modelMBeva

Counter current Moving Boundary model: Fluid enters subcooled and exits in super-heated conditons. The model consider the fluid in one side and the metal wall. The secondary fluid is a constant specfic heat fluid

▶ Check in your browser

Information

Model MBeva is a moving boundaries heat exchanger model for evaporators. The model considers a fictitius heat transfer channel split up into three different section based on the phase state of the working fluid:

Sub-cooled zone (SB)
Two-phase zone (TP)
SuperHeated zone (SH)

Pressure and enthalpy are selected as state variables for each of the three zones.

The name moving boundary is derived from the fact that the interfaces between these sections do not have a fixed spatial position but merely a fixed thermodynamic location depending on the presence of liquid and gaseous fluid, respectively. The actual existence of a certain section and its length are determined based on the fluid state resulting in variable sectioning. A fixed total length superimposes the required boundary condition to calculate the length of each section.

The assumptions for this model are:

The tube is cylindrical with a constant cross sectional area
The velocity of the fluid is uniform on the cross sectional area
The enthalpy of the fluid is linear in each region of the tube (sub-cooled, two-phase, super-heated)
Pressure is considered constant
Constant void fraction
Thermal energy accumulation in the metal wall is taken into account
The secondary fluid is treated as a constant heat capacity fluid
The heat transfer between the secondary fluid and the metal wall and between the metal wall and the primary fluid is computed using the epsilon-NTU method

Parameters

Type	Name	Default	Description
Modelica.SIunits.Area	A		Cross-sectional area for both side of the heat exchanger
Modelica.SIunits.Length	L		Total length of the exchanger
Modelica.SIunits.Length	D	2*sqrt(A/pi)	Diameter
Real	pi	Modelica.Constants.pi
Modelica.SIunits.Mass	M_tot		Total mass of metal walll between the fluids
Modelica.SIunits.SpecificHeatCapacity	c_wall		Heat capacity of the wall - assumed constant in the whole heat exchanger
Modelica.SIunits.Density	rho_wall		Density of the wall - assumed constant in the whole heat exchanger
Modelica.SIunits.Temperature	dTsf_start	10	\|Initialization\|Temperature change
Modelica.SIunits.Temperature	Tsf_SU_start	273.15 + 25	\|Initialization\|Temperature inlet
Modelica.SIunits.CoefficientOfHeatTransfer	U_SB		Heat transfer coefficient sub-cooled side
Modelica.SIunits.CoefficientOfHeatTransfer	U_TP		Heat transfer coefficient two-phase side
Modelica.SIunits.CoefficientOfHeatTransfer	U_SH		Heat transfer coefficient Superheated side
Modelica.SIunits.CoefficientOfHeatTransfer	Usf		Secondary fluid Heat transfer coefficient sub-cooled side
Modelica.SIunits.QualityFactor	ETA	1	Fin efficiency
Real	Void		Void fraction assumed constant for now
Real	dVoid_dp	0	Void fraction derivative with respect to pressure
Real	dVoid_dh	0	Void fraction derivative with respect to enthalpy

Connectors

Type	Name	Default	Description
ThermoCycle.Interfaces.Fluid.FlangeA	InFlow
ThermoCycle.Interfaces.Fluid.FlangeB	OutFlow
ThermoCycle.Interfaces.Fluid.Flange_ex_Cdot	OutFlow_sf
ThermoCycle.Interfaces.Fluid.Flange_Cdot	InFlow_sf

Components

Type	Name	Description
Medium.ThermodynamicState	SubCooled	Subcooled thermodynamic state
Medium.SaturationProperties	sat
Medium.ThermodynamicState	SuperHeated	Superheated thermodynamic state
Medium.ThermodynamicState	outlet	Outlet thermodynamic state
Modelica.SIunits.Pressure	p	Pressure in the heat-exchanger: No pressure drop considered
Modelica.SIunits.MassFlowRate	M_dot_su	Mass flow at the inlet of the heat exchanger
Modelica.SIunits.MassFlowRate	M_dot_A	Mass flow at the interface between sub-cooled and two-phase
Modelica.SIunits.MassFlowRate	M_dot_B	Mass flow at the interface between sub-cooled and two-phase
Modelica.SIunits.MassFlowRate	M_dot_ex	Mass flow at the outlet of the heat exchanger
Modelica.SIunits.MassFlowRate	Mdot_sf	Mass flow of the secondary fluid of the heat exchanger
Modelica.SIunits.Power	Q_SB	Thermal energy transfer with the wall
Modelica.SIunits.Power	Q_TP	Thermal energy transfer with the wall in the two-phase region
Modelica.SIunits.Power	Q_SH	Thermal energy transfer with the wall in the superheated region
Modelica.SIunits.Power	Q_tot	Total Thermal energy transfer with the wall from the primary fluid
Modelica.SIunits.Power	Q_tot_sf	Total Thermal energy transfer with the wall from the secondary fluid
Modelica.SIunits.Power	Qsf_SH
Modelica.SIunits.Power	Qsf_TP
Modelica.SIunits.Power	Qsf_SB
Modelica.SIunits.Temperature	T_SU	Temperatue at the inlet of the heat exchanger
Modelica.SIunits.Temperature	T_SB	Mean Temperatue of the subcooled region
Modelica.SIunits.Temperature	T_TP	Mean Temperatue of the two-phase region
Modelica.SIunits.Temperature	T_SH	Mean Temperatue of the superheated region
Modelica.SIunits.Temperature	TwA	Wall Temperature at the interface between sub-cooled and two-phase
Modelica.SIunits.Temperature	TwB	Wall Temperature at the interface between two-phase and super-heated
Modelica.SIunits.Temperature	T_out	Temperature at the outlet of the moving boundary model
Modelica.SIunits.Temperature	TwSB	Mean Wall temperature in the sub-cooled region
Modelica.SIunits.Temperature	TwTP	Mean Wall Temperature in the two-phase region
Modelica.SIunits.Temperature	TwSH	Mean Wall Temperature in the super-heated region
Modelica.SIunits.Temperature	Tsf_SU	Tempearture at the inlet of the secondary fluid
Modelica.SIunits.Temperature	Tsf_SH	Mean Temperatue of the superheated region secondary fluid
Modelica.SIunits.Temperature	Tsf_B	Secondary fluid temperature at the interface between two-phase and super-heated
Modelica.SIunits.Temperature	Tsf_TP	Mean Temperatue of the two-phase region secondary fluid
Modelica.SIunits.Temperature	Tsf_A	Secondary fluid temperature at the interface between two-phase and super-heated
Modelica.SIunits.Temperature	Tsf_SB	Mean Temperatue of the subcooled region secondary fluid
Modelica.SIunits.Temperature	Tsf_EX	Secondary fluid temperature at the exit of the heat exchanger
Modelica.SIunits.Length	L_SB	Length of the subcooled region
Modelica.SIunits.Length	L_TP	Length of the two-phase region
Modelica.SIunits.Length	L_SH	Length of the Superheated region
Modelica.SIunits.Density	rho_SB	Mean density of the subcooled region
Modelica.SIunits.Density	rho_LS	Bubble density
Modelica.SIunits.Density	rho_VS	Dew density
Modelica.SIunits.Density	rho_TP	Mean density of the two-phase region
Modelica.SIunits.Density	rho_SH	Mean density of the superheated region
Modelica.SIunits.Density	rho_sf	Density of the secondary fluid at the inlet
Modelica.SIunits.SpecificHeatCapacity	cp_sf	Specific heat capacity of the secondary fluid at the inlet
Modelica.SIunits.SpecificHeatCapacity	cp_SB	Specific heat capacity of the secondary fluid at the inlet
Modelica.SIunits.SpecificHeatCapacity	cp_TP	Specific heat capacity of the secondary fluid at the inlet
Modelica.SIunits.SpecificHeatCapacity	cp_SH	Specific heat capacity of the secondary fluid at the inlet
Modelica.SIunits.SpecificEnthalpy	h_SB	Mean Enthalpy of the subcooled region
Modelica.SIunits.SpecificEnthalpy	h_LS	Bubble enthalpy
Modelica.SIunits.SpecificEnthalpy	h_VS	Dew enthalpy
Modelica.SIunits.SpecificEnthalpy	h_SH	Mean Enthalpy of the Superheated region
Modelica.SIunits.SpecificEnthalpy	h_SU	Enthalpy at the inlet of the heat exchanger of the primary fluid
Modelica.SIunits.SpecificEnthalpy	h_EX	Enthalpy at the outlet of the heat exchanger of the primary fluid
Real	rhoh_TP	Density times enthalpy in the two-phase region
Modelica.SIunits.DerDensityByEnthalpy	drdh_SB	Density derivative with respect to enthalpy at constant pressure in the subcooled region
Modelica.SIunits.DerDensityByPressure	drdp_SB	Density derivative with respect to pressure at constant enthalpy in the subcooled region
Modelica.SIunits.DerDensityByPressure	drdp_LS	Bubble point density derivative with respect to pressure
Modelica.SIunits.DerDensityByPressure	drdp_VS	Dew point density derivative with respect to pressure
Modelica.SIunits.DerDensityByEnthalpy	drdh_SH	Density derivative with respect to enthalpy at constant pressure in the superheated region
Modelica.SIunits.DerDensityByPressure	drdp_SH	Density derivative with respect to pressure at constant enthalpy in the superheated region
Modelica.SIunits.DerEnthalpyByPressure	dhdp_LS	Bubble point specific enthalpy derivative with respect to pressure
Modelica.SIunits.DerEnthalpyByPressure	dhdp_VS	Dew point specific enthalpy derivative with respect to pressure
Real	drdt_SB	Density derivative with respect to time in the subcooled region
Real	dhdt_SB	Enthalpy derivative with respect to time in the subcooled region
Real	drdt_TP	Density derivative with respect to time in the two-phase region
Real	drhdt_TP	Density and Enthalpy derivative with respect to time in the two-phase region
Real	drdt_SH	Density derivative with respect to time in the superheated region
Real	dhdt_SH	Enthalpy derivative with respect to time in the superheated region
Real	epsilon_SB_sf	Epsilon Sub-cooled secondary fluid - wall Side
Real	NTU_SB_sf	NTU Sub-cooled secondary fluid-Wall side
Real	epsilon_TP_sf	Epsilon Two-Phase secondary fluid - wall Side
Real	NTU_TP_sf	NTU Two-Phase secondary fluid-Wall side
Real	epsilon_SH_sf	Epsilon Super-heated secondary fluid - wall Side
Real	NTU_SH_sf	NTU Super-heated secondary fluid-Wall side
Real	epsilon_SB_pf	Epsilon Sub-cooled wall side - primary fluid
Real	NTU_SB_pf	NTU Sub-cooled wall side - primary fluid
Real	epsilon_TP_pf	Epsilon Two-Phase wall side - primary fluid
Real	NTU_TP_pf	NTU Two-Phase wall side - primary fluid
Real	epsilon_SH_pf	Epsilon Super-heated wall side - primary fluid
Real	NTU_SH_pf	NTU Super-heated secondary wall side - primary fluid
SummaryClass	Summary

Name	Description
Medium
SummaryBase
SummaryClass

modelMBeva

Information

Parameters

Connectors

Components

Contents