# System-Level Heat Exchanger (TL-MA)

Heat exchanger between thermal liquid and moist air networks, with model based on performance data

• Library:
• Simscape / Fluids / Fluid Network Interfaces / Heat Exchangers

## Description

The System-Level Heat Exchanger (TL-MA) block models a heat exchanger between a thermal liquid network and a moist air network.

The block model is based on performance data from the heat exchanger datasheet, rather than on the detailed geometry of the exchanger, and therefore lets you easily adjust the size and performance of the heat exchanger during design iterations, or model heat exchangers with uncommon geometries. You can also use this block to model heat exchangers with a certain level of performance at an early design stage, when detailed geometry data is not yet available.

You parameterize the block by the nominal operating condition. The heat exchanger is sized to match the specified performance at the nominal operating condition at steady state.

The Moist Air 2 side models water vapor condensation based on convective water vapor mass transfer with the heat transfer surface. Condensed water is removed from the moist air flow.

This block is similar to the Heat Exchanger (TL-MA) block but uses a different parameterization model. The table provides a comparison of the two blocks, to help you choose the right block for your application.

Heat Exchanger (TL-MA)System-Level Heat Exchanger (TL-MA)
Block parameters are based on the heat exchanger geometryBlock parameters are based on performance and operating conditions
Heat exchanger geometry may be limited by the available geometry parameter optionsModel is independent of the specific heat exchanger geometry
You can adjust the block for different performance requirements by tuning geometry parameters, such as fin sizes and tube lengthsYou can adjust the block for different performance requirements by directly specifying the desired heat and mass flow rates
Lets you select between parallel, counter, or cross flow configurationsLets you select between parallel, counter, or cross flow arrangement at nominal operating conditions, to help with sizing
Predictively accurate results over a wide range of operating conditions, subject to the applicability of the E-NTU equations and the heat transfer coefficient correlationsVery accurate results around the specified operating condition; accuracy may decrease far away from the specified operating conditions
Heat transfer calculations account for the variation of temperature along the flow path by using the E-NTU modelHeat transfer calculations approximate the variation of temperature along the flow path by dividing it into three segments
Accounts for water vapor condensation and the latent heat on the moist air flowAccounts for water vapor condensation and the latent heat on the moist air flow
Does not model the wall thermal mass; you can approximate the effect by connecting a pipe block with a thermal mass downstreamIncludes an option to model the wall thermal mass

### Heat Transfer

The thermal liquid flow and the moist air flow are each divided into three segments of equal size. Heat transfer between the fluids is calculated in each segment. For simplicity, the equation for one segment is shown here.

If the wall thermal mass is off, then the heat balance in the heat exchanger is

`${Q}_{seg,TL}+{Q}_{seg,MA}=0,$`

where:

• Qseg,TL is the heat flow rate from the wall (that is, the heat transfer surface) to the thermal liquid in the segment.

• Qseg,MA is the heat flow rate from the wall to the moist air in the segment.

If the wall thermal mass is on, then the heat balance in the heat exchanger is

`${Q}_{seg,TL}+{Q}_{seg,MA}=-\frac{{M}_{wall}{c}_{{p}_{wall}}}{N}\frac{d{T}_{seg,wall}}{dt},$`

where:

• Mwall is the mass of the wall.

• cpwall is the specific heat of the wall.

• N = 3 is the number of segments.

• Tseg,wall is the average wall temperature in the segment.

• t is time.

The heat flow rate from the wall to the thermal liquid in the segment is

`${Q}_{seg,TL}=U{A}_{seg,TL}\left({T}_{seg,wall}-{T}_{seg,TL}\right),$`

where:

• UAseg,TL is the heat transfer conductance for the thermal liquid in the segment.

• Tseg,TL is the average liquid temperature in the segment.

The heat flow rate from the wall to the moist air in the segment is

`${Q}_{seg,MA}=\frac{U{A}_{seg,MA}}{{\overline{c}}_{{p}_{seg,MA}}}\left({\overline{h}}_{seg,wall}-{\overline{h}}_{seg,MA}\right)+{\stackrel{˙}{m}}_{w,seg,cond}{h}_{l,wall},$`

where:

• UAseg,MA is the heat transfer conductance for the moist air in the segment.

• ${\overline{c}}_{{p}_{seg,MA}}$ is the moist air mixture specific heat per unit mass of dry air and trace gas in the segment.

• ${\overline{h}}_{seg,wall}$ is the moist air mixture enthalpy per unit mass of dry air and trace gas at the average wall segment temperature.

• ${\overline{h}}_{seg,MA}$ is the moist air mixture enthalpy per unit mass of dry air and trace gas in the segment.

• ${\stackrel{˙}{m}}_{w,seg,cond}$ is the rate of water vapor condensation on the wall surface.

• hl,wall is the specific enthalpy of liquid water at the average wall segment temperature.

Using mixture enthalpy in this equation accounts for both differences in temperature and differences in moisture due to condensation [3].

Note

For the moist air quantities, the bar above the symbols indicates that they are quantities for mixture divided by the mass of dry air and trace gas only, as opposed to dividing by the mass of the whole mixture. The whole mixture includes dry air, water vapor, and trace gas.

### Thermal Liquid Heat Transfer Correlation

The heat transfer conductance is

`$U{A}_{seg,TL}={a}_{TL}{\left({\mathrm{Re}}_{seg,TL}\right)}^{{b}_{TL}}{\left({\mathrm{Pr}}_{seg,TL}\right)}^{{c}_{TL}}{k}_{seg,TL}\frac{{G}_{TL}}{N},$`

where:

• aTL, bTL, and cTL are the coefficients of the Nusselt number correlation. These coefficients appear as block parameters in the Correlation Coefficients section.

• Reseg,TL is the average Reynolds number for the segment.

• Prseg,TL is the average Prandtl number for the segment.

• kseg,TL is the average thermal conductivity for the segment.

• GTL is the geometry scale factor for the thermal liquid side of the heat exchanger. The block calculates the geometry scale factor so that the total heat transfer over all segments matches the specified performance at the nominal operating conditions.

The average Reynolds number is

`${\mathrm{Re}}_{seg,\text{TL}}=\frac{{\stackrel{˙}{m}}_{seg,\text{TL}}{D}_{ref,\text{TL}}}{{\mu }_{seg,\text{TL}}{S}_{ref,\text{TL}}},$`

where:

• ${\stackrel{˙}{m}}_{seg,\text{TL}}$ is the mass flow rate through the segment.

• μseg,TL is the average dynamic viscosity for the segment.

• Dref,TL is an arbitrary reference diameter.

• Sref,TL is an arbitrary reference flow area.

Note

The Dref,TL and Sref,TL terms are included in this equation for unit calculation purposes only, to make Reseg,TL nondimensional. The values of Dref,TL and Sref,TL are arbitrary because the GTL calculation overrides these values.

### Moist Air Heat Transfer Correlation

The heat transfer conductance is

`$U{A}_{seg,MA}={a}_{MA}{\left({\mathrm{Re}}_{seg,MA}\right)}^{{b}_{MA}}{\left({\mathrm{Pr}}_{seg,MA}\right)}^{{c}_{MA}}{k}_{seg,MA}\frac{{G}_{MA}}{N},$`

where:

• aMA, bMA, and cMA are the coefficients of the Nusselt number correlation. These coefficients appear as block parameters in the Correlation Coefficients section.

• Reseg,MA is the average Reynolds number for the segment.

• Prseg,MA is the average Prandtl number for the segment.

• kseg,MA is the average thermal conductivity for the segment.

• GMA is the geometry scale factor for the moist air side of the heat exchanger. The block calculates the geometry scale factor so that the total heat transfer over all segments matches the specified performance at the nominal operating conditions.

The average Reynolds number is

`${\mathrm{Re}}_{seg,MA}=\frac{{\stackrel{˙}{m}}_{seg,MA}{D}_{ref,MA}}{{\mu }_{seg,MA}{S}_{ref,MA}},$`

where:

• ${\stackrel{˙}{m}}_{seg,MA}$ is the mass flow rate through the segment.

• μseg,MA is the average dynamic viscosity for the segment.

• Dref,MA is an arbitrary reference diameter.

• Sref,MA is an arbitrary reference flow area.

Note

The Dref,MA and Sref,MA terms are included in this equation for unit calculation purposes only, to make Reseg,MA nondimensional. The values of Dref,MA and Sref,MA are arbitrary because the GMA calculation overrides these values.

### Moist Air Condensation

The equation describing the heat flow rate from the wall to the moist air in the segment (the last equation in the Heat Transfer section) uses the average moist air mixture enthalpy, ${\overline{h}}_{seg,MA}$, and the wall segment moist air mixture enthalpy, ${\overline{h}}_{seg,wall}$.

The average moist air mixture enthalpy is based on the temperature and humidity of the moist air flow through the segment:

`${\overline{h}}_{seg,MA}={h}_{seg,ag,MA}+{W}_{seg,MA}{h}_{seg,w,MA},$`

where:

• hseg,ag,MA is the average specific enthalpy of dry air and trace gas for the segment.

• hseg,w,MA is the average specific enthalpy of water vapor for the segment.

• Wseg,MA is the humidity ratio of the segment.

The wall segment moist air mixture enthalpy is based on the temperature and humidity at the wall segment:

`${\overline{h}}_{seg,wall}={h}_{seg,ag,wall}+{W}_{seg,wall}{h}_{seg,w,wall},$`

where:

• hseg,ag,wall is the specific enthalpy of dry air and trace gas at the wall segment temperature.

• hseg,w,wall is the specific enthalpy of water vapor at the wall segment temperature.

• Wseg,wall is the humidity ratio at the wall segment:

`${W}_{seg,wall}=\mathrm{min}\left({W}_{seg,MA},{W}_{seg,s,wall}\right),$`

where Wseg,s,wall is the saturated humidity ratio at the wall segment temperature. In other words, the humidity ratio at the wall is the same as the humidity ratio of the moist air flow but not more than the maximum that can be supported at the wall segment temperature.

When Wseg,s,wall < Wseg,MA, water vapor condensation occurs on the wall surface. The rate of water vapor condensation is

`${\stackrel{˙}{m}}_{w,seg,cond}=\frac{U{A}_{seg,MA}}{{\overline{c}}_{{p}_{seg,MA}}}\left({W}_{seg,MA}-{W}_{seg,wall}\right).$`

The condensed water is assumed to be drained from the wall surface and is thus removed from the moist air flow downstream.

### Pressure Loss

The pressure losses on the thermal liquid side are

`$\begin{array}{l}{p}_{A,\text{TL}}-{p}_{\text{TL}}=\frac{{K}_{\text{TL}}}{2}\frac{{\stackrel{˙}{m}}_{A,\text{TL}}\sqrt{{\stackrel{˙}{m}}^{2}{}_{A,\text{TL}}+{\stackrel{˙}{m}}^{2}{}_{thres,\text{TL}}}}{2{\rho }_{avg,2P}}\\ {p}_{B,\text{TL}}-{p}_{\text{TL}}=\frac{{K}_{\text{TL}}}{2}\frac{{\stackrel{˙}{m}}_{B,\text{TL}}\sqrt{{\stackrel{˙}{m}}^{2}{}_{B,\text{TL}}+{\stackrel{˙}{m}}^{2}{}_{thres,\text{TL}}}}{2{\rho }_{avg,\text{TL}}}\end{array}$`

where:

• pA,TL and pB,TL are the pressures at ports A2 and B2, respectively.

• pTL is internal thermal liquid pressure at which the heat transfer is calculated.

• ${\stackrel{˙}{m}}_{A,TL}$ and ${\stackrel{˙}{m}}_{B,TL}$ are the mass flow rates into ports A2 and B2, respectively.

• ρavg,TL is the average thermal liquid density over all segments.

• ${\stackrel{˙}{m}}_{thres,TL}$ is the laminar threshold for pressure loss, approximated as 1e-4 of the nominal mass flow rate. The block calculates the pressure loss coefficient, KTL, so that pA,TLpB,TL matches the nominal pressure loss at the nominal mass flow rate.

The pressure losses on the moist air side are

`$\begin{array}{l}{p}_{A,MA}-{p}_{MA}=\frac{{K}_{MA}}{2}\frac{{\stackrel{˙}{m}}_{A,MA}\sqrt{{\stackrel{˙}{m}}^{2}{}_{A,MA}+{\stackrel{˙}{m}}^{2}{}_{thres,MA}}}{2{\rho }_{avg,2P}}\\ {p}_{B,MA}-{p}_{MA}=\frac{{K}_{MA}}{2}\frac{{\stackrel{˙}{m}}_{B,MA}\sqrt{{\stackrel{˙}{m}}^{2}{}_{B,MA}+{\stackrel{˙}{m}}^{2}{}_{thres,MA}}}{2{\rho }_{avg,MA}}\end{array}$`

where:

• pA,MA and pB,MA are the pressures at ports A2 and B2, respectively.

• pMA is internal moist air pressure at which the heat transfer is calculated.

• ${\stackrel{˙}{m}}_{A,MA}$ and ${\stackrel{˙}{m}}_{B,MA}$ are the mass flow rates into ports A2 and B2, respectively.

• ρavg,MA is the average moist air density over all segments.

• ${\stackrel{˙}{m}}_{thres,MA}$ is the laminar threshold for pressure loss, approximated as 1e-4 of the nominal mass flow rate. The block calculates the pressure loss coefficient, KMA, so that pA,MApB,MA matches the nominal pressure loss at the nominal mass flow rate.

### Thermal Liquid Mass and Energy Conservation

The mass conservation for the overall thermal liquid flow is

`$\left(\frac{d{p}_{TL}}{dt}\sum _{segments}\left(\frac{\partial {\rho }_{seg,TL}}{\partial p}\right)+\sum _{segments}\left(\frac{d{T}_{seg,TL}}{dt}\frac{\partial {\rho }_{seg,TL}}{\partial T}\right)\right)\frac{{V}_{TL}}{N}={\stackrel{˙}{m}}_{A,TL}+{\stackrel{˙}{m}}_{B,TL},$`

where:

• $\frac{\partial {\rho }_{seg,TL}}{\partial p}$ is the partial derivative of density with respect to pressure for the segment.

• $\frac{\partial {\rho }_{seg,TL}}{\partial T}$ is the partial derivative of density with respect to temperature for the segment.

• Tseg,TL is the temperature for the segment.

• VTL is the total thermal liquid volume.

The summation is over all segments.

Note

Although the thermal liquid flow is divided into N=3 segments for heat transfer calculations, all segments are assumed to be at the same internal pressure, pTL. That is why pTL is outside of the summation.

The energy conservation equation for each segment is

`$\begin{array}{l}\left(\frac{d{p}_{TL}}{dt}\frac{\partial {u}_{seg,TL}}{\partial p}+\frac{d{T}_{seg,TL}}{dt}\frac{\partial {u}_{seg,TL}}{\partial T}\right)\frac{{M}_{TL}}{N}+{u}_{seg,TL}\left({\stackrel{˙}{m}}_{seg,in,TL}-{\stackrel{˙}{m}}_{seg,out,TL}\right)=\\ {\Phi }_{seg,in,TL}-{\Phi }_{seg,out,TL}+{Q}_{seg,TL},\end{array}$`

where:

• $\frac{\partial {u}_{seg,TL}}{\partial p}$ is the partial derivative of specific internal energy with respect to pressure for the segment.

• $\frac{\partial {u}_{seg,TL}}{\partial T}$ is the partial derivative of specific internal energy with respect to temperature for the segment.

• MTL is the total thermal liquid mass.

• ${\stackrel{˙}{m}}_{seg,in,TL}$ and ${\stackrel{˙}{m}}_{seg,out,TL}$ are the mass flow rates into and out of the segment.

• Φseg,in,TL and Φseg,out,TL are the energy flow rates into and out of the segment.

The mass flow rates between segments are assumed to be linearly distributed between the values of${\stackrel{˙}{m}}_{A,TL}$ and ${\stackrel{˙}{m}}_{B,TL}$.

### Moist Air Mass and Energy Conservation

The mass conservation for the overall moist air mixture flow is

`$\begin{array}{l}\left(\frac{d{p}_{MA}}{dt}\sum _{segments}\left(\frac{\partial {\rho }_{seg,MA}}{\partial p}\right)+\sum _{segments}\left(\frac{d{T}_{seg,MA}}{dt}\frac{\partial {\rho }_{seg,MA}}{\partial T}+\frac{d{x}_{w,seg,MA}}{dt}\frac{\partial {\rho }_{seg,MA}}{\partial {x}_{w}}+\frac{d{x}_{g,seg,MA}}{dt}\frac{\partial {\rho }_{seg,MA}}{\partial {x}_{g}}\right)\right)\frac{{V}_{MA}}{N}=\\ {\stackrel{˙}{m}}_{A,MA}+{\stackrel{˙}{m}}_{B,MA}-\sum _{segments}\left({\stackrel{˙}{m}}_{w,seg,cond}\right),\end{array}$`

where:

• $\frac{\partial {\rho }_{seg,MA}}{\partial p}$ is the partial derivative of density with respect to pressure for the segment.

• $\frac{\partial {\rho }_{seg,MA}}{\partial T}$ is the partial derivative of density with respect to temperature for the segment.

• $\frac{\partial {\rho }_{seg,MA}}{\partial {x}_{w}}$ is the partial derivative of density with respect to specific humidity for the segment.

• $\frac{\partial {\rho }_{seg,MA}}{\partial {x}_{g}}$ is the partial derivative of density with respect to trace gas mass fraction for the segment.

• xw,seg,MA is the specific humidity, that is, the water vapor mass fraction, for the segment.

• xg,seg,MA is the trace gas mass fraction for the segment.

• VMA is the total moist air volume.

The summation is over all segments.

Note

Although the moist air flow is divided into N=3 segments for heat transfer calculations, all segments are assumed to be at the same internal pressure, pMA. That is why pMA is outside of the summation.

The energy conservation equation for each segment is

`$\begin{array}{l}\left(\frac{d{T}_{seg,MA}}{dt}\frac{\partial {u}_{seg,MA}}{\partial T}+\frac{d{x}_{w,seg,MA}}{dt}\frac{\partial {u}_{seg,MA}}{\partial {x}_{w}}+\frac{d{x}_{g,seg,MA}}{dt}\frac{\partial {u}_{seg,MA}}{\partial {x}_{g}}\right)\frac{{M}_{MA}}{N}+{u}_{seg,MA}\left({\stackrel{˙}{m}}_{seg,in,MA}-{\stackrel{˙}{m}}_{seg,out,MA}\right)=\\ {\Phi }_{seg,in,MA}-{\Phi }_{seg,out,MA}+{Q}_{seg,MA}-{\stackrel{˙}{m}}_{w,seg,cond}{h}_{l,wall},\end{array}$`

where:

• $\frac{\partial {u}_{seg,MA}}{\partial T}$ is the partial derivative of specific internal energy with respect to temperature for the segment.

• $\frac{\partial {u}_{seg,MA}}{\partial {x}_{w}}$ is the partial derivative of specific internal energy with respect to specific humidity for the segment.

• $\frac{\partial {u}_{seg,MA}}{\partial {x}_{g}}$ is the partial derivative of specific internal energy with respect to trace gas mass fraction for the segment.

• useg,2P is the specific internal energy for the segment.

• MMA is the total moist air mass.

• ${\stackrel{˙}{m}}_{seg,in,MA}$ and ${\stackrel{˙}{m}}_{seg,out,MA}$ are the mass flow rates into and out of the segment.

• Φseg,in,MA and Φseg,out,MA are the energy flow rates into and out of the segment.

The mass flow rates between segments are assumed to be linearly distributed between the values of${\stackrel{˙}{m}}_{A,MA}$ and ${\stackrel{˙}{m}}_{B,MA}$.

The water vapor mass conservation equation for each segment is

`$\begin{array}{l}\frac{d{x}_{w,seg,MA}}{dt}\frac{{M}_{MA}}{N}+{x}_{w,seg,MA}\left({\stackrel{˙}{m}}_{seg,in,MA}-{\stackrel{˙}{m}}_{seg,out,MA}\right)=\\ {\stackrel{˙}{m}}_{w,seg,in,MA}-{\stackrel{˙}{m}}_{w,seg,out,MA}-{\stackrel{˙}{m}}_{w,seg,cond},\end{array}$`

where ${\stackrel{˙}{m}}_{w,seg,in,MA}$ and ${\stackrel{˙}{m}}_{w,seg,out,MA}$ are the water vapor mass flow rates into and out of the segment.

The trace gas mass conservation equation for each segment is

`$\begin{array}{l}\frac{d{x}_{g,seg,MA}}{dt}\frac{{M}_{MA}}{N}+{x}_{g,seg,MA}\left({\stackrel{˙}{m}}_{seg,in,MA}-{\stackrel{˙}{m}}_{seg,out,MA}\right)=\\ {\stackrel{˙}{m}}_{g,seg,in,MA}-{\stackrel{˙}{m}}_{g,seg,out,MA},\end{array}$`

where ${\stackrel{˙}{m}}_{g,seg,in,MA}$ and ${\stackrel{˙}{m}}_{g,seg,out,MA}$ are the trace gas mass flow rates into and out of the segment.

## Ports

### Output

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Rate of heat transfer to thermal liquid, returned as a physical signal. Physical signals Q1 and Q2 are usually equal in value with opposite sign. However, if the Wall thermal mass parameter is set to `On`, then these two signals may have different values because the wall may absorb and release some of the heat being transferred.

Rate of heat transfer to moist air, returned as a physical signal. Physical signals Q1 and Q2 are usually equal in value with opposite sign. However, if the Wall thermal mass parameter is set to `On`, then these two signals may have different values because the wall may absorb and release some of the heat being transferred.

Water condensation rate in the moist air flow, returned as a physical signal. The condensate does not accumulate on the heat transfer surface.

### Conserving

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Inlet or outlet port associated with the thermal liquid.

Inlet or outlet port associated with the thermal liquid.

Inlet or outlet port associated with the moist air.

Inlet or outlet port associated with the moist air.

## Parameters

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### Configuration

Flow path alignment between the heat exchanger sides at nominal operating condition. The available flow arrangements are:

• ```Counter flow - Thermal Liquid 1 flows from A to B, Moist Air 2 flows from B to A``` — The flows run parallel to each other, in the opposite directions.

• `Parallel flow - Both fluids flow from A to B` — The flows run in the same direction.

• `Cross flow - Both fluids flow from A to B` — The flows run perpendicular to each other.

The choice between parallel flow and counter flow affects how the block determines the size of the heat exchanger. Counter flow is the most effective, therefore it will need the smallest size to meet the specified performance. Conversely, parallel flow is the least effective, therefore it will need the biggest size to meet the specified performance.

Flow direction at nominal condition (from A to B, or from B to A) affects only the model initialization, in case if you set the Initial condition specification parameter to ```Same as nominal operating condition```. If you set up different initial operating conditions, the flow directions can be different.

Once the size is determined, the choice between parallel and counter does not play a role in how the block calculates the heat transfer during simulation. Instead, the heat transfer depends on the flow directions during simulation. If you set the parameter to parallel flow but set up the model to run in counter flow (or the other way around), then the rate of heat transfer during simulation will not match the specified performance, even if the rest of the boundary conditions are the same.

If you set the parameter to cross flow, then the flow paths are modeled as perpendicular inside the heat exchanger, so the flow directions during simulation do not matter.

Enable or disable the effect of thermal mass on the heat transfer surface. Setting this parameter to `On` introduces additional dynamics to the simulation, so that it takes longer to reach steady state, but does not affect the results at steady-state simulation.

Mass of the heat transfer surface.

#### Dependencies

To enable this parameter, set Wall thermal mass to `On`.

Specific heat of the heat transfer surface.

#### Dependencies

To enable this parameter, set Wall thermal mass to `On`.

Flow area at the thermal liquid port A1.

Flow area at the thermal liquid port B1.

Flow area at the moist air port A2.

Flow area at the moist air port B2.

### Thermal Liquid 1

Select the nominal operating condition:

• `Heat transfer from thermal liquid to moist air` — The thermal liquid is being cooled and the moist air is being heated.

• `Heat transfer from moist air to thermal liquid` — The moist air is being cooled and the thermal liquid is being heated.

This choice relates only to specifying the nominal operating condition parameters. It does not mean that heat transfer can only happen in the specified direction during simulation.

Mass flow rate from port A1 to port B1 during the nominal operating condition.

Pressure drop from port A1 to port B1 during the nominal operating condition.

Pressure at the inlet of the thermal liquid of the heat exchanger during nominal operating condition.

Temperature at the inlet of the thermal liquid of the heat exchanger during the nominal operating condition.

Select whether to specify the performance of the heat exchanger at the nominal operating condition directly, by the rate of heat transfer, or indirectly, by the outlet condition.

Rate of heat transfer, depending on the nominal operating condition:

• If Nominal operating condition is ```Heat transfer from thermal liquid to moist air```, rate of heat transfer from the thermal liquid to the moist air during the nominal operating condition.

• If Nominal operating condition is ```Heat transfer from moist air to thermal liquid```, rate of heat transfer from the moist air to the thermal liquid during the nominal operating condition.

#### Dependencies

To enable this parameter, set Heat transfer capacity specification to ```Rate of heat transfer```.

Temperature at the outlet of the thermal liquid of the heat exchanger during the nominal operating condition.

#### Dependencies

To enable this parameter, set Heat transfer capacity specification to `Outlet condition`.

Total volume of thermal liquid inside the heat exchanger.

Select how to specify initial state of thermal liquid:

• `Same as nominal operating condition` — Start the simulation at the nominal operating condition.

• `Specify initial condition` — Specify a different set of initial conditions using additional parameters.

Thermal liquid pressure at the start of simulation.

#### Dependencies

To enable this parameter, set Initial condition specification to ```Specify initial condition```.

Thermal liquid temperature at the start of simulation.

#### Dependencies

To enable this parameter, set Initial condition specification to ```Specify initial condition```.

### Moist Air 2

Mass flow rate from port A2 to port B2 during the nominal operating condition.

Pressure drop from port A2 to port B2 during the nominal operating condition.

Pressure at the inlet of the moist air side of the heat exchanger during nominal operating condition.

Temperature at the inlet of the moist air side of the heat exchanger during the nominal operating condition.

Select quantity used to describe the moisture level at the inlet during the nominal operating condition: relative humidity, specific humidity, water vapor mole fraction, or humidity ratio.

Relative humidity at the inlet of the moist air side of the heat exchanger during the nominal operating condition.

#### Dependencies

To enable this parameter, set Inlet moisture specification to `Relative humidity`.

Specific humidity, defined as the mass fraction of water vapor in a moist air mixture, at the inlet of the moist air side of the heat exchanger during the nominal operating condition.

#### Dependencies

To enable this parameter, set Inlet moisture specification to `Specific humidity`.

Mole fraction of water vapor in a moist air mixture at the inlet of the moist air side of the heat exchanger during the nominal operating condition.

#### Dependencies

To enable this parameter, set Inlet moisture specification to `Mole fraction`.

Humidity ratio, defined as the mass ratio of water vapor to dry air and trace gas, at the inlet of the moist air side of the heat exchanger during the nominal operating condition.

#### Dependencies

To enable this parameter, set Inlet moisture specification to `Humidity ratio`.

Select quantity used to describe the trace gas level at the inlet during the nominal operating condition: mass fraction or mole fraction.

Mass fraction of trace gas in a moist air mixture at the inlet of the moist air side of the heat exchanger during the nominal operating condition.

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 Inlet trace gas specification to `Mass fraction`.

Mole fraction of trace gas in a moist air mixture at the inlet of the moist air side of the heat exchanger during the nominal operating condition.

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 Inlet trace gas specification to `Mole fraction`.

Total volume of moist air in the heat exchanger.

Select how to specify initial state of moist air:

• `Same as nominal operating condition` — Start the simulation at the nominal operating condition.

• `Specify initial condition` — Specify a different set of initial conditions using additional parameters.

Moist air pressure at the start of the simulation.

Moist air temperature at the start of simulation. If the value is a scalar, then the initial temperature is assumed uniform. If the value is a two-element vector, then the initial temperature is assumed to vary linearly between ports A2 and B2, with the first element corresponding to port A2 and the second element corresponding to port B2.

Select quantity used to describe the initial moisture level: relative humidity, specific humidity, water vapor mole fraction, or humidity ratio.

Moist air relative humidity at the start of simulation. If the value is a scalar, then the initial relative humidity is assumed uniform. If the value is a two-element vector, then the initial relative humidity is assumed to vary linearly between ports A2 and B2, with the first element corresponding to port A2 and the second element corresponding to port B2.

#### Dependencies

To enable this parameter, set Initial moisture specification to `Relative humidity`.

Moist air specific humidity, defined as the mass fraction of water vapor in a moist air mixture, at the start of simulation. If the value is a scalar, then the initial specific humidity is assumed uniform. If the value is a two-element vector, then the initial specific humidity is assumed to vary linearly between ports A2 and B2, with the first element corresponding to port A2 and the second element corresponding to port B2.

#### Dependencies

To enable this parameter, set Initial moisture specification to `Specific humidity`.

Mole fraction of water vapor in a moist air mixture at the start of simulation. If the value is a scalar, then the initial mole fraction is assumed uniform. If the value is a two-element vector, then the initial mole fraction is assumed to vary linearly between ports A2 and B2, with the first element corresponding to port A2 and the second element corresponding to port B2.

#### Dependencies

To enable this parameter, set Initial moisture specification to `Mole fraction`.

Moist air humidity ratio, defined as the mass ratio of water vapor to dry air and trace gas, at the start of simulation. If the value is a scalar, then the initial humidity ratio is assumed uniform. If the value is a two-element vector, then the initial humidity ratio is assumed to vary linearly between ports A2 and B2, with the first element corresponding to port A2 and the second element corresponding to port B2.

#### Dependencies

To enable this parameter, set Initial moisture specification to `Humidity ratio`.

Select quantity used to describe the trace gas level at the start of simulation: mass fraction or mole fraction.

Mass fraction of trace gas in a moist air mixture at the start of simulation. If the value is a scalar, then the initial mass fraction is assumed uniform. If the value is a two-element vector, then the initial mass fraction is assumed to vary linearly between ports A2 and B2, with the first element corresponding to port A2 and the second element corresponding to port B2.

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`.

Mole fraction of trace gas in a moist air mixture at the start of simulation. If the value is a scalar, then the initial mole fraction is assumed uniform. If the value is a two-element vector, then the initial mole fraction is assumed to vary linearly between ports A2 and B2, with the first element corresponding to port A2 and the second element corresponding to port B2.

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 point of condensation. Condensation occurs above this value. In most cases, this value is 1, that is, 100%. A value greater than 1 indicates a supersaturated vapor.

### Correlation Coefficients

Proportionality constant in the correlation of Nusselt number as a function of Reynolds number and Prandtl number for thermal liquid. The default value is based on the Colburn equation.

Reynolds number exponent in the correlation of Nusselt number as a function of Reynolds number and Prandtl number for thermal liquid.

Prandtl number exponent in the correlation of Nusselt number as a function of Reynolds number and Prandtl number for thermal liquid.

Proportionality constant in the correlation of Nusselt number as a function of Reynolds number and Prandtl number for moist air. The default value is based on the Colburn equation.

Reynolds number exponent in the correlation of Nusselt number as a function of Reynolds number and Prandtl number for moist air. The default value is based on the Colburn equation.

Prandtl number exponent in the correlation of Nusselt number as a function of Reynolds number and Prandtl number for moist air. The default value is based on the Colburn equation.

## Version History

Introduced in R2022a