SimpleGenericOrificeSimple generic orifice defined by pressure loss coefficient and diameter (only for flow from port_a to port_b) |
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Information
This information is part of the Modelica Standard Library maintained by the Modelica Association.
This pressure drop component defines a simple, generic orifice, where the loss factor ζ is provided for one flow direction (e.g., from loss table of a book):
Δp = 0.5*ζ*ρ*v*|v|
= 8*ζ/(π^2*D^4*ρ) * m_flow*|m_flow|
where
- Δp is the pressure drop: Δp = port_a.p - port_b.p
- D is the diameter of the orifice at the position where ζ is defined (either at port_a or port_b). If the orifice has not a circular cross section, D = 4*A/P, where A is the cross section area and P is the wetted perimeter.
- ζ is the loss factor with respect to D
that depends on the geometry of
the orifice. In the turbulent flow regime, it is assumed that
ζ is constant.
For small mass flow rates, the flow is laminar and is approximated by a polynomial that has a finite derivative for m_flow=0. - v is the mean velocity.
- ρ is the upstream density.
Since the pressure loss factor zeta is provided only for a mass flow from port_a to port_b, the pressure loss is not correct when the flow is reversing. If reversing flow only occurs in a short time interval, this is most likely uncritical. If significant reversing flow can appear, this component should not be used.
Parameters (14)
| dp_start |
Value: dp_nominal Type: AbsolutePressure (Pa) Description: Guess value of dp = port_a.p - port_b.p |
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| m_flow_small |
Value: if system.use_eps_Re then system.eps_m_flow * m_flow_nominal else system.m_flow_small Type: MassFlowRate (kg/s) Description: Small mass flow rate for regularization of zero flow |
| show_T |
Value: true Type: Boolean Description: = true, if temperatures at port_a and port_b are computed |
| show_V_flow |
Value: true Type: Boolean Description: = true, if volume flow rate at inflowing port is computed |
| allowFlowReversal |
Value: system.allowFlowReversal Type: Boolean Description: = true to allow flow reversal, false restricts to design direction (m_flow >= 0) |
| momentumDynamics |
Value: Types.Dynamics.SteadyState Type: Dynamics Description: Formulation of momentum balance |
| m_flow_start |
Value: system.m_flow_start Type: MassFlowRate (kg/s) Description: Start value of mass flow rates |
| diameter |
Value: Type: Diameter (m) Description: Diameter of orifice |
| zeta |
Value: Type: Real Description: Loss factor for flow of port_a -> port_b |
| use_zeta |
Value: true Type: Boolean Description: = false to obtain zeta from dp_nominal and m_flow_nominal |
| m_flow_nominal |
Value: if system.use_eps_Re then system.m_flow_nominal else 1e2 * system.m_flow_small Type: MassFlowRate (kg/s) Description: Mass flow rate for dp_nominal |
| dp_nominal |
Value: if not system.use_eps_Re then 1e3 else BaseClasses.lossConstant_D_zeta(diameter, zeta) / Medium.density_pTX(Medium.p_default, Medium.T_default, Medium.X_default) * m_flow_nominal ^ 2 Type: Pressure (Pa) Description: Nominal pressure drop |
| use_Re |
Value: system.use_eps_Re Type: Boolean Description: = true, if turbulent region is defined by Re, otherwise by m_flow_small |
| from_dp |
Value: true Type: Boolean Description: = true, use m_flow = f(dp) else dp = f(m_flow) |
Inputs (1)
| pathLength |
Default Value: 0 Type: Length (m) Description: Length flow path |
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Connectors (2)
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port_a |
Type: FluidPort_a Description: Fluid connector a (positive design flow direction is from port_a to port_b) |
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port_b |
Type: FluidPort_b Description: Fluid connector b (positive design flow direction is from port_a to port_b) |
Components (3)
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state_a |
Type: ThermodynamicState Description: state for medium inflowing through port_a |
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state_b |
Type: ThermodynamicState Description: state for medium inflowing through port_b |
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system |
Type: System Description: System properties |
Used in Examples (1)
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Modelica.Fluid.Examples Demonstrates the parameterization of a pump and a pipe for given nominal values |