modelTwoPortHeatMassExchanger

Partial model transporting one fluid stream with storing mass or energy

Extends from Buildings.Fluid.Interfaces.PartialTwoPortInterface (Partial model with two ports and declaration of quantities that are used by many models), Buildings.Fluid.Interfaces.TwoPortFlowResistanceParameters (Parameters for flow resistance for models with two ports).

Information

This component transports one fluid stream. It provides the basic model for implementing dynamic and steady-state models that exchange heat and water vapor with the fluid stream. The model also computes the pressure drop due to the flow resistance. By setting the parameter dp_nominal=0, the computation of the pressure drop can be avoided. The variable vol.heatPort.T always has the value of the temperature of the medium that leaves the component. For the actual temperatures at the port, the variables sta_a.T and sta_b.T can be used. These two variables are provided by the base class Buildings.Fluid.Interfaces.PartialTwoPortInterface.

For models that extend this model, see for example

June 17, 2026, by Michael Wetter:
Updated implementation to allow a flow coefficient n that is different from 2. This allows use of the model for not fully turbulent flow.
This is for Buildings, #4620.
the ideal heater or cooler Buildings.Fluid.HeatExchangers.HeaterCooler_u, and
the ideal humidifier Buildings.Fluid.Humidifiers.Humidifier_u.

Implementation

The variable names follow the conventions used in Modelica.Fluid.Examples.HeatExchanger.BaseClasses.BasicHX .

Parameters

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

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.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
Buildings.Fluid.MixingVolumes.MixingVolume	vol
Buildings.Fluid.FixedResistances.PressureDrop	preDro		Flow resistance

Revisions

March 3, 2022, by Michael Wetter:
Removed massDynamics.
This is for issue 1542.
April 14, 2020, by Michael Wetter:
Changed homotopyInitialization to a constant.
This is for IBPSA, #1341.
December 1, 2016, by Michael Wetter:
Updated model as use_dh is no longer a parameter in the pressure drop model.
This is for #480.
January 26, 2016, by Michael Wetter:
Added final quantity=Medium.substanceNames for X_start.
May 6, 2015, by Michael Wetter:
Added missing propagation of allowFlowReversal to instance vol. This is for issue #412.
May 1, 2015, by Marcus Fuchs:
Fixed links in documentation.
October 6, 2014, by Michael Wetter:
Changed medium declaration in pressure drop element to be final.
May 28, 2014, by Michael Wetter:
Removed annotation(Evaluate=true) for parameter tau. This is needed to allow changing the time constant after translation.
November 12, 2013, by Michael Wetter:
Removed import Modelica.Constants statement.
October 8, 2013, by Michael Wetter:
Removed parameter show_V_flow.
December 14, 2012 by Michael Wetter:
Renamed protected parameters for consistency with the naming conventions.
October 17, 2012, by Michael Wetter:
Fixed broken link in documentation.
February 3, 2012, by Michael Wetter:
Removed assignment of m_flow_small as it is no longer used in the pressure drop model.
January 15, 2011, by Michael Wetter:
Fixed wrong class reference in information section.
September 13, 2011, by Michael Wetter:
Changed assignment of vol(mass/energyDynamics=...) as the previous assignment caused a non-literal start value that was ignored.
July 29, 2011, by Michael Wetter:
Added start value for outflowing enthalpy.
July 11, 2011, by Michael Wetter:
Changed parameterization of fluid volume so that steady-state balance is used when tau = 0.
May 25, 2011, by Michael Wetter:
Removed temperature sensor and changed implementation of fluid volume to allow use of this model for the steady-state and dynamic humidifier Buildings.Fluid.MassExchangers.HumidifierPrescribed.
March 25, 2011, by Michael Wetter:
Added homotopy operator.
March 21, 2010 by Michael Wetter:
Changed pressure start value from system.p_start to Medium.p_default since HVAC models may have water and air, which are typically at different pressures.
April 13, 2009, by Michael Wetter:
Added model to compute flow friction.
January 29, 2009 by Michael Wetter:
First implementation.