modelEffectiveAirLeakageArea
Effective air leakage area
Extends from Annex60.Airflow.Multizone.Orifice (Orifice).
Information
This model describes the one-directional pressure driven air flow through a crack-like opening.
The opening is modeled as an orifice. The orifice area is parameterized by processing the effective air leakage area, the discharge coefficient and pressure drop at a reference condition. The effective air leakage area can be obtained, for example, from the ASHRAE fundamentals (ASHRAE, 1997, p. 25.18). In the ASHRAE fundamentals, the effective air leakage area is based on a reference pressure difference of 4 Pa and a discharge coefficient of 1. A similar model is also used in the CONTAM software (Dols and Walton, 2002). Dols and Walton (2002) recommend to use for the flow exponent m=0.6 to m=0.7 if the flow exponent is not reported with the test results.
References
- ASHRAE, 1997. ASHRAE Fundamentals, American Society of Heating, Refrigeration and Air-Conditioning Engineers, 1997.
- Dols and Walton, 2002. 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 (from Orifice) | 0.65 | |Orifice characteristics|Discharge coefficient |
| Modelica.SIunits.PressureDifference | dpRat | 4 | |Rating conditions|Pressure drop at rating condition |
| Real | CDRat | 1 | |Rating conditions|Discharge coefficient |
| Modelica.SIunits.Area | L | Effective leakage area | |
| 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
-
January 22, 2016, by Michael Wetter:
Corrected type declaration of pressure difference. This is for #404. -
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. -
July 20, 2010 by Michael Wetter:
Migrated model to Modelica 3.1 and integrated it into the Buildings library. -
February 10, 2005 by Michael Wetter:
Released first version.