Buildings.Fluid.HeatExchangers.CoolingTowers.BaseClasses

Information

This package contains base classes that are used to construct the models in Buildings.Fluid.HeatExchangers.CoolingTowers.

Extends from Modelica.Icons.BasesPackage (Icon for packages containing base classes).

Package Content

Name	Description
CoolingTower	Base class for cooling towers

Buildings.Fluid.HeatExchangers.CoolingTowers.BaseClasses.CoolingTower

Information

Base class for a steady-state cooling tower. The variable TAirHT is used to compute the heat transfer with the water side of the cooling tower. For a dry cooling tower, this is equal to the dry-bulb temperature. For a wet cooling tower, this is equal to the wet-bulb temperature.

Extends from Buildings.Fluid.Interfaces.TwoPortHeatMassExchanger (Partial model transporting one fluid stream with storing mass or energy), Buildings.BaseClasses.BaseIcon (Base icon).

Parameters

Type	Name	Default	Description
replaceable package Medium		PartialMedium	Medium in the component
Nominal condition
MassFlowRate	m_flow_nominal		Nominal mass flow rate [kg/s]
Pressure	dp_nominal		Pressure [Pa]
Initialization
MassFlowRate	m_flow.start	0	Mass flow rate from port_a to port_b (m_flow > 0 is design flow direction) [kg/s]
Pressure	dp.start	0	Pressure difference between port_a and port_b [Pa]
Assumptions
Boolean	allowFlowReversal	system.allowFlowReversal	= true to allow flow reversal, false restricts to design direction (port_a -> port_b)
Advanced
MassFlowRate	m_flow_small	1E-4*abs(m_flow_nominal)	Small mass flow rate for regularization of zero flow [kg/s]
Boolean	homotopyInitialization	true	= true, use homotopy method
Diagnostics
Boolean	show_V_flow	false	= true, if volume flow rate at inflowing port is computed
Boolean	show_T	true	= true, if actual temperature at port is computed (may lead to events)
Flow resistance
Boolean	from_dp	false	= true, use m_flow = f(dp) else dp = f(m_flow)
Boolean	linearizeFlowResistance	false	= true, use linear relation between m_flow and dp for any flow rate
Real	deltaM	0.1	Fraction of nominal flow rate where flow transitions to laminar
Dynamics
Nominal condition
Time	tau	30	Time constant at nominal flow (if energyDynamics <> SteadyState) [s]
Equations
Dynamics	energyDynamics	Modelica.Fluid.Types.Dynamic...	Formulation of energy balance
Dynamics	massDynamics	energyDynamics	Formulation of mass balance
Initialization
AbsolutePressure	p_start	Medium.p_default	Start value of pressure [Pa]
Temperature	T_start	Medium.T_default	Start value of temperature [K]
MassFraction	X_start[Medium.nX]	Medium.X_default	Start value of mass fractions m_i/m [kg/kg]
ExtraProperty	C_start[Medium.nC]	fill(0, Medium.nC)	Start value of trace substances

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)
output RealOutput	TLvg	Leaving water temperature

Modelica definition

partial model CoolingTower "Base class for cooling towers"
  extends Buildings.Fluid.Interfaces.TwoPortHeatMassExchanger(
    redeclare final Buildings.Fluid.MixingVolumes.MixingVolume vol,
    show_T=true);
  extends Buildings.BaseClasses.BaseIcon;
  Modelica.Blocks.Interfaces.RealOutput TLvg "Leaving water temperature";
  Modelica.SIunits.HeatFlowRate Q_flow = QWat_flow.y 
    "Heat input into water circuit";
  Modelica.SIunits.TemperatureDifference TAppAct(min=0, nominal=1, displayUnit="K") 
    "Actual approach temperature";

protected 
  Modelica.SIunits.Temperature TAirHT 
    "Air temperature that is used to compute the heat transfer with the water";

  Modelica.Thermal.HeatTransfer.Sources.PrescribedHeatFlow preHea 
    "Prescribed heat flow";
  Modelica.Blocks.Sources.RealExpression QWat_flow(y=m_flow*(
        Medium.specificEnthalpy(Medium.setState_pTX(
        p=port_b.p,
        T=TAirHT + TAppAct,
        X=inStream(port_b.Xi_outflow))) - inStream(port_a.h_outflow))) 
    "Heat input into water";
  Modelica.Thermal.HeatTransfer.Sensors.TemperatureSensor T_Vol 
    "Water temperature in volume, or leaving water temperature";

equation 
  connect(preHea.port, vol.heatPort);
  connect(QWat_flow.y, preHea.Q_flow);
  connect(T_Vol.port, vol.heatPort);
  connect(T_Vol.T, TLvg);

end CoolingTower;