modelMixingVolumeMoistAir
Mixing volume with heat port for latent heat exchange, to be used if moisture is added or removed
Extends from Buildings.Fluid.MixingVolumes.BaseClasses.PartialMixingVolume (Partial mixing volume with inlet and outlet ports (flow reversal is allowed)).
Information
Model for an ideally mixed fluid volume and the ability to store mass and energy. The volume is fixed, and latent and sensible heat can be exchanged.
This model represents the same physics as
Buildings.Fluid.MixingVolumes.MixingVolume, but in addition, it allows
adding or subtracting water to the control volume.
The mass flow rate of the added or subtracted water is
specified at the port mWat_flow.
Adding mWat_flow itself does not affect the energy balance
in this model. Hence, the enthalpy that is added or removed with the
flow of mWat_flow needs to be added to the heat port
heatPort.
To increase the numerical robustness of the model, the constant
prescribedHeatFlowRate can be set by the user.
This constant only has an effect if the model has exactly two fluid ports connected,
and if it is used as a steady-state model.
Use the following settings:
- Set
prescribedHeatFlowRate=trueif the only means of heat transfer at theheatPortis a prescribed heat flow rate that is not a function of the temperature difference between the medium and an ambient temperature. Examples include an ideal electrical heater, a pump that rejects heat into the fluid stream, or a chiller that removes heat based on a performance curve. If theheatPortis not connected, then setprescribedHeatFlowRate=trueas in this case,heatPort.Q_flow=0. - Set
prescribedHeatFlowRate=falseif there is heat flow at theheatPortcomputed as K * (T-heatPort.T), for some temperature T and some conductance K, which may itself be a function of temperature or mass flow rate.
If there is a combination of K * (T-heatPort.T) and a prescribed heat flow rate, for example a solar collector that dissipates heat to the ambient and receives heat from the solar radiation, then setprescribedHeatFlowRate=false.
Options
The parameter mSenFac can be used to increase the thermal mass of this model
without increasing its volume. This way, species concentrations are still calculated
correctly even though the thermal mass increases. The additional thermal mass is calculated
based on the density and the value of the function HeatCapacityCp
of the medium state state_default.
This parameter can for instance be useful in a pipe model when the developer wants to
lump the pipe thermal mass to the fluid volume. By default mSenFac = 1, hence
the mass is unchanged. For higher values of mSenFac, the mass will be scaled proportionally.
Set the parameter use_C_flow = true to enable an input connector for the trace substance flow rate.
This allows to directly add or subtract trace substances such as
CO2 to the volume.
See
Buildings.Fluid.Sensors.Examples.PPM
for an example.
Parameters
| Type | Name | Default | Description |
|---|---|---|---|
| Boolean | prescribedHeatFlowRate (from PartialMixingVolume) | false | Set to true if the model has a prescribed heat flow at its heatPort. If the heat flow rate at the heatPort is only based on temperature difference, then set to false |
| Boolean | simplify_mWat_flow (from PartialMixingVolume) | true | Set to true to cause port_a.m_flow + port_b.m_flow = 0 even if mWat_flow is non-zero |
| Modelica.Units.SI.Volume | V (from PartialMixingVolume) | Volume | |
| Dynamics › Conservation equations | |||
| Modelica.Fluid.Types.Dynamics | energyDynamics (from LumpedVolumeDeclarations) | Modelica.Fluid.Types.Dynamics.DynamicFreeInitial | Type of energy balance: dynamic (3 initialization options) or steady state |
| Modelica.Fluid.Types.Dynamics | substanceDynamics (from LumpedVolumeDeclarations) | energyDynamics | Type of independent mass fraction balance: dynamic (3 initialization options) or steady state |
| Modelica.Fluid.Types.Dynamics | traceDynamics (from LumpedVolumeDeclarations) | energyDynamics | Type of trace substance balance: dynamic (3 initialization options) or steady state |
| Advanced › Dynamics | |||
| Modelica.Fluid.Types.Dynamics | massDynamics (from LumpedVolumeDeclarations) | energyDynamics | Type of mass balance: dynamic (3 initialization options) or steady state, must be steady state if energyDynamics is steady state |
| Initialization | |||
| Medium.AbsolutePressure | p_start (from LumpedVolumeDeclarations) | Medium.p_default | Start value of pressure |
| Medium.Temperature | T_start (from LumpedVolumeDeclarations) | Medium.T_default | Start value of temperature |
| Medium.MassFraction[Medium.nX] | X_start (from LumpedVolumeDeclarations) | Medium.X_default | Start value of mass fractions m_i/m |
| Medium.ExtraProperty[Medium.nC] | C_start (from LumpedVolumeDeclarations) | fill(0, Medium.nC) | Start value of trace substances |
| Medium.ExtraProperty[Medium.nC] | C_nominal (from LumpedVolumeDeclarations) | fill(1E-2, Medium.nC) | Nominal value of trace substances. (Set to typical order of magnitude.) |
| Dynamics | |||
| Real | mSenFac (from LumpedVolumeDeclarations) | 1 | Factor for scaling the sensible thermal mass of the volume |
| Advanced | |||
| Boolean | initialize_p (from PartialMixingVolume) | not Medium.singleState | = true to set up initial equations for pressure |
| Modelica.Units.SI.MassFlowRate | m_flow_small (from PartialMixingVolume) | 1E-4*abs(m_flow_nominal) | Small mass flow rate for regularization of zero flow |
| Boolean | use_C_flow | false | Set to true to enable input connector for trace substance |
| Nominal condition | |||
| Modelica.Units.SI.MassFlowRate | m_flow_nominal (from PartialMixingVolume) | Nominal mass flow rate | |
| General › Ports | |||
| Integer | nPorts (from PartialMixingVolume) | 0 | Number of ports |
| Assumptions | |||
| Boolean | allowFlowReversal (from PartialMixingVolume) | true | = false to simplify equations, assuming, but not enforcing, no flow reversal. Used only if model has two ports. |
Connectors
| Type | Name | Default | Description |
|---|---|---|---|
| Modelica.Fluid.Vessels.BaseClasses.VesselFluidPorts_b[nPorts] | ports (from PartialMixingVolume) | Fluid inlets and outlets | |
| Modelica.Blocks.Interfaces.RealOutput | U (from PartialMixingVolume) | Internal energy of the component | |
| Modelica.Blocks.Interfaces.RealOutput | m (from PartialMixingVolume) | Mass of the component | |
| Modelica.Blocks.Interfaces.RealOutput[Medium.nXi] | mXi (from PartialMixingVolume) | Species mass of the component | |
| Modelica.Blocks.Interfaces.RealOutput[Medium.nC] | mC (from PartialMixingVolume) | Trace substance mass of the component | |
| Modelica.Blocks.Interfaces.RealInput | mWat_flow | Water flow rate added into the medium | |
| Modelica.Blocks.Interfaces.RealOutput | X_w | Species composition of medium | |
| Modelica.Thermal.HeatTransfer.Interfaces.HeatPort_a | heatPort | Heat port for sensible plus latent heat exchange with the control volume | |
| Modelica.Blocks.Interfaces.RealInput | C_flow | Trace substance mass flow rate added to the medium |
Components
| Type | Name | Default | Description |
|---|---|---|---|
| Medium.Temperature | T (from PartialMixingVolume) | Medium.temperature_phX(p = p, h = hOut_internal, X = if Medium.reducedX then cat(1, Xi, {1 - sum(Xi)}) else Xi) | Temperature of the fluid |
| Modelica.Units.SI.Pressure | p (from PartialMixingVolume) | if nPorts > 0 then ports[1].p else p_start | Pressure of the fluid |
| Modelica.Units.SI.MassFraction[Medium.nXi] | Xi (from PartialMixingVolume) | XiOut_internal | Species concentration of the fluid |
| Medium.ExtraProperty[Medium.nC] | C (from PartialMixingVolume) | COut_internal | Trace substance mixture content |
Revisions
-
October 19, 2017, by Michael Wetter:
Setinitialize_ptofinalso that it does not appear as a user-selectable parameter. This is done becauseinitialize_phas been changed from aconstantto aparameterfor Buildings, issue 1013. -
April 11, 2017, by Michael Wetter:
Changed comment of heat port, as this needs to be the total heat flow rate in order to be able to use this model for modeling steam humidifiers and adiabatic humidifiers.
Removed blocksQSen_flowandQLat_flow.
This is for issue Buildings #704. -
January 22, 2016 by Michael Wetter:
Removed assignment ofsensibleOnlyinsteBalas this constant is no longer used. -
January 19, 2016, by Michael Wetter:
Updated documentation due to the addition of an input for trace substance in the mixing volume. This is for issue 372. -
February 11, 2014 by Michael Wetter:
Redesigned implementation of latent and sensible heat flow rates as port of the correction of issue #197. -
December 18, 2013 by Michael Wetter:
Changed computation ofsto allow this model to also be used withBuildings.Media.Water. -
October 21, 2013 by Michael Wetter:
Removed dublicate declaration of medium model. -
September 27, 2013 by Michael Wetter:
Reformulated assignment ofi_wto avoid a warning in OpenModelica. -
September 17, 2013 by Michael Wetter:
Changed model to no longer use the obsolete modelBuildings.Fluid.MixingVolumes.BaseClasses.PartialMixingVolumeWaterPort. -
July 30, 2013 by Michael Wetter:
Changed connectormXi_flow[Medium.nXi]to a scalar input connectormWat_flowin the conservation equation model. The reason is thatmXi_flowdoes not allow to compute the other components inmX_flowand therefore leads to an ambiguous use of the model. By only requestingmWat_flow, the mass balance and species balance can be implemented correctly. -
April 18, 2013 by Michael Wetter:
Removed the use of the deprecatedcardinalityfunction. Therefore, all input signals must be connected. -
February 7, 2012 by Michael Wetter:
Revised base classes for conservation equations inBuildings.Fluid.Interfaces. -
February 22, by Michael Wetter:
Improved the code that searches for the index of 'water' in the medium model. -
May 29, 2010 by Michael Wetter:
Rewrote computation of index of water substance. For the old formulation, Dymola 7.4 failed to differentiate the model when trying to reduce the index of the DAE. -
August 7, 2008 by Michael Wetter:
First implementation.