modelEvaporatorCondenser

Evaporator or condenser with refrigerant experiencing constant temperature phase change

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

Information

Model for a constant temperature evaporator or condenser based on a ε-NTU heat exchanger model.

The heat exchanger effectiveness is calculated from the number of transfer units (NTU):

ε = 1 - exp(- UA ⁄ (ṁ c_p))

Optionally, this model can have a flow resistance. If no flow resistance is requested, set dp_nominal=0.

Limitations

This model does not consider any superheating or supercooling on the refrigerant side. The refrigerant is considered to exchange heat at a constant temperature throughout the heat exchanger.

Parameters

Type	Name	Default	Description
Boolean	homotopyInitialization (from TwoPortHeatMassExchanger)	true	= true, use homotopy method
Modelica.Units.SI.ThermalConductance	UA		Thermal conductance of heat exchanger
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
Modelica.Units.SI.ThermalConductance	UA_small	UA/10	Small thermal conductance for regularisation of heat transfer
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 (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.RealOutput	Q_flow	Heat added to the fluid
Modelica.Blocks.Interfaces.RealOutput	T	Medium temperature
Modelica.Thermal.HeatTransfer.Interfaces.HeatPort_a	port_ref	Temperature and heat flow from the refrigerant

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 (from TwoPortHeatMassExchanger)
Buildings.Fluid.FixedResistances.PressureDrop	preDro (from TwoPortHeatMassExchanger)		Flow resistance
Modelica.Units.SI.Efficiency	NTU	UA/(Buildings.Utilities.Math.Functions.smoothMax(abs(port_a.m_flow), m_flow_small, m_flow_small)*cp_default)	Number of transfer units of heat exchanger
Modelica.Units.SI.Efficiency	eps	Buildings.Utilities.Math.Functions.smoothMin(Buildings.Fluid.HeatExchangers.BaseClasses.epsilon_ntuZ(NTU, 0, Integer(Buildings.Fluid.Types.HeatExchangerFlowRegime.ConstantTemperaturePhaseChange)), 0.999, 1.0e-4)	Effectiveness of heat exchanger
Modelica.Blocks.Sources.RealExpression	UAeff		Effective heat transfer coefficient

Revisions

March 7, 2022, by Michael Wetter:
Removed massDynamics.
This is for #1542.
May 27, 2017, by Filip Jorissen:
Regularised heat transfer around zero flow.
This is for #769.
April 12, 2017, by Michael Wetter:
Corrected invalid syntax for computing the specific heat capacity.
This is for #707.
October 11, 2016, by Massimo Cimmino:
First implementation.