Buildings.MassExchangers

Package Content

Name	Description
Examples	Collection of models that illustrate model use and test models
HumidifierPrescribed	Ideal electric heater or cooler, no losses, no dynamics

Buildings.MassExchangers.HumidifierPrescribed

Information

Model for an air humidifier or dehumidifier.

This model adds (or removes) moisture from the air stream. The amount of exchanged moisture is equal to m_flow = u m0_flow. The input signal u and the nominal moisture flow rate added to the air stream m0_flow can be positive or negative. If the product u * m0_flow are positive, then moisture is added to the air stream, otherwise it is removed.

If the connector T_in is left unconnected, the value set by the parameter T is used for temperature of the water that is added to the air stream.

Note that if the mass flow rate tends to zero, the moisture difference over this component tends to infinity for non-zero m_flow, so add proper control when using this component.

Parameters

Type	Name	Default	Description
replaceable package Medium		PartialMedium	Medium in the component
MassFlowRate	m0_flow		Water mass flow rate at u=1, positive for humidification [kg/s]
Temperature	T	293.15	Temperature of water that is added to the fluid stream (used only if T_in is unconnected) [K]
Initialization
MassFlowRate	m_flow		Mass flow rate from port_a to port_b (m_flow > 0 is design flow direction) [kg/s]
Pressure	dp		Pressure difference between port_a and port_b [Pa]
Advanced
Temp	flowDirection	Modelica_Fluid.Types.FlowDir...	Unidirectional (port_a -> port_b) or bidirectional flow component

Connectors

Type	Name	Description
FluidPort_a	port_a	Fluid connector a (positive design flow direction is from port_a to port_b)
FluidPort_b	port_b	Fluid connector b (positive design flow direction is from port_a to port_b)
input RealInput	T_in	Temperature of water added to the fluid stream
input RealInput	u

Modelica definition

model HumidifierPrescribed 
  "Ideal electric heater or cooler, no losses, no dynamics" 
  extends Fluids.Interfaces.PartialStaticTwoPortHeatMassTransfer;
  extends Buildings.BaseClasses.BaseIcon;
  
  parameter Modelica.SIunits.MassFlowRate m0_flow 
    "Water mass flow rate at u=1, positive for humidification";
  parameter Modelica.SIunits.Temperature T = 293.15 
    "Temperature of water that is added to the fluid stream (used only if T_in is unconnected)";
  Modelica.Blocks.Interfaces.RealInput T_in(
    redeclare type SignalType = Modelica.SIunits.Temperature) 
    "Temperature of water added to the fluid stream";
  Modelica.Blocks.Interfaces.RealInput u;
protected 
  constant Modelica.SIunits.MassFraction[Medium.nXi] XiWat = {1} 
    "Mass fraction of water";
  Modelica.SIunits.MassFlowRate mWat_flow "Water flow rate";
equation 
  if cardinality(T_in)==0 then
    T_in = T;
  end if;
  
  dp = 0;
  mWat_flow = u * m0_flow;
  Q_flow = Medium.enthalpyOfLiquid(T_in) * mWat_flow;
  for i in 1:Medium.nXi loop
     mXi_flow[i] = if ( i == Medium.Water) then  mWat_flow else 0;
  end for;
end HumidifierPrescribed;