modelExhaustHeatExchanger

Exhaust gas heat exchanger for engine combustion and its heat transfer to a cooling circle

Extends from AixLib.Fluid.Interfaces.PartialFourPortInterface (Partial model with four ports and declaration of quantities that are used by many models).

Information

Overview

Exhaust gas heat exchanger for engine combustion and its heat transfer to a cooling circle.

Assumptions

The convective heat transfer between exhaust gas and heat exchanger is calculated as a cylindrical exhaust pipe. For the pipe cross-section, the connection cross-section of the power unit is used; the heat transfer area and the capacity of the heat exchanger can be calibrated.

Known variables are the combustion air ratio and the heat flow to the cooling water circuit at nominal operation. These are used to estimate the pipe diameters if unknown.

The heat transfer to the environment (G_Amb) and the cooling water circuit (G_Cool) is calculated by means of heat conduction.

There is the option of considering the heat output from the condensation of water in the flue gas. This is determined from the determination of the precipitating water via the saturation vapour pressure and the critical loading in the flue gas for the critical state (at outlet temperature). The evaporation enthalpy is approximated using an empirical formula based on table data for ambient pressure.

Simplifying it is assumed that the latent heat flux in addition to the convective heat flux is transferred to the capacity of the exhaust gas heat exchanger.

April, 2019 by Julian Matthes:
First implementation (see issue #667)

Parameters

Type	Name	Default	Description
Modelica.Units.SI.MolarMass	M_H2O	0.01802	Molar mass of water
Real	A	11.7621
Real	B	3874.61
Real	C	229.73
Assumptions
Boolean	allowFlowReversal1 (from PartialFourPort)	true	= false to simplify equations, assuming, but not enforcing, no flow reversal for medium 1
Boolean	allowFlowReversal2 (from PartialFourPort)	true	= false to simplify equations, assuming, but not enforcing, no flow reversal for medium 2
Nominal condition
Modelica.Units.SI.MassFlowRate	m1_flow_nominal (from PartialFourPortInterface)		Nominal mass flow rate
Modelica.Units.SI.MassFlowRate	m2_flow_nominal (from PartialFourPortInterface)		Nominal mass flow rate
Modelica.Units.SI.Length	d_iExh	CHPEngData.dExh	Inner diameter of exhaust pipe
Modelica.Units.SI.PressureDifference	dp_CooExhHex	CHPEngData.dp_Coo	Pressure drop at nominal mass flow rate inside the coolant circle
Advanced
Medium1.MassFlowRate	m1_flow_small (from PartialFourPortInterface)	1E-4*abs(m1_flow_nominal)	Small mass flow rate for regularization of zero flow
Medium2.MassFlowRate	m2_flow_small (from PartialFourPortInterface)	1E-4*abs(m2_flow_nominal)	Small mass flow rate for regularization of zero flow
Advanced › Diagnostics
Boolean	show_T (from PartialFourPortInterface)	false	= true, if actual temperature at port is computed
Unit properties
AixLib.DataBase.CHP.ModularCHPEngineData.CHPEngDataBaseRecord	CHPEngData	DataBase.CHP.ModularCHPEngineData.CHP_ECPowerXRGI15()	Needed engine data for calculations
Advanced › Sensor Properties
Modelica.Units.SI.Time	tau	1	Time constant of the temperature sensors at nominal flow rate
Modelica.Blocks.Types.Init	initType	Modelica.Blocks.Types.Init.InitialState	Type of initialization (InitialState and InitialOutput are identical)
Boolean	transferHeat	false	If true, temperature T converges towards TAmb when no flow
Modelica.Units.SI.Time	tauHeaTra	1200	Time constant for heat transfer, default 20 minutes
Advanced › Initialization
Modelica.Units.SI.Temperature	T1_start	T_Amb	Initial or guess value of output (= state)
Modelica.Units.SI.Temperature	T2_start	T_Amb	Initial or guess value of output (= state)
Modelica.Media.Interfaces.Types.AbsolutePressure	p1_start	p_Amb	Start value of pressure
Modelica.Media.Interfaces.Types.AbsolutePressure	p2_start	p_Amb	Start value of pressure
Modelica.Media.Interfaces.Types.AbsolutePressure	dp_start	CHPEngData.dp_Coo	Guess value of dp = port_a.p - port_b.p
Modelica.Units.SI.MassFlowRate	m_flow_start	0	Guess value of m_flow = port_a.m_flow
Advanced › Condensing technology
Boolean	ConTec	false	Is condensing technology used and should latent heat be considered?
Ambient Properties
Modelica.Units.SI.Temperature	T_Amb	298.15	Fixed ambient temperature for heat transfer
Modelica.Media.Interfaces.Types.AbsolutePressure	p_Amb	101325	Start value of pressure
Calibration parameters
Modelica.Units.SI.Area	A_surExhHea	50	Surface for exhaust heat transfer
Modelica.Units.SI.ThermalConductance	GAmb	5	Constant thermal conductance of material
Modelica.Units.SI.ThermalConductance	GCoo	850	Constant thermal conductance of material
Modelica.Units.SI.HeatCapacity	CExhHex	4000	Heat capacity of exhaust heat exchanger(default= 4000 J/K)
Calibration parameters › Engine parameters
Modelica.Units.SI.Length	l_ExhHex	1	Length of the exhaust pipe inside the exhaust heat exchanger
Thermal
Modelica.Units.SI.MolarMass	M_Exh	1200	Molar mass of the exhaust gas

Connectors

Type	Name	Description
Modelica.Fluid.Interfaces.FluidPort_a	port_a1 (from PartialFourPort)	Fluid connector a1 (positive design flow direction is from port_a1 to port_b1)
Modelica.Fluid.Interfaces.FluidPort_b	port_b1 (from PartialFourPort)	Fluid connector b1 (positive design flow direction is from port_a1 to port_b1)
Modelica.Fluid.Interfaces.FluidPort_a	port_a2 (from PartialFourPort)	Fluid connector a2 (positive design flow direction is from port_a2 to port_b2)
Modelica.Fluid.Interfaces.FluidPort_b	port_b2 (from PartialFourPort)	Fluid connector b2 (positive design flow direction is from port_a2 to port_b2)
AixLib.Controls.Interfaces.CHPControlBus	cHPExhHexBus	Signal bus of the exhaust gas heat exchanger
Modelica.Thermal.HeatTransfer.Interfaces.HeatPort_a	port_amb	Heat port to ambient

Components

Type	Name	Default	Description
Medium1.MassFlowRate	m1_flow (from PartialFourPortInterface)	port_a1.m_flow	Mass flow rate from port_a1 to port_b1 (m1_flow > 0 is design flow direction)
Modelica.Units.SI.PressureDifference	dp1 (from PartialFourPortInterface)	port_a1.p - port_b1.p	Pressure difference between port_a1 and port_b1
Medium2.MassFlowRate	m2_flow (from PartialFourPortInterface)	port_a2.m_flow	Mass flow rate from port_a2 to port_b2 (m2_flow > 0 is design flow direction)
Modelica.Units.SI.PressureDifference	dp2 (from PartialFourPortInterface)	port_a2.p - port_b2.p	Pressure difference between port_a2 and port_b2
Medium1.ThermodynamicState	sta_a1 (from PartialFourPortInterface)	if allowFlowReversal1 then Medium1.setState_phX(port_a1.p, noEvent(actualStream(port_a1.h_outflow)), noEvent(actualStream(port_a1.Xi_outflow))) else Medium1.setState_phX(port_a1.p, inStream(port_a1.h_outflow), inStream(port_a1.Xi_outflow))	Medium properties in port_a1
Medium1.ThermodynamicState	sta_b1 (from PartialFourPortInterface)	if allowFlowReversal1 then Medium1.setState_phX(port_b1.p, noEvent(actualStream(port_b1.h_outflow)), noEvent(actualStream(port_b1.Xi_outflow))) else Medium1.setState_phX(port_b1.p, port_b1.h_outflow, port_b1.Xi_outflow)	Medium properties in port_b1
Medium2.ThermodynamicState	sta_a2 (from PartialFourPortInterface)	if allowFlowReversal2 then Medium2.setState_phX(port_a2.p, noEvent(actualStream(port_a2.h_outflow)), noEvent(actualStream(port_a2.Xi_outflow))) else Medium2.setState_phX(port_a2.p, inStream(port_a2.h_outflow), inStream(port_a2.Xi_outflow))	Medium properties in port_a2
Medium2.ThermodynamicState	sta_b2 (from PartialFourPortInterface)	if allowFlowReversal2 then Medium2.setState_phX(port_b2.p, noEvent(actualStream(port_b2.h_outflow)), noEvent(actualStream(port_b2.Xi_outflow))) else Medium2.setState_phX(port_b2.p, port_b2.h_outflow, port_b2.Xi_outflow)	Medium properties in port_b2
Real	QuoT_ExhInOut	senTExhHot.T/senTExhCold.T	Quotient of exhaust gas in and outgoing temperature
Real	x_H2OExhDry		Water load of the exhaust gas
Real	xSat_H2OExhDry		Saturation water load of the exhaust gas
Modelica.Units.SI.MassFlowRate	m_H2OExh		Mass flow of water in the exhaust gas
Modelica.Units.SI.MassFlowRate	m_ExhDry		Mass flow of dry exhaust gas
Modelica.Units.SI.MassFlowRate	m_ConH2OExh		Mass flow of condensing water
Modelica.Units.SI.AbsolutePressure	pExh		Pressure in the exhaust gas stream (assuming ambient conditions)
Modelica.Units.SI.AbsolutePressure	pSatH2OExh		Saturation vapor pressure of the exhaust gas water
Modelica.Units.SI.SpecificEnthalpy	deltaH_Vap		Specific enthalpy of vaporization (empirical formula based on table data)
Modelica.Units.SI.SpecificHeatCapacity	meanCpExh	cHPExhHexBus.calMeaCpExh	Calculated specific heat capacity of the exhaust gas for the calculated combustion temperature
Modelica.Units.SI.HeatFlowRate	Q_Gen	cHPExhHexBus.calThePowGen	Calculated loss heat from the induction machine
Modelica.Units.SI.Temperature	T_LogMeanExh		Mean logarithmic temperature of exhaust gas
Medium1.ThermodynamicState	state1	Medium1.setState_pTX(senTExhHot.port_b.p, T_LogMeanExh, senTExhHot.port_b.Xi_outflow)
Modelica.Units.SI.SpecificEnthalpy	h1_in	Medium1.specificEnthalpy(state1)
Modelica.Units.SI.DynamicViscosity	eta1_in	Medium1.dynamicViscosity(state1)
Modelica.Units.SI.Density	rho1_in	Medium1.density_phX(state1.p, h1_in, state1.X)
Modelica.Units.SI.Velocity	v1_in	senMasFloExh.m_flow/(Modelica.Constants.pirho1_ind_iExh^2/4)
Modelica.Units.SI.ThermalConductivity	lambda1_in	Medium1.thermalConductivity(state1)
Modelica.Units.SI.ReynoldsNumber	Re1_in	Modelica.Fluid.Pipes.BaseClasses.CharacteristicNumbers.ReynoldsNumber(v1_in, rho1_in, eta1_in, d_iExh)
Modelica.Blocks.Sources.RealExpression	machineIsOff		Calculated heat from generator losses
AixLib.Utilities.Logical.SmoothSwitch	switch2
Modelica.Blocks.Sources.RealExpression	heatToCooling
Modelica.Blocks.Sources.RealExpression	condensingWater
AixLib.Fluid.Sensors.TemperatureTwoPort	senTExhHot		Temperature sensor of hot side of exhaust heat exchanger
AixLib.Fluid.Sensors.TemperatureTwoPort	senTExhCold		Temperature sensor of cold side of exhaust heat exchanger
AixLib.Fluid.Sensors.MassFlowRate	senMasFloExh		Sensor for mass flwo rate
AixLib.Fluid.Sensors.TemperatureTwoPort	senTCooCold		Temperature sensor of coolant cold side of exhaust heat exchanger
AixLib.Fluid.Sensors.TemperatureTwoPort	senTCooHot		Temperature sensor of coolant hot side of exhaust heat exchanger
AixLib.Fluid.Sensors.MassFlowRate	senMasFloCool		Sensor for mass flwo rate
AixLib.Fluid.FixedResistances.Pipe	pipeCoolant		Pipe model for heat transfer to the cooling circuit
Modelica.Fluid.Vessels.ClosedVolume	volExhaust		Fluid volume of the exhaust gas inside the heat exchanger
AixLib.Fluid.FixedResistances.HydraulicDiameter	pressureDropExhaust		Pressure drop of the exhaust gas
AixLib.Utilities.HeatTransfer.HeatConvPipeInsideDynamic	heatConvExhaustPipeInside		Heat transfer model using convection calculation
Modelica.Thermal.HeatTransfer.Sources.PrescribedHeatFlow	additionalHeat		Heat flow from water condensation in the exhaust gas and generator losses
Modelica.Blocks.Sources.RealExpression	latentAndGeneratorHeat		Calculated latent exhaust heat from water condensation
Modelica.Thermal.HeatTransfer.Components.HeatCapacitor	heatCapacitor		Thermal capacity of the exhaust gas heat exchanger
Modelica.Thermal.HeatTransfer.Components.ThermalConductor	ambientLoss

Name	Description
Medium3
Medium4