modelSprayAirWasher_X
Extends from Buildings.Fluid.HeatExchangers.BaseClasses.PartialPrescribedOutlet (Ideal heater, cooler, humidifier or dehumidifier with prescribed outlet conditions).
Information
Model for a spray air washer with a prescribed outlet water vapor mass fraction in kg/kg total air.
This model forces the outlet water mass fraction at port_b to be
no lower than the
input signal X_wSet, subject to optional limits on the
maximum water vapor mass flow rate that is added, as
described by the parameter mWatMax_flow.
By default, the model has unlimited capacity.
The output signal mWat_flow ≥ 0 is the moisture added
to the medium if the flow rate is from port_a to port_b.
If the flow is reversed, then mWat_flow = 0.
The outlet specific enthalpy at port_b is increased by
the enthalpy of liquid water at 10°C times the mass of water that was added.
Therefore, the temperature of the leaving fluid is below the inlet temperature.
The outlet conditions at port_a are not affected by this model,
other than for a possible pressure difference due to flow friction.
If the parameter energyDynamics is different from
Modelica.Fluid.Types.Dynamics.SteadyState,
the component models the dynamic response using a first order differential equation.
The time constant of the component is equal to the parameter tau.
This time constant is adjusted based on the mass flow rate using
τeff = τ |ṁ| ⁄ ṁnom
where τeff is the effective time constant for the given mass flow rate ṁ and τ is the time constant at the nominal mass flow rate ṁnom. This type of dynamics is equal to the dynamics that a completely mixed control volume would have.
Optionally, this model can have a flow resistance.
Set dp_nominal = 0 to disable the flow friction calculation.
For a model that uses a control signal u ∈ [0, 1] and multiplies this with the nominal water mass flow rate, use Buildings.Fluid.Humidifiers.Humidifier_u
Limitations
This model only adds water vapor for the flow from
port_a to port_b.
The water vapor of the reverse flow is not affected by this model.
This model does not affect the enthalpy of the air. Therefore, if water is added, the temperature will decrease, e.g., the humidification is adiabatic.
Parameters
| Type | Name | Default | Description |
|---|---|---|---|
| Boolean | homotopyInitialization (from PartialPrescribedOutlet) | true | = true, use homotopy method |
| Modelica.Units.SI.MassFlowRate | mWatMax_flow | Modelica.Constants.inf | Maximum water mass flow rate addition (positive) |
| Assumptions | |||
| Boolean | allowFlowReversal (from PartialTwoPort) | true | = false to simplify equations, assuming, but not enforcing, no flow reversal |
| Nominal condition | |||
| Modelica.Units.SI.MassFlowRate | m_flow_nominal (from PartialTwoPortInterface) | Nominal mass flow rate | |
| Modelica.Units.SI.PressureDifference | dp_nominal (from TwoPortFlowResistanceParameters) | Pressure difference | |
| Advanced | |||
| Modelica.Units.SI.MassFlowRate | m_flow_small (from PartialTwoPortInterface) | 1E-4*abs(m_flow_nominal) | Small mass flow rate for regularization of zero flow |
| Advanced › Diagnostics | |||
| Boolean | show_T (from PartialTwoPortInterface) | false | = true, if actual temperature at port is computed |
| Flow resistance | |||
| Boolean | computeFlowResistance (from TwoPortFlowResistanceParameters) | true | =true, compute flow resistance. Set to false to assume no friction |
| Boolean | from_dp (from TwoPortFlowResistanceParameters) | false | = true, use m_flow = f(dp) else dp = f(m_flow) |
| Real | n (from TwoPortFlowResistanceParameters) | 2 | Flow exponent, n=1 for laminar, n=2 for turbulent |
| Boolean | linearizeFlowResistance (from TwoPortFlowResistanceParameters) | false | = true, use linear relation between m_flow and dp for any flow rate |
| Real | deltaM (from TwoPortFlowResistanceParameters) | 0.1 | Fraction of nominal flow rate where flow transitions to laminar |
| Dynamics › Conservation equations | |||
| Modelica.Fluid.Types.Dynamics | energyDynamics (from PartialPrescribedOutlet) | Modelica.Fluid.Types.Dynamics.SteadyState | Type of energy balance: dynamic (3 initialization options) or steady state |
| Dynamics | |||
| Modelica.Units.SI.Time | tau (from PartialPrescribedOutlet) | 10 | Time constant at nominal flow rate (used if energyDynamics not equal Modelica.Fluid.Types.Dynamics.SteadyState) |
| Initialization | |||
| Modelica.Units.SI.MassFraction[Medium.nX] | X_start | Medium.X_default | Start value of mass fractions m_i/m |
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) | |
| Modelica.Blocks.Interfaces.RealInput | X_w | Set point for water vapor mass fraction in kg/kg total air of the fluid that leaves port_b | |
| Modelica.Blocks.Interfaces.RealOutput | mWat_flow | Water added to the fluid (if flow is from port_a to port_b) |
Components
| Type | Name | Default | Description |
|---|---|---|---|
| Modelica.Units.SI.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.Units.SI.PressureDifference | dp (from PartialTwoPortInterface) | port_a.p - port_b.p | Pressure difference between port_a and port_b |
| Medium.ThermodynamicState | sta_a (from PartialTwoPortInterface) | if allowFlowReversal then Medium.setState_phX(port_a.p, noEvent(actualStream(port_a.h_outflow)), noEvent(actualStream(port_a.Xi_outflow))) else Medium.setState_phX(port_a.p, noEvent(inStream(port_a.h_outflow)), noEvent(inStream(port_a.Xi_outflow))) | Medium properties in port_a |
| Medium.ThermodynamicState | sta_b (from PartialTwoPortInterface) | if allowFlowReversal then Medium.setState_phX(port_b.p, noEvent(actualStream(port_b.h_outflow)), noEvent(actualStream(port_b.Xi_outflow))) else Medium.setState_phX(port_b.p, noEvent(port_b.h_outflow), noEvent(port_b.Xi_outflow)) | Medium properties in port_b |
Revisions
-
March 8, 2022, by Michael Wetter:
Renamed parametermassDynamicstoenergyDynamicsfor consistency with other models. -
December 14, 2018, by Michael Wetter:
Restricted base class for medium to one that implements the functionenthalpyOfLiquid.
This is for #1057. -
May 3, 2017, by Michael Wetter:
First implementation.