modelHumidifier_u

Ideal humidifier or dehumidifier with prescribed water mass flow rate addition or subtraction

Extends from AixLib.Fluid.Interfaces.TwoPortHeatMassExchanger (Partial model transporting one fluid stream with storing mass or energy).

Information

Model for an air humidifier or dehumidifier.

This model adds (or removes) moisture from the air stream. The amount of exchanged moisture is equal to

ṁ_wat = u ṁ_wat,nom,

where u is the control input signal and ṁ_wat,nom is equal to the parameter mWat_flow_nominal. The parameter mWat_flow_nominal can be positive or negative. If ṁ_wat is positive, then moisture is added to the air stream, otherwise it is removed.

If the heat port heatPort is unconnected, then the enthalpy of the air that flows through the device remains unchanged, e.g., the humidification is adiabatic. To change the enthalpy of the air, add heat flow to the connector heatPort.

Parameters

Type	Name	Default	Description
Boolean	homotopyInitialization (from TwoPortHeatMassExchanger)	true	= true, use homotopy method
Modelica.Units.SI.MassFlowRate	mWat_flow_nominal		Water mass flow rate at u=1, positive for humidification
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)
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 › Nominal condition
Modelica.Units.SI.Time	tau (from TwoPortHeatMassExchanger)	30	Time constant at nominal flow (if energyDynamics <> SteadyState)
Dynamics › Conservation equations
Modelica.Fluid.Types.Dynamics	energyDynamics (from TwoPortHeatMassExchanger)	Modelica.Fluid.Types.Dynamics.DynamicFreeInitial	Type of energy balance: dynamic (3 initialization options) or steady state
Initialization
Medium.AbsolutePressure	p_start (from TwoPortHeatMassExchanger)	Medium.p_default	Start value of pressure
Medium.Temperature	T_start (from TwoPortHeatMassExchanger)	Medium.T_default	Start value of temperature
Medium.MassFraction[Medium.nX]	X_start (from TwoPortHeatMassExchanger)	Medium.X_default	Start value of mass fractions m_i/m
Medium.ExtraProperty[Medium.nC]	C_start (from TwoPortHeatMassExchanger)	fill(0, Medium.nC)	Start value of trace substances

Connectors

Type	Name	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	u	Control input
Modelica.Blocks.Interfaces.RealOutput	mWat_flow	Water added to the fluid
Modelica.Thermal.HeatTransfer.Interfaces.HeatPort_a	heatPort	Heat port for total heat exchange with the control volume

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
AixLib.Fluid.MixingVolumes.MixingVolume	vol (from TwoPortHeatMassExchanger)
AixLib.Fluid.FixedResistances.PressureDrop	preDro (from TwoPortHeatMassExchanger)		Flow resistance

Revisions

February 9, 2023, by Michael Wetter:
Removed access to parameter use_T_in which does not exist in this model.
This is for #1697.
March 7, 2022, by Michael Wetter:
Removed massDynamics.
This is for #1542.
April 12, 2017, by Michael Wetter:
Removed parameters use_T_in and T. This removes the optional specification of temperature through the parameter T or the input connector T_in. Exposed the heat port of the control volume to allow adding heat, for example, to use the model as a steam humidifier.
This is for issue Buildings #704.
May 6, 2015, by Michael Wetter:
Set prescribedHeatFlowRate=true. This is for issue #412.
May 29, 2014, by Michael Wetter:
Removed undesirable annotation Evaluate=true.
February 11, 2014 by Michael Wetter:
Corrected issue #197 which led to twice the amount of latent heat being added to the fluid stream.
October 14, 2013 by Michael Wetter:
Constrained medium to be a subclass of Modelica.Media.Interfaces.PartialCondensingGases, as this base class declares the function enthalpyOfCondensingGas.
July 30, 2013 by Michael Wetter:
Updated model to use new variable mWat_flow in the base class.
May 24, 2011, by Michael Wetter:
Changed base class to allow using the model as a dynamic or a steady-state model.
April 14, 2010, by Michael Wetter:
Converted temperature input to a conditional connector.
April 17, 2008, by Michael Wetter:
First implementation.