Condenser Evaporator (2P-MA)
Models heat exchange between a moist air network and a network that can undergo
phase change
Description
The Condenser Evaporator (2P-MA) block models a heat exchanger with one
moist air network, which flows between ports A2 and
B2, and one two-phase fluid network, which flows between ports
A1 and B1. The heat exchanger can act as a
condenser or as an evaporator. The fluid streams can be aligned in parallel, counter, or
cross-flow configurations.
You can model the moist air side as flow within tubes, flow around the two-phase fluid
tubing, or by an empirical, generic parameterization. The moist air side comprises air,
trace gas, and water vapor that may condense throughout the heat exchange cycle. The
block model accounts for energy transfer from the air to the liquid water condensation
layer. This liquid layer does not collect on the heat transfer surface and is assumed to
be completely removed from the downstream moist air flow. The moisture condensation rate
is returned as a physical signal at port W.
The block uses the Effectiveness-NTU (E-NTU) method to model heat transfer through the
shared wall. Fouling on the exchanger walls, which increases thermal resistance and
reduces the heat exchange between the two fluids, is also modeled. You can also
optionally model fins on both the moist air and two-phase fluid sides. Pressure loss due
to viscous friction on both sides of the exchanger can be modeled analytically or by
generic parameterization, which you can use to tune to your own data.
You can model the two-phase fluid side as flow within a tube or a set of tubes. The
two-phase fluid tubes use a boundary-following model to track the sub-cooled liquid (L),
vapor-liquid mixture (M), and super-heated vapor (V) in three zones. The relative amount
of space a zone occupies in the system is called a zone length
fraction within the system.
The sum of the zone length fractions in the two-phase fluid tubing equals
1
. Port Z returns the zone
length fractions as a vector of physical signals for each of the three phases: [L, M,
V].
Heat Exchanger Configuration
The heat exchanger effectiveness is based on the selected heat exchanger
configuration, the fluid properties in each phase, the tube geometry and flow
configuration on each side of the exchanger, and the usage and size of fins.
Flow ArrangementThe Flow arrangement parameter assigns the relative flow
paths between the two sides:
Parallel flow
indicates the fluids are
moving in the same direction.
Counter flow
indicates the fluids are
moving in parallel, but opposite directions.
Cross flow
indicates the fluids are
moving perpendicular to each other.
Thermal MixingWhen Flow arrangement is set to Cross
flow
, use the Cross flow arrangement
parameter to indicate whether the two-phase fluid or moist air flows are
separated into multiple paths by baffles or walls. Without these separations,
the flow can mix freely and is considered mixed. Both
fluids, one fluid, or neither fluid can be mixed in the cross-flow arrangement.
Mixing homogenizes the fluid temperature along the direction of flow of the
second fluid, and varies perpendicular to the second fluid flow.
Unmixed flows vary in temperature both along and perpendicular to the flow
path of the second fluid.



Note that the flow direction during simulation does not impact the selected
flow arrangement setting. The ports on the block do not reflect the physical
positions of the ports in the physical heat exchange system.
All flow arrangements are single-pass, which means that the fluids do not make
multiple turns in the exchanger for additional points of heat transfer. To model
a multi-pass heat exchanger, you can arrange multiple Condenser Evaporator
(2P-MA) blocks in series or in parallel.
For example, to achieve a two-pass configuration on the two-phase fluid side
and a single-pass configuration on the moist air side, you can connect the
two-phase fluid sides in series and the moist air sides to the same input in
parallel (such as two Mass Flow Rate Source blocks with half of the total mass
flow rate), as shown below.
Flow GeometryThe Flow geometry parameter sets the moist air flow
arrangement as either inside a tube or set of tubes, or perpendicular to a tube
bank. You can also specify an empirical, generic configuration. The two-phase
fluid always flows inside a tube or set of tubes.
When Flow geometry is set to Flow
perpendicular to bank of circular tubes
, use the
Tube bank grid arrangement parameter to define the
two-phase fluid tube bank alignment as either Inline
or Staggered
. The red, downward-pointing arrow
indicates the direction of moist air flow. Also indicated in the Inline figure
are the Number of tube rows along flow direction and the
Number of tube segments in each tube row parameters.
Here, flow direction refers to the moist air flow, and
tube refers to the two-phase fluid tubing. The
Length of each tube segment in a tube row parameter is
indicated in the Staggered figure.


FinsThe heat exchanger configuration is without fins when the Total fin
surface area parameter is set to 0 m^2
. Fins
introduce additional surface area for additional heat transfer. Each fluid side
has a separate fin area.
Effectiveness-NTU Heat Transfer
The heat transfer rate is calculated for each fluid phase. In accordance with the
three fluid zones that occur on the two-phase fluid side of the heat exchanger, the
heat transfer rate is calculated in three sections.
The heat transfer in a zone is calculated as:
where:
CMin is the lesser of the
heat capacity rates of the two fluids in that zone. The heat capacity
rate is the product of the fluid specific heat,
cp, and the fluid mass
flow rate. CMin is always
positive.
TIn,2P is the zone inlet
temperature of the two-phase fluid.
TIn,MA is the zone inlet
temperature of the moist air.
ε is the heat exchanger effectiveness.
Effectiveness is a function of the heat capacity rate and the number
of transfer units, NTU, and also varies based on the heat
exchanger flow arrangement, which is discussed in more detail in Effectiveness by Flow Arrangement. The
NTU is calculated as:
where:
z is the individual zone length fraction.
R is the total thermal resistance between the two
flows, due to convection, conduction, and any fouling on the tube walls:
where:
U is the convective heat transfer
coefficient of the respective fluid. This coefficient is
discussed in more detail in Two-Phase Fluid Correlations and Moist Air Correlations.
F is the Fouling
factor on the two-phase fluid or moist air
side, respectively.
RW is the
Thermal resistance through heat transfer
surface.
ATh is the heat
transfer surface area of the respective side of the
exchanger. ATh is
the sum of the wall surface area,
AW, and the
Total fin surface area,
AF:
where
ηF is the
Fin efficiency.
The total heat transfer rate between the fluids is the sum of the heat transferred
in the three zones by the subcooled liquid
(QL), liquid-vapor mixture
(QM), and superheated vapor
(QV):
Effectiveness by Flow ArrangementThe heat exchanger effectiveness varies according to its flow configuration
and the mixing in each fluid. Below are the formulations for effectiveness
calculated in the liquid and vapor zones for each configuration. The
effectiveness is for all configurations in the mixture zone.
When Flow arrangement is set to
Parallel flow
:
When Flow arrangement is set to
Counter flow
:
When Flow arrangement is set to
Cross flow
and Cross flow
arrangement is set to Both fluids
unmixed
:
When Flow arrangement is set to
Cross flow
and Cross flow
arrangement is set to Both fluids
mixed
:
When one fluid is mixed and the other unmixed, the equation for
effectiveness depends on the relative heat capacity rates of the fluids.
When Flow arrangement is set to Cross
flow
and Cross flow arrangement
is set to either Two-Phase Fluid 1 mixed & Moist Air 2
unmixed
or Two-Phase Fluid 1 unmixed
& Moist Air 2 mixed
:
CR denotes the ratio
between the heat capacity rates of the two fluids:
Condensation
On the moist air side, a layer of condensation may form on the heat transfer
surface. This liquid layer can influence the amount of heat transferred between the
moist air and two-phase fluid. The equations for E-NTU heat transfer above are given
for dry heat transfer. To correct for the influence of
condensation, the E-NTU equations are additionally calculated with the wet
parameters listed below. Whichever of the two calculated heat flow rates results in
a larger amount of moist air side cooling is used in heat calculations for each zone
[1]. To use this method, the Lewis number is assumed to be close to 1 [1], which is
true for moist air.
E-NTU Quantities Used for Heat Transfer Rate Calculations
| Dry calculation | Wet calculation |
---|
Moist air zone inlet temperature | Tin,MA | Tin,wb,MA |
Heat capacity rate | | |
Heat transfer coefficient | UMA | |
where:
Tin,MA is the moist air zone
inlet temperature.
Tin,wb,MA is the moist air
wet-bulb temperature associated with
Tin,MA.
is the dry air mass flow rate.
is the moist air heat capacity per unit mass of dry
air.
is the equivalent heat capacity. The
equivalent heat capacity is the change in the
moist air specific enthalpy (per unit of dry air), , with respect to temperature at saturated moist air conditions:
The mass flow rate of the condensed water vapor leaving the moist air
mass flow depends on the relative humidity between the moist air inlet and the
channel wall and the heat exchanger NTUs:
where:
Wwall,MA is the humidity
ratio at the heat transfer surface.
Win,MA is the humidity ratio
at the moist air flow inlet.
NTUMA is the number of
transfer units on the moist air side, calculated as:
The energy flow associated with water vapor condensation is based on
the difference between the vapor specific enthalpy,
hwater, wall, and the specific
enthalpy of vaporization, hfg, for water:
The condensate is assumed to not accumulate on the heat transfer
surface, and does not influence geometric parameters such as tube diameter. The
condensed water is assumed to be completely removed from the downstream moist air
flow.
Two-Phase Fluid Correlations
Heat Transfer CoefficientThe convective heat transfer coefficient varies according to the fluid Nusselt number:
where:
Nu is the zone mean Nusselt number, which
depends on the flow regime.
k is the fluid phase thermal
conductivity.
DH is tube hydraulic
diameter.
For turbulent flows in the subcooled liquid or superheated vapor zones, the
Nusselt number is calculated with the Gnielinski correlation:
where:
For turbulent flows in the liquid-vapor mixture zone, the Nusselt number is
calculated with the Cavallini-Zecchin correlation:
where:
ReSL is the Reynolds
number of the saturated liquid.
PrSL is the Prandtl
number of the saturated liquid.
ρSL is the density of
the saturated liquid.
ρSV is the density of
the saturated vapor.
a= 0.05, b = 0.8, and
c= 0.33.
For laminar flows, the Nusselt number is set by the Laminar flow
Nusselt number parameter.
For transitional flows, the Nusselt number is a blend between the laminar and
turbulent Nusselt numbers.
Empirical Nusselt Number FormulationWhen the Heat transfer coefficient model parameter is set
to Colburn equation
, the Nusselt number for the
subcooled liquid and superheated vapor zones is calculated by the empirical the
Colburn equation:
where a, b, and
c are defined in the Coefficients [a, b, c] for
a*Re^b*Pr^c in liquid zone and Coefficients [a, b, c]
for a*Re^b*Pr^c in vapor zone parameters.
The Nusselt number for liquid-vapor mixture zones is calculated with the
Cavallini-Zecchin equation, with the variables specified in the
Coefficients [a, b, c] for a*Re^b*Pr^c in mixture zone
parameter.
Pressure LossThe pressure loss due to viscous friction varies depending on flow regime and
configuration. The calculation uses the overall density, which is the total
two-phase fluid mass divided by the total two-phase fluid volume.
For turbulent flows, when the Reynolds number is above the Turbulent
flow lower Reynolds number limit, the pressure loss due to
friction is calculated in terms of the Darcy friction factor. The pressure
differential between port A1 and the internal node I1 is:
where:
A1 is the total flow rate
through port A1.
fD,A is the Darcy
friction factor, according to the Haaland correlation:
where
εR is the two-phase
fluid pipe Internal surface absolute roughness.
Note that the friction factor is dependent on the Reynolds number,
and is calculated at both ports for each liquid.
L is the Total length of each
tube on the two-phase fluid side.
LAdd is the two-phase
fluid side Aggregate equivalent length of local
resistances, which is the equivalent length of a tube
that introduces the same amount of loss as the sum of the losses due
to other local resistances in the tube.
ACS is the tube
cross-sectional area.
The pressure differential between port B1
and internal node I1 is:
where B1 is the total flow rate through port
B1.
The Darcy friction factor at port B1 is:
For laminar flows, when the Reynolds number is below the Laminar
flow upper Reynolds number limit, the pressure loss due to
friction is calculated in terms of the Laminar friction constant for
Darcy friction factor, λ. λ
is a user-defined parameter when Tube cross-section is set
to Generic
, otherwise, the value is calculated
internally. The pressure differential between port A1 and
internal node I1 is:
where μ is the two-phase fluid dynamic viscosity. The
pressure differential between port B1 and internal node I1 is:
For transitional flows, the pressure differential due to viscous friction is a
smoothed blend between the values for laminar and turbulent pressure
losses.
Empirical Pressure Loss FormulationWhen Pressure loss model is set to Pressure
loss coefficient
, the pressure losses due to viscous friction
are calculated with an empirical pressure loss coefficient,
ξ.
The pressure differential between port A1 and internal
node I1 is:
The pressure differential between port
B1 and internal node I1 is:
Moist Air Correlations
Heat Transfer Coefficient for Flows Inside One or More TubesWhen the moist air Flow geometry is set to
Flow inside one or more tubes
, the Nusselt number
is calculated according to the Gnielinski correlation in the same manner as
two-phase supercooled liquid or superheated vapor. See Heat Transfer Coefficient for more
information.
Heat Transfer Coefficient for Flows Across a Tube BankWhen the moist air Flow geometry is set to
Flow perpendicular to bank of circular tubes
, the
Nusselt number is calculated based on the Hagen number, Hg, and depends on the
Tube bank grid arrangement setting:
where:
D is the Tube outer
diameter.
lL is the
Longitudinal tube pitch (along flow
direction), the distance between the tube centers
along the flow direction. Flow direction refers
to the moist air flow.
lT is the
Transverse tube pitch (perpendicular to flow
direction), shown in the figure below. The transverse
pitch is the distance between the centers of the two-phase fluid
tubing in one row.
lD is the diagonal tube
spacing, calculated as
For more information on calculating the Hagen number, see [6].
The longitudinal and transverse pitch distances are the same for both grid
bank arrangement types.


Empirical Nusselt Number ForumulationWhen the Heat transfer coefficient model is set to
Colburn equation
or when Flow
geometry is set to Generic
, the
Nusselt number is calculated by the empirical the Colburn equation:
where a, b, and
c are the values defined in the Coefficients
[a, b, c] for a*Re^b*Pr^c parameter.
Pressure Loss for Flow Inside TubesWhen the moist air Flow geometry is set to
Flow inside one or more tubes
, the pressure loss
is calculated in the same manner as for two-phase flows, with the respective
Darcy friction factor, density, mass flow rates, and pipe lengths of the moist
air side. See Pressure Loss for more
information.
Pressure Loss for Flow Across Tube BanksWhen the moist air Flow geometry is set to
Flow perpendicular to bank of circular tubes
, the
Hagen number is used to calculate the pressure loss due to viscous friction. The
pressure differential between port A2 and internal node I2 is:
where:
The pressure differential between port B2
and internal node I2 is:
Empirical Pressure Loss FormulationWhen the Pressure loss model is set to Euler
number per tube row
or when Flow geometry
is set to Generic
, the pressure loss due to viscous
friction is calculated with a pressure loss coefficient, in terms of the Euler
number, Eu:
where ξ is the empirical pressure loss
coefficient.
The pressure differential between port A2 and internal
node I2 is:
The pressure differential between port
B2 and internal node I2 is:
Conservation Equations
Two-Phase FluidThe total mass accumulation rate in the two-phase fluid is defined as:
where:
M2P is the total mass of
the two-phase fluid.
A1 is the mass flow rate of
the fluid at port A1.
B1 is the mass flow rate of
the fluid at port B1.
The flow is positive when flowing into the block through the
port.
The energy conservation equation relates the change in specific internal
energy to the heat transfer by the fluid:
where:
u2P is the two-phase
fluid specific internal energy.
φA1 is the energy flow
rate at port A1.
φB1 is the energy flow
rate at port B1.
Q is heat transfer rate, which is positive when
leaving the two-phase fluid volume.
Moist AirThere are three equations for mass conservation on the moist air side: one for
the moist air mixture, one for condensed water vapor, and one for the trace gas.
Note
If Trace gas model is set to
None
in the Moist Air
Properties (MA) block, the trace gas is not modeled
in blocks in the moist air network. In the Heat Exchanger
(TL-MA) block, this means that the conservation
equation for trace gas is set to 0.
The moist air mixture mass accumulation rate accounts for the changes of the
entire moist air mass flow through the exchanger ports and the condensation mass
flow rate:
The mass conservation equation for water vapor accounts for the water vapor
transit through the moist air side and condensation formation:
where:
xw is the mass fraction
of the vapor. is the rate of change of this fraction.
is the water vapor mass flow rate at port
A2.
is the water vapor mass flow rate at port
B2.
is the rate of condensation.
The trace gas mass balance is:
where:
xg is the mass fraction
of the trace gas. is the rate of change of this fraction.
is the trace gas mass flow rate at port
A2.
is the trace gas mass flow rate at port
B2.
Energy conservation on the moist air side accounts for the change in specific
internal energy due to heat transfer and water vapor condensing out of the moist
air mass:
where:
ϕA2 is the energy flow
rate at port A2.
ϕB2 is the energy flow
rate at port B2.
ϕCond
is the energy flow rate due to condensation.
The heat transferred to or from the moist air,
Q, is equal to the heat transferred from or to the
two-phase fluid.
Ports
Conserving
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A1
— Two-phase fluid port
two-phase fluid
Inlet or outlet port associated with the two-phase fluid.
B1
— Two-phase fluid port
two-phase fluid
Inlet or outlet port associated with the two-phase fluid.
A2
— Moist air port
moist air
Inlet or outlet port associated with the moist air.
B2
— Moist air port
moist air
Inlet or outlet port associated with the moist air.
Output
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Z
— Two-phase fluid zone length fractions
physical signal
Three-element vector of the zone length fractions in the two-phase
fluid channel, returned as a physical signal. The vector takes the form
[L, M, V], where L is the sub-cooled liquid, M is the liquid-vapor
mixture, and V is the superheated vapor.
W
— Moist air condensation rate
physical signal
Water condensation rate in the moist air flow, returned as a physical
signal. The condensate does not accumulate on the heat transfer
surface.
Parameters
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Configuration
Flow arrangement
— Flow path alignment
Cross flow
(default) | Parallel flow
| Counter flow
Flow path alignment between the heat exchanger sides. The available
flow arrangements are:
Parallel flow
. The flows run in
the same direction.
Counter flow
. The flows run
parallel to each other, in the opposite directions.
Cross flow
. The flows run
perpendicular to each other.
Cross flow arrangement
— Thermal mixing condition
Two-Phase Fluid 1 unmixed & Moist Air
2 mixed
(default) | Both fluids unmixed
| Two-phase fluid 1 mixed & Moist Air 2
unmixed
| Both fluids mixed
Select whether each of the fluids can mix in its channel. Mixed flow
means that the fluid is free to move in the transverse direction as it
travels along the flow path. Unmixed flow means that the fluid is
restricted to travel only along the flow path. For example, a side with
fins is considered an unmixed flow.
Dependencies
To enable this parameter, set Flow
arrangement to Cross
flow
.
Thermal resistance through heat transfer surface
— Wall thermal resistance
0 K/kW
(default) | positive scalar
Thermal resistance of the wall that separates the two sides of the
heat exchanger. The wall thermal resistance, wall fouling, and fluid
convective heat transfer coefficient influence the amount of heat
transferred between the flows.
Cross-sectional area at port A1
— Flow area at port A1
0.01 m^2
(default) | positive scalar
Flow area at the two-phase fluid port A1.
Cross-sectional area at port B1
— Flow area at port B1
0.01 m^2
(default) | positive scalar
Flow area at the two-phase fluid port B1.
Cross-sectional area at port A2
— Flow area at port A2
0.01 m^2
(default) | positive scalar
Flow area at the moist air side port A2.
Cross-sectional area at port B2
— Area normal to flow at port B2
0.01 m^2
(default) | positive scalar
Flow area at the moist air side port B2.
Two-Phase Fluid 1
Number of tubes
— Number of two-phase fluid tubes
25
(default) | positive scalar
Number of two-phase fluid tubes.
Total length of each tube
— Total length of each two-phase fluid tube
1 m
(default) | positive scalar
Total length of each two-phase fluid tube.
Tube cross section
— Cross-sectional shape of a tube
Circular
(default) | Rectangular
| Annular
| Generic
Cross-sectional shape of a tube. Use
Generic
to specify an arbitrary
cross-sectional geometry.
This parameter specifies the cross-section of one tube.
Tube inner diameter
— Internal diameter of a single tube
0.05 m
(default) | positive scalar
Internal diameter of the cross-section of one tube. The cross-section
and diameter are uniform along the tube. The size of the diameter
influences the pressure loss and heat transfer calculations.
Dependencies
To enable this parameter, set Tube
cross-section to
Circular
.
Tube width
— Internal width of a single tube
0.05 m
(default) | positive scalar
Internal width of the cross-section of one tube. The cross-section and
width are uniform along the tube. The width and height influence the
pressure loss and heat transfer calculations.
Dependencies
To enable this parameter, set Tube
cross-section to
Rectangular
.
Tube height
— Internal height of a single tube
0.05 m
(default) | positive scalar
Internal height of one tube. The cross-section and height are uniform
along the tube. The width and height influence the pressure loss and
heat transfer calculations.
Dependencies
To enable this parameter, set Tube
cross-section to
Rectangular
.
Annulus inner diameter (heat transfer surface)
— Smaller diameter of annular cross-section
0.05 m
(default) | positive scalar
Smaller diameter of the annular cross-section of one tube. The
cross-section and inner diameter are uniform along the tube. The inner
diameter influences the pressure loss and heat transfer calculations.
Heat transfer occurs through the inner surface of the annulus.
Dependencies
To enable this parameter, set Tube
cross-section to
Annular
.
Annulus outer diameter
— Larger diameter of annular cross-section
0.1 m
(default) | positive scalar
Larger diameter of the annular cross-section of one tube. The
cross-section and outer diameter are uniform along the tube. The outer
diameter influences the pressure loss and heat transfer
calculations.
Dependencies
To enable this parameter, set Tube
cross-section to
Annular
.
Cross-sectional area per tube
— Internal area normal to flow in a single tube
0.002 m^2
(default) | positive scalar
Internal flow area of each tube.
Dependencies
To enable this parameter, set Tube
cross-section to
Generic
.
Wetted perimeter of tube cross-section for pressure loss
— Perimeter of tube cross-section that fluid touches
0.15 m
(default) | positive scalar
Perimeter of the tube cross-section that the fluid touches. The
cross-section and perimeter are uniform along the tube. This value is
applied in pressure loss calculations.
Dependencies
To enable this parameter, set Tube
cross-section to
Generic
.
Perimeter of tube cross-section for heat transfer
— Perimeter of a single tube for heat transfer calculations
0.15 m
(default) | positive scalar
Tube perimeter for heat transfer calculations. This is often the same
as the tube perimeter, but in cases such as the annular cross-section,
this may be only the inner or outer diameter, depending on the
heat-transferring surface. The cross-section and tube perimeter are
uniform along the tube.
Dependencies
To enable this parameter, set Tube
cross-section to
Generic
.
Pressure loss model
— Method of pressure loss calculation due to viscous friction
Correlation for flow inside
tubes
(default) | Pressure loss coefficient
Method of pressure loss calculation due to viscous friction. The
settings are:
Pressure loss coefficient
. Use
this setting to calculate the pressure loss based on an
empirical loss coefficient.
Correlation for flow inside
tubes
. Use this setting to calculate the
pressure loss based on the pipe flow correlation.
Pressure loss coefficient, delta_p/(0.5*rho*v^2)
— Empirical loss coefficient for all pressure losses in channel
10
(default)
Empirical loss coefficient for all pressure losses in the channel.
This value accounts for wall friction and minor losses due to bends,
elbows, and other geometry changes in the channel.
The loss coefficient can be calculated from a nominal operating
condition or be tuned to fit experimental data. The loss coefficient is
defined as:
where Δp is the pressure drop,
ρ is the two-phase fluid density, and
v is the flow velocity.
Dependencies
To enable this parameter, set Pressure loss
model to Pressure loss
coefficient
.
Aggregate equivalent length of local resistances
— Combined length of all local resistances in the tubes
0.1 m
(default) | positive scalar
Combined length of all local resistances in the tubes. This parameter
describes the length of tubing that results in the same pressure losses
as the sum of all minor losses in the tube due to bends, tees, or
unions. A longer equivalent length results in larger pressure
losses.
Dependencies
To enable this parameter, set Pressure loss
model to Correlation for flow inside
tubes
.
Internal surface absolute roughness
— Mean surface roughness height
15e-6 m
(default) | positive scalar
Mean height of tube surface defects. A rougher wall results in larger
pressure losses in the turbulent regime for pressure loss calculated
with the Haaland correlation.
Dependencies
To enable this parameter, set either:
Pressure loss model
Heat transfer model
to Correlation for flow inside
tubes
.
Laminar flow upper Reynolds number limit
— Largest Reynolds number that indicates laminar flow
2000
(default) | positive scalar
Largest Reynolds number that indicates laminar flow. Between this
value and the Turbulent flow lower Reynolds number,
the flow regime is transitional.
Turbulent flow lower Reynolds number limit
— Smallest Reynolds number that indicates turbulent flow
4000
(default) | positive scalar
Smallest Reynolds number that indicates turbulent flow. Between this
value and the Laminar flow upper Reynolds number
limit, the flow regime is transitional.
Laminar friction constant for Darcy friction factor
— Coefficient of pressure loss due to viscous friction in laminar flows
64
(default) | positive scalar
Coefficient in pressure loss equations for viscous friction in laminar
flows. This parameter may also be known as the shape
factor. The default value corresponds to a circular tube
cross-section.
Dependencies
To enable this parameter, set Tube cross
section to Generic
and
Pressure loss model to
Correlation for flow inside
tubes
.
Heat transfer coefficient model
— Method of calculating heat transfer coefficient between fluid and wall
Correlation for flow inside
tubes
(default) | Colburn equation
Method of calculating the heat transfer coefficient between the fluid
and the wall. The available settings are:
Colburn equation
. Use this
setting to calculate the heat transfer coefficient with
user-defined variables a,
b, and c. In
the liquid and vapor zones, the heat transfer coefficient is
based on the Colburn equation. In the liquid-vapor mixture
zone, the heat transfer coefficient is based on the
Cavallini-Zecchin equation.
Correlation for flow inside
tubes
. Use this setting to calculate the
heat transfer coefficient for pipe flows. In the liquid and
vapor zones, the heat transfer coefficient is calculated
with the Gnielinski correlation. In the liquid-vapor mixture
zone, the heat transfer coefficient is calculated with the
Cavallini-Zecchin equation.
Coefficients [a, b, c] for a*Re^b*Pr^c in liquid zone
— Colburn equation coefficients in liquid zone
[.023, .8, .33]
(default) | three-element vector of positive scalars
Three-element vector containing the empirical coefficients of the
Colburn equation. Each fluid zone has a distinct Nusselt number, which
is calculated by the Colburn equation per zone. The general form of the
Colburn equation is:
Dependencies
To enable this parameter, set Heat transfer coefficient
model to Colburn
equation
.
Coefficients [a, b, c] for a*Re^b*Pr^c in mixture zone
— Cavallini-Zecchin equation coefficients in mixture zone
[.05, .8, .33]
(default) | three-element vector of positive scalars
Three-element vector containing the empirical coefficients of the
Cavallini-Zecchin equation. Each fluid zone has a distinct Nusselt
number, which is calculated in the mixture zone by the Cavallini-Zecchin equation:
Dependencies
To enable this parameter, set Heat transfer coefficient
model to Colburn
equation
.
Coefficients [a, b, c] for a*Re^b*Pr^c in vapor zone
— Colburn equation coefficients in vapor zone
[.023, .8, .33]
(default) | three-element vector of positive scalars
Three-element vector containing the empirical coefficients of the
Colburn equation. Each fluid zone has a distinct Nusselt number, which
is calculated by the Colburn equation per zone. The general form of the
Colburn equation is:
Dependencies
To enable this parameter, set Heat transfer coefficient
model to Colburn
equation
.
Laminar flow Nusselt number
— Ratio of convective to conductive heat transfer in the laminar flow regime
3.66
(default) | positive scalar
Ratio of convective to conductive heat transfer in the laminar flow
regime. The fluid Nusselt number influences the heat transfer rate and
depends on the tube cross-section.
Dependencies
To enable this parameter, set Heat transfer coefficient
model to Correlation for flow inside
tubes
.
Fouling factor
— Additional thermal resistance due to fouling deposits
0.1 m^2*K/kW
(default) | positive scalar
Additional thermal resistance due to fouling layers on the surfaces of
the wall. In real systems, fouling deposits grow over time. However, the
growth is slow enough to be assumed constant during the
simulation.
Total fin surface area
— Total heat transfer surface area of fins
0 m^2
(default) | positive scalar
Total heat transfer surface area of both sides of all fins. For
example, if the fin is rectangular, the surface area is double the area
of the rectangle.
The total heat transfer surface area is the sum of the channel surface
area and the effective fin surface area, which is the product of the
Fin efficiency and the Total fin
surface area.
Fin efficiency
— Ratio of fin actual to ideal heat transfer rates
0.5
(default) | positive scalar in the range [0,1]
Ratio of actual heat transfer to ideal heat transfer through the
fins.
Initial fluid energy specification
— Initial state of the two-phase fluid
Temperature
(default) | Vapor quality
| Vapor void fraction
| Specific enthalpy
| Specific internal energy
Quantity used to describe the initial state of the fluid: temperature,
vapor quality, vapor void fraction, specific enthalpy, or specific
internal energy.
Initial two-phase fluid pressure
— Fluid pressure at start of simulation
0.101325 MPa
(default) | positive scalar
Fluid pressure at the start of the simulation.
Initial two-phase fluid temperature
— Temperature at start of simulation
293.15 K
(default) | positive scalar | two-element vector
Temperature in the two-phase fluid channel at the start of simulation.
This parameter can be a scalar or a two-element vector. A scalar value
represents the mean initial temperature in the channel. A vector value
represents the initial temperature at the inlet and outlet in the form
[inlet
, outlet
]. The block
calculates a linear gradient between the two ports. The inlet and the
outlet ports are identified according to the initial flow
direction.
Dependencies
To enable this parameter, set Initial fluid energy
specification to
Temperature
.
Initial two-phase fluid vapor quality
— Vapor mass fraction at start of simulation
0.5
(default) | positive scalar in the range [0,1] | two-element vector
Vapor mass fraction in the two-phase fluid channel at the start of
simulation. This parameter can be a scalar or a two-element vector. A
scalar value represents the mean initial vapor quality in the channel. A
vector value represents the initial vapor quality at the inlet and
outlet in the form [inlet
,
outlet
]]. The block calculates a linear gradient
between the two ports. The inlet and the outlet ports are identified
according to the initial flow direction.
Dependencies
To enable this parameter, set Initial fluid energy
specification to Vapor
quality
.
Initial two-phase fluid vapor void fraction
— Vapor volume fraction at start of simulation
0.5
(default) | positive scalar in the range [0,1] | two-element vector
Vapor volume fraction in the two-phase fluid channel at the start of
simulation. This parameter can be a scalar or a two-element vector. A
scalar value represents the mean initial void fraction in the channel. A
vector value represents the initial void fraction at the inlet and
outlet in the form [inlet
,
outlet
]. The block calculates a linear gradient
between the two ports. The inlet and the outlet ports are identified
according to the initial flow direction.
Dependencies
To enable this parameter, set Initial fluid energy
specification to Vapor void
fraction
.
Initial two-phase fluid specific enthalpy
— Enthalpy per unit mass at start of simulation
1500 kJ/kg
(default) | positive scalar | two-element vector
Enthalpy per unit mass in the two-phase fluid channel at the start of
simulation. This parameter can be a scalar or a two-element vector. A
scalar value represents the mean initial specific enthalpy in the
channel. A vector value represents the initial specific enthalpy at the
inlet and outlet in the form [inlet
,
outlet
]. The block calculates a linear gradient
between the two ports. The inlet and the outlet ports are identified
according to the initial flow direction.
Dependencies
To enable this parameter, set Initial fluid energy
specification to Specific
enthalpy
.
Initial two-phase fluid specific internal energy
— Internal energy per unit mass at start of simulation
1500 kJ/kg
(default) | positive scalar | two-element vector
Internal energy per unit mass in the two-phase fluid channel at the
start of simulation. This parameter can be a scalar or a two-element
vector. A scalar value represents the mean initial specific internal
energy in the channel. A vector value represents the initial specific
internal energy at the inlet and outlet in the form
[inlet
, outlet
]. The block
calculates a linear gradient between the two ports. The inlet and the
outlet ports are identified according to the initial flow
direction.
Dependencies
To enable this parameter, set Initial fluid energy
specification to Specific internal
energy
.
Moist Air 2
Flow geometry
— Moist air flow configuration
Flow perpendicular to bank of circular
tubes
(default) | Flow inside one or more tubes
| Generic
Moist air flow path. The flow can run externally over a set of tubes
or internal to a tube or set of tubes. You can also specify a generic
parameterization based on empirical values.
Number of tubes
— Number of moist air tubes
25
(default) | positive scalar
Number of moist air tubes. More tubes result in higher pressure losses
due to viscous friction, but a larger amount of surface area for heat
transfer.
Dependencies
To enable this parameter, set Flow geometry
to Flow inside one or more tubes
.
Total length of each tube
— Total length of each moist air tube
1 m
(default) | positive scalar
Total length of each moist air tube.
Dependencies
To enable this parameter, set Flow geometry
to Flow inside one or more tubes
.
Tube cross section
— Cross-sectional shape of a tube
Circular
(default) | Rectangular
| Annular
| Generic
Cross-sectional shape of one tube. Set to
Generic
to specify an arbitrary
cross-sectional geometry.
Dependencies
To enable this parameter, set Flow geometry
to Flow inside one or more tubes
.
Tube inner diameter
— Internal diameter of a single tube
0.05 m
(default) | positive scalar
Internal diameter of the cross-section of one tube. The cross-section
and diameter are uniform along the tube. The size of the diameter
influences the pressure loss and heat transfer calculations.
Dependencies
To enable this parameter, set Flow geometry
to Flow inside one or more tubes
and
Tube cross-section to
Circular
.
Tube width
— Internal width of a single tube
0.05 m
(default) | positive scalar
Internal width of the cross-section of one tube. The cross-section and
width are uniform along the tube. The width and height influence the
pressure loss and heat transfer calculations.
Dependencies
To enable this parameter, set Flow geometry
to Flow inside one or more tubes
and
Tube cross-section to
Rectangular
.
Tube height
— Internal height of a single tube
0.05 m
(default) | positive scalar
Internal height of one tube cross-section. The cross-section and
height are uniform along the tube. The width and height influence the
pressure loss and heat transfer calculations.
Dependencies
To enable this parameter, set Flow geometry
parameterization of Flow inside one or more
tubes
and Tube cross-section
to Rectangular
.
Annulus inner diameter (heat transfer surface)
— Smaller diameter of annular cross-section
0.05 m
(default) | positive scalar
Smaller diameter of the annular cross-section of one tube. The
cross-section and inner diameter are uniform along the tube. The inner
diameter influences the pressure loss and heat transfer calculations.
Heat transfer occurs through the inner surface of the annulus.
Dependencies
To enable this parameter, set Flow geometry
parameterization of Flow inside one or more
tubes
and Tube cross-section
to Annular
.
Annulus outer diameter
— Larger diameter of annular cross-section
0.1 m
(default) | positive scalar
Larger diameter of the annular cross-section of one tube. The
cross-section and outer diameter are uniform along the tube. The outer
diameter influences the pressure loss and heat transfer
calculations.
Dependencies
To enable this parameter, set Flow geometry
to Flow inside one or more tubes
and
Tube cross-section to
Annular
.
Cross-sectional area per tube
— Internal flow area in each tube
0.002 m^2
(default) | positive scalar
Internal flow area of each tube.
Dependencies
To enable this parameter, set Flow geometry
to Flow inside one or more tubes
and
Tube cross-section to
Generic
.
Wetted perimeter of tube cross-section for pressure loss
— Perimeter of tube cross-section that fluid touches
0.15 m
(default) | positive scalar
Perimeter of the tube cross-section that the fluid touches. The
cross-section and perimeter are uniform along the tube. This value is
applied in pressure loss calculations.
Dependencies
To enable this parameter, set Flow geometry
to Flow inside one or more tubes
and
Tube cross-section to
Generic
.
Perimeter of tube cross-section for heat transfer
— Perimeter of a single tube for heat transfer calculations
0.15 m
(default) | positive scalar
Tube perimeter for heat transfer calculations. This is often the same
as the tube perimeter, but in cases such as the annular cross-section,
this may be only the inner or outer diameter, depending on the
heat-transferring surface. The cross-section and tube perimeter are
uniform along the tube.
Dependencies
To enable this parameter, set Flow geometry
to Flow inside one or more tubes
and
Tube cross-section to
Generic
.
Pressure loss model
— Method of pressure loss calculation due to viscous friction
Correlation for flow inside
tubes
(default) | Euler number per tube row
| Pressure loss coefficient
| Correlation for flow over tube
bank
Method of pressure loss calculation due to viscous friction. Different
models are available for different flow configurations. The settings are:
Correlation for flow inside
tubes
. Use this setting to calculate the
pressure loss with the Haaland correlation.
Pressure loss coefficient
. Use
this setting to calculate the pressure loss based on an
empirical loss coefficient.
Euler number per tube row
. Use
this setting to calculate the pressure loss based on an
empirical Euler number.
Correlation for flow over tube
bank
. Use this setting to calculate the
pressure loss based on the Hagen number.
The pressure loss models available depend on the Flow
geometry setting.
Dependencies
When Flow geometry is set to
Flow inside one or more tubes
,
Pressure loss model can be set to either:
When Flow geometry is set to
Flow perpendicular to bank of circular
tubes
, Pressure loss model
can be set to either:
When Flow geometry is set to
Generic
, the Pressure loss
model parameter is disabled. Pressure loss is
calculated empirically with the Pressure loss coefficient,
delta_p/(0.5*rho*v^2) parameter.
Pressure loss coefficient, delta_p/(0.5*rho*v^2)
— Empirical loss coefficient for all pressure losses in the channel
10
(default) | positive scalar
Empirical loss coefficient for all pressure losses in the channel.
This value accounts for wall friction and minor losses due to bends,
elbows, and other geometry changes in the channel.
The loss coefficient can be calculated from a nominal operating
condition or be tuned to fit experimental data. The pressure loss
coefficient is defined as:
where Δp is the pressure drop,
ρ is the two-phase fluid density, and
v is the flow velocity.
Dependencies
To enable this parameter, set either:
Aggregate equivalent length of local resistances
— Combined length of all local resistances in the tubes
0.1 m
(default) | positive scalar
Combined length of all local resistances in the tubes. This is the
length of tubing that results in the same pressure losses as the sum of
all minor losses in the tube due to such things as bends, tees, or
unions. A longer equivalent length results in larger pressure
losses.
Dependencies
To enable this parameter, set Pressure loss
model to Correlations for flow inside
tubes
.
Internal surface absolute roughness
— Mean surface roughness height
15e-6 m
(default) | positive scalar
Mean height of tube surface defects. A rougher wall results in larger
pressure losses in the turbulent regime for pressure loss calculated
with the Haaland correlation.
Dependencies
To enable this parameter, set either:
to Correlation for flow inside
tubes
.
Laminar flow upper Reynolds number limit
— Largest Reynolds number that indicates laminar flow
2000
(default) | positive scalar
Largest Reynolds number that indicates laminar flow. Between this
value and the Turbulent flow lower Reynolds number
limit, the flow regime is transitional.
Dependencies
To enable this parameter, set Flow geometry
to Flow inside one or more tubes
and
Pressure loss model to
Correlation for flow inside
tubes
.
Turbulent flow lower Reynolds number limit
— Smallest Reynolds number that indicates turbulent flow
4000
(default) | positive scalar
Smallest Reynolds number that indicates turbulent flow. Between this
value and the Laminar flow upper Reynolds number
limit, the flow regime is transitional between the
laminar and turbulent regimes.
Dependencies
To enable this parameter, set Flow geometry
to Flow inside one or more tubes
and
Pressure loss model to
Correlation for flow inside
tubes
.
Laminar friction constant for Darcy friction factor
— Coefficient of pressure loss due to viscous friction in laminar flows
64
(default) | positive scalar
Coefficient in pressure loss equations for viscous friction in laminar
flows. This parameter is also known as the shape
factor. The default value corresponds to a circular tube
cross-section.
Dependencies
To enable this parameter, set Flow geometry
to Correlation for flow inside tubes
,
Tube cross section to
Generic
, and Pressure loss
model to Correlation for flow inside
tubes
.
Heat transfer coefficient model
— Method of calculating heat transfer coefficient between fluid and wall
Correlation for flow over tube
bank
(default) | Colburn equation
| Correlation for flow inside tubes
Method of calculating the heat transfer coefficient between the fluid
and the wall. The available settings are:
Colburn equation
. Use this
setting to calculate the heat transfer coefficient with
user-defined variables a,
b, and c of
the Colburn equation.
Correlation for flow over tube
bank
. Use this setting to calculate the
heat transfer coefficient based on the tube bank correlation
using the Hagen number.
Correlation for flow inside
tubes
. Use this setting to calculate the
heat transfer coefficient for pipe flows with the Gnielinski
correlation.
Dependencies
To enable this parameter, set Flow geometry
to either:
Coefficients [a, b, c] for a*Re^b*Pr^c
— Colburn equation coefficients
[0.023, 0.8, 0.33]
(default) | three-element vector
Three-element vector containing the empirical coefficients of the
Colburn equation. The Colburn equation is a formulation for calculating
the Nusselt Number. The general form of the Colburn equation is:
When the Heat transfer coefficient model is set
to Colburn equation and Flow
geometry is set to Flow inside one or more
tubes
, or Flow geometry is set to
Generic
, the default Colburn equation is:
When the Heat transfer coefficient
model is set to Colburn equation and
Flow geometry is set to Flow
perpendicular to bank of circular tubes
, the default
Colburn equation is:
Dependencies
To enable this parameter, set:
Flow geometry to either:
and Heat transfer coefficient
model to Colburn
equation
.
Flow geometry to
Generic
.
Laminar flow Nusselt number
— Ratio of convective to conductive heat transfer in laminar flow regime
3.66
(default) | positive scalar
Ratio of convective to conductive heat transfer in the laminar flow
regime. The fluid Nusselt number influences the heat transfer rate and
depends on the tube cross-section.
Dependencies
To enable this parameter, set Flow geometry
to Flow inside one or more tubes
,
Tube cross-section to
Generic
, and Heat transfer
parameterization to Correlation for flow
inside tubes
.
Tube bank grid arrangement
— Geometrical placement of tube rows in the bank
Inline
(default) | Staggered
Alignment of tubes in a tube bank. Rows are either in line with their
neighbors, or staggered.
Tube alignment influences the Nusselt number and the heat transfer
rate.
Dependencies
To enable this parameter, set Flow geometry
to Flow perpendicular to bank of circular
tubes
.
Number of tube rows along flow direction
— Number of tube rows in tube bank
5
(default) | positive scalar
Number of two-phase fluid tube rows in a tube bank. The rows are
aligned with the direction of moist air flow.
Dependencies
To enable this parameter, set Flow geometry
to Flow perpendicular to bank of circular
tubes
.
Number of tube segments in each tube row
— Number of two-phase fluid tubes in each row of the tube bank
5
(default) | positive scalar
Number of two-phase fluid tubes in each row of a tube bank. This
measurement is perpendicular to the moist air flow.
Dependencies
To enable this parameter, set Flow geometry
to Flow perpendicular to bank of circular
tubes
.
Length of each tube segment in a tube row
— Length of each two-phase fluid tube
1 m
(default) | positive scalar
Length of each two-phase fluid tube that spans a tube row. All tubes
in a tube bank are the same length.
Dependencies
To enable this parameter, set Flow geometry
to Flow perpendicular to bank of circular
tubes
.
Tube outer diameter
— Outer diameter of a single two-phase fluid tube
0.05 m
(default) | positive scalar
Outer diameter of a two-phase fluid tube. The cross-section is uniform
along a tube and so the diameter is constant throughout. This value
influences the losses in the flow across a tube bank due to viscous
friction.
Dependencies
To enable this parameter, set Flow geometry
to Flow perpendicular to bank of circular
tubes
.
Longitudinal tube pitch (along flow direction)
— Center-to-center distance between two-phase fluid tube rows
0.15 m
(default) | positive scalar
Distance between tube centers of the two-phase fluid tubes, aligned
with the direction of flow of the moist air.
Dependencies
To enable this parameter, set Flow geometry
to Flow perpendicular to bank of circular
tubes
.
Transverse tube pitch (perpendicular to flow direction)
— Center-to-center distance between two-phase fluid tubes in a row
0.15 m
(default) | positive scalar
Distance between the tube centers in a row of two-phase fluid tubes.
This measurement is perpendicular to the moist air flow direction. See
Heat Transfer Coefficient for Flows Across a Tube Bank for
more information.
Dependencies
To enable this parameter, set Flow geometry
to Flow perpendicular to bank of circular
tubes
.
Euler number per tube row, delta_p/(N*0.5*rho*v^2)
— Euler number for each row of the tube bank
10
(default) | positive scalar
Empirical coefficient for pressure drop across one tube row. The Euler
number is the ratio between pressure drop and fluid momentum:
where N is the Number of
tube rows along flow direction, Δp is
the pressure drop, ρ is the moist air mixture
density, and v is the flow velocity.
Each tube row is located in a plane perpendicular to the moist air
flow.
Dependencies
To enable this parameter, set Flow geometry
to Flow perpendicular to bank of circular
tubes
and Pressure loss model
to Euler number per tube row
.
Minimum free-flow area
— Smallest total flow area between inlet and outlet
0.01 m^2
(default) | positive scalar
Smallest total flow area between inlet and outlet. If the channel is a
collection of ducts, tubes, slots, or grooves, the minimum free-flow
area is the sum of the smallest areas.
Dependencies
To enable this parameter, set Flow geometry
to Generic
.
Heat transfer surface area without fins
— Total area of the heat transfer surface excluding fins
2 m^2
(default) | positive scalar
Total area of the heat transfer surface, excluding fins.
Dependencies
To enable this parameter, set Flow geometry
to Generic
.
Moist air volume inside heat exchanger
— Total volume of moist air in the heat exchanger
0.05 m^3
(default) | positive scalar
Total volume of moist air in the heat exchanger.
Dependencies
To enable this parameter, set Flow geometry
to Generic
.
Fouling factor
— Additional thermal resistance due to fouling deposits
0.1 m^2*K/kW
(default) | positive scalar
Additional thermal resistance due to fouling layers on the surfaces of
the wall. In real systems, fouling deposits grow over time. However, the
growth is slow enough to be assumed constant during the
simulation.
Total fin surface area
— Total heat transfer surface area of all fins
0 m^2
(default) | positive scalar
Total heat transfer surface area of both sides of all fins. For
example, if the fin is rectangular, the surface area is double the area
of the rectangle.
The total heat transfer surface area is the sum of the channel surface
area and the effective fin surface area, which is the product of the
Fin efficiency and the Total fin
surface area.
Fin efficiency
— Ratio of fin actual to idea heat transfer rates
0.5
(default) | positive scalar in the range [0,1]
Ratio of actual heat transfer to ideal heat transfer through the
fins.
Initial moist air pressure
— Moist air pressure at start of simulation
0.101325 MPa
(default) | positive scalar
Moist air pressure at the start of the simulation.
Initial moist air temperature
— Temperature at the start of simulation
293.15 K
(default) | positive scalar | two-element vector
Temperature in the moist air fluid channel at the start of the
simulation. This parameter can be a scalar or a two-element vector. A
scalar value represents the mean initial temperature in the channel. A
vector value represents the initial temperature at the inlet and outlet
in the form [inlet
, outlet
]. The
block calculates a linear gradient between the two ports. The inlet and
the outlet ports are identified according to the initial flow
direction.
Initial moisture specification
— Moisture specification
Relative humidity
(default) | Specific humidity
| Mole fraction
| Humidity ratio
Moisture specification, which can be set as relative humidity,
specific humidity, water vapor mole fraction, or humidity ratio.
Initial moist air relative humidity
— Relative humidity at the start of simulation
0.5
(default) | positive scalar in the range of [0,1] | two-element vector
Relative humidity in the moist air channel at the start of the
simulation. The relative humidity is the ratio of the water vapor
partial pressure to the water vapor saturation pressure, or the ratio of
the water vapor mole fraction to the water vapor mole fraction at
saturation.
This parameter can be a scalar or a two-element vector. A scalar value
represents the mean initial relative humidity in the channel. A vector
value represents the initial relative humidity at the inlet and outlet
in the form [inlet
, outlet
]. The
block calculates a linear gradient between the two ports. The inlet and
the outlet ports are identified according to the initial flow
direction.
Dependencies
To enable this parameter, set Initial moisture
specification to Relative
humidity
.
Initial moist air specific humidity
— Specific humidity at the start of simulation
0.01
(default) | positive scalar in the range of [0,1] | two-element vector
Specific humidity in the moist air channel at the start of simulation.
The specific humidity is the mass fraction of water vapor to the
combined total mass of water vapor, trace gas, and dry air.
This parameter can be a scalar or a two-element vector. A scalar value
represents the mean initial specific humidity in the channel. A vector
value represents the initial specific humidity at the inlet and outlet
in the form [inlet
, outlet
]. The
block calculates a linear gradient between the two ports. The inlet and
the outlet ports are identified according to the initial flow
direction.
Dependencies
To enable this parameter, set Initial moisture
specification to Specific
humidity
.
Initial moist air water vapor mole fraction
— Mole fraction of water vapor at the start of simulation
0.01
(default) | positive scalar in the range [0,1] | two-element vector
Mole fraction of the water vapor in the moist air channel at the start
of simulation. The water vapor mole fraction is relative to the combined
molar quantity of water vapor, trace species, and dry air.
This parameter can be a scalar or a two-element vector. A scalar value
represents the mean initial vapor mole fraction in the channel. A vector
value represents the initial vapor mole fraction at the inlet and outlet
in the form [inlet
, outlet
]. The
block calculates a linear gradient between the two ports. The inlet and
the outlet ports are identified according to the initial flow
direction.
Dependencies
To enable this parameter, set Initial moisture
specification to Mole
fraction
.
Initial moist air humidity ratio
— Humidity ratio at the start of simulation
0.01
(default) | positive scalar in the range [0,1] | two-element vector
Humidity ratio in the moist air channel at the start of the
simulation. The humidity ratio is the ratio of the mass of water vapor
to the mass of dry air and trace gas.
This parameter can be a scalar or a two-element vector. A scalar value
represents the mean initial humidity ratio in the channel. A vector
value represents the initial humidity ratio at the inlet and outlet in
the form [inlet
, outlet
]. The
block calculates a linear gradient between the two ports. The inlet and
the outlet ports are identified according to the initial flow
direction.
Dependencies
To enable this parameter, set Initial moisture
specification to Humidity
ratio
.
Initial trace gas specification
— Measurement type of trace gas
Mass fraction
(default) | Mole fraction
Measurement type of trace gas.
Initial moist air trace gas mass fraction
— Amount of trace gas in the moist air channel
0.001
(default) | positive scalar in the range of [0,1] | two-element vector
Amount of trace gas in the moist air channel by mass fraction at the
start of the simulation. The mass fraction is relative to the combined
total mass of water vapor, trace gas, and dry air.
This parameter can be a scalar or a two-element vector. A scalar value
represents the mean trace gas mass fraction in the channel. A vector
value represents the initial trace gas mass fraction at the inlet and
outlet in the form [inlet
,
outlet
]. The block calculates a linear gradient
between the two ports. The inlet and the outlet ports are identified
according to the initial flow direction.
This parameter is ignored if the Trace gas model
parameter in the Moist Air Properties (MA) block is set to
None
.
Dependencies
To enable this parameter, set Initial trace gas
specification to Mass
fraction
.
Initial moist air trace gas mole fraction
— Mole fraction of trace gas at the start of simulation
0.001
(default) | positive scalar in the range of [0,1] | two-element vector
Amount of trace gas in the moist air channel by mole fraction at the
start of the simulation. The mole fraction is relative to the combined
molar total of water vapor, trace gas, and dry air.
This parameter can be a scalar or a two-element vector. A scalar value
represents the mean trace gas mole fraction in the channel. A vector
value represents the initial trace gas mole fraction at the inlet and
outlet in the form [inlet
,
outlet
]. The block calculates a linear gradient
between the two ports. The inlet and the outlet ports are identified
according to the initial flow direction.
This parameter is ignored if the Trace gas model
parameter in the Moist Air Properties (MA) block is set to
None
.
Dependencies
To enable this parameter, set Initial trace gas
specification to Mole
fraction
.
Relative humidity at saturation
— Relative humidity point of condensation
1
(default) | positive scalar in the range of [0,1]
Relative humidity point of condensation. Condensation occurs above
this value. A value greater than 1 indicates a supersaturated
vapor.
References
[1] 2013
ASHRAE Handbook - Fundamentals. American Society of Heating,
Refrigerating and Air-Conditioning Engineers, Inc., 2013.
[2] Braun, J. E., S. A. Klein, and
J. W. Mitchell. "Effectiveness Models for Cooling Towers and Cooling Coils."
ASHRAE Transactions 95, no. 2, (June 1989):
164–174.
[3] Çengel, Yunus A. Heat and Mass Transfer: A Practical Approach. 3rd ed,
McGraw-Hill, 2007.
[4] Ding, X., Eppe J.P., Lebrun,
J., Wasacz, M. "Cooling Coil Model to be Used in Transient and/or Wet Regimes.
Theoretical Analysis and Experimental Validation." Proceedings of the Third
International Conference on System Simulation in Buildings (1990):
405-411.
[5] Mitchell, John W., and James
E. Braun. Principles of Heating, Ventilation, and Air
Conditioning in Buildings. Wiley, 2013.
[6] Shah, R. K., and Dušan P. Sekulić. Fundamentals of Heat Exchanger Design. John Wiley & Sons,
2003.
[7] White, Frank M. Fluid Mechanics. 6th ed, McGraw-Hill, 2009.
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