AixLib.Fluid.HeatExchangers.PrescribedOutlet

# .AixLib.Fluid.HeatExchangers.PrescribedOutlet

Ideal heater, cooler, humidifier or dehumidifier with prescribed outlet conditions

## Information

Model that allows specifying the temperature and mass fraction of the fluid that leaves the model from `port_b`.

This model forces the outlet temperature at `port_b` to be equal to the temperature of the input signal `TSet`, subject to optional limits on the heating or cooling capacity `QMax_flow ≥ 0` and `QMin_flow ≤ 0`. Similarly than for the temperature, this model also forces the outlet water mass fraction at `port_b` to be no lower than the input signal `X_wSet`, subject to optional limits on the maximum water vapor mass flow rate that is added, as described by the parameter `mWatMax_flow`. By default, the model has unlimited capacity, but control of temperature and humidity can be subject to capacity limits, or be disabled.

The output signal `Q_flow` is the heat added (for heating) or subtracted (for cooling) to the medium if the flow rate is from `port_a` to `port_b`. If the flow is reversed, then `Q_flow=0`.

The outlet conditions at `port_a` are not affected by this model.

If the parameter `energyDynamics` is not equal to `Modelica.Fluid.Types.Dynamics.SteadyState`, the component models the dynamic response using a first order differential equation. The time constant of the component is equal to the parameter `tau`. This time constant is adjusted based on the mass flow rate using

τeff = τ |ṁ| ⁄ ṁnom

where τeff is the effective time constant for the given mass flow rate ṁ and τ is the time constant at the nominal mass flow rate ṁnom. This type of dynamics is equal to the dynamics that a completely mixed control volume would have.

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

For a model that uses a control signal u ∈ [0, 1] and multiplies this with the nominal heating or cooling power, use AixLib.Fluid.HeatExchangers.HeaterCooler_u

#### Limitations

This model only adds or removes heat or water vapor for the flow from `port_a` to `port_b`. The enthalpy of the reverse flow is not affected by this model.

If this model is used to cool air below the dew point temperature, the water mass fraction will not change.

Note that for `use_TSet = false`, the enthalpy of the leaving fluid will not be changed, even if moisture is added. The enthalpy added (or removed) by the change in humidity is neglected. To properly account for change in enthalpy due to humidification, use instead AixLib.Fluid.Humidifiers.SprayAirWasher_X.

#### Validation

The model has been validated against the analytical solution in the examples AixLib.Fluid.HeatExchangers.Validation.PrescribedOutlet and AixLib.Fluid.HeatExchangers.Validation.PrescribedOutlet_dynamic.

## Revisions

- March 3, 2022, by Michael Wetter:
  Removed `massDynamics`.
  This is for issue 1542.
- May 3, 2017, by Michael Wetter:
  Updated protected model for #763.
- December 1, 2016, by Michael Wetter:
  Updated model as `use_dh` is no longer a parameter in the pressure drop model.
  This is for #480.
- November 11, 2014, by Michael Wetter:
  Revised implementation.
- March 19, 2014, by Christoph Nytsch-Geusen:
  First implementation.

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