );
    factor                  1.;
}
massFlowMXP1_rotor
{
    type                    patchMassFlow;
    region                  rotor;
    functionObjectsLibs     ( "libsimpleFunctionObjects.so" );
    verbose                 true;
    patches
    (
        rotor_spiral_mxp_0 rotor_spiral_mxp_1 rotor_spiral_mxp_2 rotor_spiral_mxp_3
        rotor_spiral_mxp_4 rotor_spiral_mxp_5 rotor_spiral_mxp_6 rotor_spiral_mxp_7
    );
    factor                  1.;
}
massFlowMXP2_rotor
{
    type                    patchMassFlow;
    region                  rotor;
    functionObjectsLibs     ( "libsimpleFunctionObjects.so" );
    verbose                 true;
    patches
    (
        rotor_drafttube_mxp_0 rotor_drafttube_mxp_1 rotor_drafttube_mxp_2 rotor_drafttube_mxp_3
        rotor_drafttube_mxp_4 rotor_drafttube_mxp_5 rotor_drafttube_mxp_6 rotor_drafttube_mxp_7
    );
    factor                  1.;
}
massFlowMXP2_drafttube
{
    type                    patchMassFlow;
    region                  drafttube;
    functionObjectsLibs     ( "libsimpleFunctionObjects.so" );
    verbose                 true;
    patches
    (
        drafttube_rotor_mxp_0 drafttube_rotor_mxp_1 drafttube_rotor_mxp_2 drafttube_rotor_mxp_3
        drafttube_rotor_mxp_4 drafttube_rotor_mxp_5 drafttube_rotor_mxp_6 drafttube_rotor_mxp_7
    );
    factor                  1.;
}
massFlowOutlet
{
    type                    patchMassFlow;
    region                  drafttube;
    functionObjectsLibs     ( "libsimpleFunctionObjects.so" );
    verbose                 true;
    patches
    (
        outflow_outlet
    );
    factor                  1.;
}

During the computation the results are written down in directory
patchMassFlows_massFlowInlet/0/massFlow,
patchMassFlows_massFlowMXP1_spiral/0/massFlow, …