WOLFRAM SYSTEMMODELER

PsychrometricData

Produces plot data for psychrometric charts

Wolfram Language

In[1]:=
SystemModel["Modelica.Media.Examples.PsychrometricData"]
Out[1]:=

Information

This information is part of the Modelica Standard Library maintained by the Modelica Association.

This model produces psychrometric data from the moist air model in this library to be plotted in charts. The two most common chart varieties are the Mollier Diagram and the Psychrometric Chart. The first is widely used in some European countries while the second is more common in the Anglo-American world. Specific enthalpy is plotted over absolute humidity in the Mollier Diagram, it is the other way round in the Psychrometric Chart.
It must be noted that the relationship of both axis variables is not right-angled, the absolute humidity follows a slope which equals the enthalpy of vaporization at 0 °C. For better reading and in order to reduce the fog region the humidity axis is rotated to obtain a right-angled plot. Both charts usually contain additional information as isochores or auxiliary scales for e.g., heat ratios. Those information are omitted in this model and the charts below. Other important features of psychrometric chart data are that all mass specific variables (like absolute humidity, specific enthalpy etc.) are expressed in terms of kg dry air and that their baseline of 0 enthalpy is found at 0 °C and zero humidity.


Legend: blue - constant specific enthalpy, red - constant temperature, black - constant relative humidity

The model provides data for lines of constant specific enthalpy, temperature and relative humidity in a Mollier Diagram or Psychrometric Chart as they were used for the figures above. For limitations and ranges of validity please refer to the MoistAir package description. Absolute humidity x is increased with time in this model. The specific enthalpies adjusted for plotting are then obtained from:

  • y_h: constant specific enthalpy
  • y_T: constant temperature
  • y_phi: constant relative humidity

Parameters (18)

p_const

Value: 1e5

Type: Pressure (Pa)

Description: Pressure

n_T

Value: 11

Type: Integer

Description: Number of isotherms

T_min

Value: 253.15

Type: Temperature (K)

Description: Lowest isotherm

T_step

Value: 10

Type: Temperature (K)

Description: Temperature step between two isotherms

n_h

Value: 16

Type: Integer

Description: Number of lines with constant specific enthalpy

h_min

Value: -20e3

Type: SpecificEnthalpy (J/kg)

Description: Lowest line of constant enthalpy

h_step

Value: 1e4

Type: SpecificEnthalpy (J/kg)

Description: Enthalpy step between two lines of constant enthalpy

n_phi

Value: 10

Type: Integer

Description: Number of lines with constant relative humidity

phi_min

Value: 0.1

Type: Real

Description: Lowest line of constant humidity

phi_step

Value: 0.1

Type: Real

Description: Step between two lines of constant humidity

x_min

Value: 0.00

Type: MassFraction

Description: Minimum diagram absolute humidity

x_max

Value: 0.03

Type: MassFraction

Description: Maximum diagram absolute humidity

t

Value: 1

Type: Time (s)

Description: Simulation time

T_const

Value: array(T_min - T_step + i * T_step for i in 1:n_T)

Type: Temperature[n_T] (K)

Description: Constant temperatures

h_const

Value: array((i - 1) * h_step + h_min for i in 1:n_h)

Type: SpecificEnthalpy[n_h] (J/kg)

Description: Constant enthalpies

phi_const

Value: array((i - 1) * phi_step + phi_min for i in 1:n_phi)

Type: Real[n_phi]

Description: Constant relative humidities

diagSlope

Value: Medium.enthalpyOfVaporization(273.15)

Type: Real

Description: Rotation of diagram that zero degrees isotherm becomes horizontal outside the fog region

x_start

Value: x_min

Type: MassFraction

Description: Initial absolute humidity in kg water/kg dry air

Components (2)

medium_T

Type: BaseProperties[n_T]

Description: Medium properties for const T

medium_phi

Type: BaseProperties[n_phi]

Description: Medium properties for const phi