modelOrifice
Orifice
Extends from Annex60.Airflow.Multizone.BaseClasses.PowerLawResistance (Flow resistance that uses the power law).
Information
This model describes the mass flow rate and pressure difference relation of an orifice in the form
V_flow = k * dp^m,
where k is a variable and
m a parameter. For turbulent flow, set m=1/2 and
for laminar flow, set m=1.
Large openings are characterized by values close to 0.5,
while values near 0.65 have been found for small
crack-like openings (Dols and Walton, 2002).
References
- W. Stuart Dols and George N. Walton, CONTAMW 2.0 User Manual, Multizone Airflow and Contaminant Transport Analysis Software, Building and Fire Research Laboratory, National Institute of Standards and Technology, Tech. Report NISTIR 6921, November, 2002.
Parameters
| Type | Name | Default | Description |
|---|---|---|---|
| Boolean | forceErrorControlOnFlow (from ErrorControl) | true | Flag to force error control on m_flow. Set to true if interested in flow rate |
| Modelica.SIunits.Area | A (from PowerLawResistance) | |Orifice characteristics|Area of orifice | |
| Real | m (from PowerLawResistance) | Flow exponent, m=0.5 for turbulent, m=1 for laminar | |
| Boolean | useDefaultProperties (from PowerLawResistance) | true | Set to false to use density and viscosity based on actual medium state, rather than using default values |
| Modelica.SIunits.PressureDifference | dp_turbulent (from PowerLawResistance) | 0.1 | Pressure difference where laminar and turbulent flow relation coincide. Recommended = 0.1 |
| Modelica.SIunits.Length | lWet (from PowerLawResistance) | sqrt(A) | Wetted perimeter used for Reynolds number calculation |
| Real | CD | 0.65 | |Orifice characteristics|Discharge coefficient |
| Assumptions | |||
| Boolean | allowFlowReversal (from PartialTwoPort) | true | = false to simplify equations, assuming, but not enforcing, no flow reversal |
| Nominal condition | |||
| Modelica.SIunits.MassFlowRate | m_flow_nominal (from PartialTwoPortInterface) | Nominal mass flow rate | |
| Advanced | |||
| Modelica.SIunits.MassFlowRate | m_flow_small (from PartialTwoPortInterface) | 1E-4*abs(m_flow_nominal) | Small mass flow rate for regularization of zero flow |
| Boolean | homotopyInitialization (from PowerLawResistance) | true | = true, use homotopy method |
| Advanced › Diagnostics | |||
| Boolean | show_T (from PartialTwoPortInterface) | false | = true, if actual temperature at port is computed |
Connectors
| Type | Name | Default | Description |
|---|---|---|---|
| Modelica.Fluid.Interfaces.FluidPort_a | port_a (from PartialTwoPort) | Fluid connector a (positive design flow direction is from port_a to port_b) | |
| Modelica.Fluid.Interfaces.FluidPort_b | port_b (from PartialTwoPort) | Fluid connector b (positive design flow direction is from port_a to port_b) |
Components
| Type | Name | Default | Description |
|---|---|---|---|
| Modelica.SIunits.MassFlowRate | m_flow (from PartialTwoPortInterface) | port_a.m_flow | Mass flow rate from port_a to port_b (m_flow > 0 is design flow direction) |
| Modelica.SIunits.PressureDifference | dp (from PartialTwoPortInterface) | port_a.p - port_b.p | Pressure difference between port_a and port_b |
| Medium.ThermodynamicState | sta_a (from PartialTwoPortInterface) | Medium.setState_phX(port_a.p, noEvent(actualStream(port_a.h_outflow)), noEvent(actualStream(port_a.Xi_outflow))) | Medium properties in port_a |
| Medium.ThermodynamicState | sta_b (from PartialTwoPortInterface) | Medium.setState_phX(port_b.p, noEvent(actualStream(port_b.h_outflow)), noEvent(actualStream(port_b.Xi_outflow))) | Medium properties in port_b |
| Modelica.SIunits.VolumeFlowRate | V_flow (from PowerLawResistance) | Volume flow rate through the component | |
| Modelica.SIunits.Velocity | v (from PowerLawResistance) | Average velocity | |
| Modelica.SIunits.Density | rho (from PowerLawResistance) | Fluid density at port_a | |
| Real | Re (from PowerLawResistance) | Reynolds number |
Revisions
-
October 8, 2013 by Michael Wetter:
Changed the parameteruseConstantDensitytouseDefaultPropertiesto use consistent names within this package. A conversion script can be used to update this parameter. -
December 6, 2011 by Michael Wetter:
Replacedrhowithrho_nominalbecauserhois computed in anequationsection and not in theinitial equationsection. -
July 20, 2010 by Michael Wetter:
Migrated model to Modelica 3.1 and integrated it into the Buildings library. -
February 4, 2005 by Michael Wetter:
Released first version.