.AixLib.Media.Specialized.Water.TemperatureDependentDensity

Information

This medium package models liquid water.

The mass density is computed using a 3rd order polynomial, which yields the density as a function of temperature as shown in the figure below. Note, however, that computing density as a function of temperature can lead to considerably slower computing time compared to using AixLib.Media.Water in which the density is a constant. We therefore recommend to use AixLib.Media.Water for typical building energy simulations.

For the specific heat capacities at constant pressure and at constant volume, a constant value of 4184 J/(kg K), which corresponds to 20°C is used. The figure below shows the relative error of the specific heat capacity that is introduced by this simplification. Using a constant value for the specific heat capacity allows to compute temperature from enthalpy without having to solve an implicit equation, and therefore leads to faster simulation.

Thermal conductivity is calculated as a function of temperature as shown in the figure below. The correlation used to calculate the thermal conductivity is

λ(T) = λ(298.15 K) ⋅ (-1.48445+4.12292⋅(T/298.15)-1.63866⋅(T/298.15)²),

where λ(298.15 K) = 0.6065 W/(m ⋅ K) is the adopted standard value of the thermal conductivity of water at 298.15 K and 0.1 MPa.

Dynamic viscosity is calculated as the product of density and kinematic viscosity, both temperature dependent. However, the kinematic viscosity has its own temperature dependent correlation, implemented at AixLib.Media.Specialized.Water.TemperatureDependentDensity.kinematicViscosity. Results of the kinematic viscosity as a function of temperature are shown in the figure below.

The enthalpy is computed using the convention that h=0 if T=0 °C.

Limitations

Phase changes are not modeled.

Contents

Name	Description
FluidConstants
ThermodynamicState	Thermodynamic state variables
BaseProperties	Base properties
density	Return the density
dynamicViscosity	Return the dynamic viscosity
specificEnthalpy	Return the specific enthalpy
enthalpyOfLiquid	Return the specific enthalpy of liquid
specificInternalEnergy	Return the specific enthalpy
specificEntropy	Return the specific entropy
specificGibbsEnergy	Return the specific Gibbs energy
specificHelmholtzEnergy	Return the specific Helmholtz energy
isentropicEnthalpy	Return the isentropic enthalpy
isobaricExpansionCoefficient	Return the isobaric expansion coefficient
isothermalCompressibility	Return the isothermal compressibility factor
density_derp_T	Return the partial derivative of density with respect to pressure at constant temperature
density_derT_p	Return the partial derivative of density with respect to temperature at constant pressure
density_derX	Return the partial derivative of density with respect to mass fractions at constant pressure and temperature
specificHeatCapacityCp	Return the specific heat capacity at constant pressure
specificHeatCapacityCv	Return the specific heat capacity at constant volume
thermalConductivity	Return the thermal conductivity
pressure	Return the pressure
temperature	Return the temperature
molarMass	Return the molar mass
setState_dTX	Return thermodynamic state from d, T, and X or Xi
setState_phX	Return the thermodynamic state as function of pressure p, specific enthalpy h and composition X or Xi
setState_pTX	Return the thermodynamic state as function of p, T and composition X or Xi
setState_psX	Return the thermodynamic state as function of p, s and composition X or Xi

Revisions

• April 5, 2022, by Michael Wetter:
  Corrected assignment of R_s in BaseProperties to avoid a unit error.
  This is for #1603.
• July 7, 2016, by Carles Ribas Tugores:
  Correct Documentation. This is for #487.
• June 6, 2015, by Michael Wetter:
  Set AbsolutePressure(start=p_default) and Temperature(start=T_default) to have to have conistent start values. See also revision notes of AixLib.Media.Water. This is for #266.
• May 1, 2015, by Michael Wetter:
  Added Inline=true for issue 227.
• February 25, 2015, by Michael Wetter:
  Removed stateSelect attribute on pressure as this caused AixLib.Examples.Tutorial.SpaceCooling.System3 to fail with the error message "differentiated if-then-else was not continuous".
• February 3, 2015, by Michael Wetter:
  Removed stateSelect.prefer for temperature. This is for #160.
• October 15, 2014, by Michael Wetter:
  Renamed from AixLib.Media.Water to AixLib.Media.Water.Detailed to allow addition of AixLib.Media.Water.Simple.
• September 12, 2014, by Michael Wetter:
  Set T(start=T_default) and p(start=p_default) in the ThermodynamicState record. Setting the start value for T is required to avoid an error due to conflicting start values when checking AixLib.Examples.VAVReheat.ClosedLoop in pedantic mode.
• December 18, 2013, by Michael Wetter:
  First implementation.