modelPipeAutosize

Pipe model parameterized with pressure drop per pipe length

Extends from Buildings.Fluid.FixedResistances.PressureDrop.

Information

This model is similar to Buildings.Fluid.FixedResistances.HydraulicDiameter except for the modifications below which allow to use this model for computing the hydraulic diameter at initialization, based on the pressure drop per pipe length at nominal flow rate.

  • The parameter v_nominal is computed based on the nominal flow rate.
  • The equation dp_nominal = fac*dpStraightPipe_nominal is solved at initialization for the hydraulic diameter dh.
  • The parameter dp_nominal is assigned a value that does not need to be computed at initialization. This is required per Modelica specification because the structural parameter computeFlowResistance depends on dp_nominal and must be evaluated at compile time.

Parameters

TypeNameDefaultDescription
Modelica.Units.SI.LengthdhHydraulic diameter (assuming a round cross section area)
Realdp_length_nominal250Pressure drop per pipe length at nominal flow rate
Modelica.Units.SI.LengthlengthLength of the pipe
RealReC4000Reynolds number where transition to turbulence starts
Modelica.Units.SI.Lengthroughness2.5e-5Absolute roughness of pipe, with a default for a smooth steel pipe (PE100: 7E-6)
Realfac2Factor to take into account resistance of bends etc., fac=dp_nominal/dpStraightPipe_nominal
Modelica.Units.SI.PressureDifferencedpStraightPipe_nominalModelica.Fluid.Pipes.BaseClasses.WallFriction.Detailed.pressureLoss_m_flow(m_flow = m_flow_nominal, rho_a = rho_default, rho_b = rho_default, mu_a = mu_default, mu_b = mu_default, length = length, diameter = dh, roughness = roughness, m_flow_small = m_flow_small)Pressure loss of a straight pipe at m_flow_nominal

Components

TypeNameDefaultDescription
Modelica.Units.SI.Velocityvm_flow/(rho_default*ARound)Flow velocity (assuming a round cross section area)

Revisions

  • November 18, 2022, by David Blum:
    start attribute for parameter dh changed to 0.01.
    min attribute for parameter dh changed to 0.001.
    This is for issue 2510.
  • February 23, 2021, by Antoine Gautier:
    First implementation.