For specific components (armatures, fittings, pipe sections, grids, ...), the zeta value is often given in the data sheet.
Together with a given (or calculated) reference area A, the pressure drop can be calculated:
dp := zeta/(2*rho) * m_flow^2/A^2
The square of the mass-flow is regularized using the Modelica.Fluid.Utilities.regSquare function.
function zetaPressureLoss extends Internal.FlowResistance.partialPressureLoss; input Real zeta(unit = "1") "Zeta value of component" annotation( Dialog(enable = true)); input Boolean fromGeometry = true "Calculate reference area from geometry inputs?" annotation( Dialog(enable = true)); input SI.Area A = Modelica.Constants.pi*r*r "Custom reference area for dp calculation" annotation( Dialog(enable = not fromGeometry)); end zetaPressureLoss;