modelMixingVolumeMoistAir

Information

Model for an ideally mixed fluid volume and the ability to store mass and energy. The volume is fixed, and latent and sensible heat can be exchanged.

This model represents the same physics as AixLib.Fluid.MixingVolumes.MixingVolume, but in addition, it allows adding or subtracting water to the control volume. The mass flow rate of the added or subtracted water is specified at the port mWat_flow. Adding mWat_flow itself does not affect the energy balance in this model. Hence, the enthalpy that is added or removed with the flow of mWat_flow needs to be added to the heat port heatPort.

To increase the numerical robustness of the model, the constant prescribedHeatFlowRate can be set by the user. This constant only has an effect if the model has exactly two fluid ports connected, and if it is used as a steady-state model. Use the following settings:

• Set prescribedHeatFlowRate=true if the only means of heat transfer at the heatPort is a prescribed heat flow rate that is not a function of the temperature difference between the medium and an ambient temperature. Examples include an ideal electrical heater, a pump that rejects heat into the fluid stream, or a chiller that removes heat based on a performance curve. If the heatPort is not connected, then set prescribedHeatFlowRate=true as in this case, heatPort.Q_flow=0.
• Set prescribedHeatFlowRate=false if there is heat flow at the heatPort computed as K * (T-heatPort.T), for some temperature T and some conductance K, which may itself be a function of temperature or mass flow rate.
  If there is a combination of K * (T-heatPort.T) and a prescribed heat flow rate, for example a solar collector that dissipates heat to the ambient and receives heat from the solar radiation, then set prescribedHeatFlowRate=false.

Options

The parameter mSenFac can be used to increase the thermal mass of this model without increasing its volume. This way, species concentrations are still calculated correctly even though the thermal mass increases. The additional thermal mass is calculated based on the density and the value of the function HeatCapacityCp of the medium state state_default.
This parameter can for instance be useful in a pipe model when the developer wants to lump the pipe thermal mass to the fluid volume. By default mSenFac = 1, hence the mass is unchanged. For higher values of mSenFac, the mass will be scaled proportionally.

Set the parameter use_C_flow = true to enable an input connector for the trace substance flow rate. This allows to directly add or subtract trace substances such as CO2 to the volume. See AixLib.Fluid.Sensors.Examples.PPM for an example.

Parameters

Components

Revisions

• October 19, 2017, by Michael Wetter:
  Set initialize_p to final so that it does not appear as a user-selectable parameter. This is done because initialize_p has been changed from a constant to a parameter for Buildings, issue 1013.
• April 11, 2017, by Michael Wetter:
  Changed comment of heat port, as this needs to be the total heat flow rate in order to be able to use this model for modeling steam humidifiers and adiabatic humidifiers.
  Removed blocks QSen_flow and QLat_flow.
  This is for issue Buildings #704.
• January 22, 2016 by Michael Wetter:
  Removed assignment of sensibleOnly in steBal as this constant is no longer used.
• January 19, 2016, by Michael Wetter:
  Updated documentation due to the addition of an input for trace substance in the mixing volume. This is for issue 372.
• February 11, 2014 by Michael Wetter:
  Redesigned implementation of latent and sensible heat flow rates as port of the correction of issue #197.
• December 18, 2013 by Michael Wetter:
  Changed computation of s to allow this model to also be used with AixLib.Media.Water.
• October 21, 2013 by Michael Wetter:
  Removed dublicate declaration of medium model.
• September 27, 2013 by Michael Wetter:
  Reformulated assignment of i_w to avoid a warning in OpenModelica.
• September 17, 2013 by Michael Wetter:
  Changed model to no longer use the obsolete model AixLib.Fluid.MixingVolumes.BaseClasses.PartialMixingVolumeWaterPort.
• July 30, 2013 by Michael Wetter:
  Changed connector mXi_flow[Medium.nXi] to a scalar input connector mWat_flow in the conservation equation model. The reason is that mXi_flow does not allow to compute the other components in mX_flow and therefore leads to an ambiguous use of the model. By only requesting mWat_flow, the mass balance and species balance can be implemented correctly.
• April 18, 2013 by Michael Wetter:
  Removed the use of the deprecated cardinality function. Therefore, all input signals must be connected.
• February 7, 2012 by Michael Wetter:
  Revised base classes for conservation equations in AixLib.Fluid.Interfaces.
• February 22, by Michael Wetter:
  Improved the code that searches for the index of 'water' in the medium model.
• May 29, 2010 by Michael Wetter:
  Rewrote computation of index of water substance. For the old formulation, Dymola 7.4 failed to differentiate the model when trying to reduce the index of the DAE.
• August 7, 2008 by Michael Wetter:
  First implementation.