Model for a spray air washer with a prescribed outlet water
vapor mass fraction in kg/kg total air.

This model 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.

The output signal `mWat_flow ≥ 0`

is the moisture
added to the medium if the flow rate is from `port_a`

to
`port_b`

. If the flow is reversed, then ```
mWat_flow
= 0
```

. The outlet specific enthalpy at `port_b`

is
increased by the enthalpy of liquid water at *10*°C times the
mass of water that was added. Therefore, the temperature of the
leaving fluid is below the inlet temperature.

The outlet conditions at `port_a`

are not affected by
this model, other than for a possible pressure difference due to
flow friction.

If the parameter `energyDynamics`

is different from
`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

τ_{eff} = τ
|ṁ| ⁄ ṁ_{nom}

where *τ*_{eff} is the effective time constant for
the given mass flow rate *ṁ* and *τ* is the time
constant at the nominal mass flow rate *ṁ*_{nom}.
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. Set
`dp_nominal = 0`

to disable the flow friction
calculation.

For a model that uses a control signal *u ∈ [0, 1]* and
multiplies this with the nominal water mass flow rate, use Buildings.Fluid.Humidifiers.Humidifier_u

#### Limitations

This model only adds water vapor for the flow from
`port_a`

to `port_b`

. The water vapor of the
reverse flow is not affected by this model.

This model does not affect the enthalpy of the air. Therefore,
if water is added, the temperature will decrease, e.g., the
humidification is adiabatic.

- December 14, 2018, by Michael Wetter:

Restricted base class for medium to one that implements the
function `enthalpyOfLiquid`

.

This is for #1057.
- May 3, 2017, by Michael Wetter:

First implementation.

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