.FCSys.Characteristics.BaseClasses.Characteristic.eta

Fluidity (η) as a function of temperature

Information

Fluidity is defined as the reciprocal of dynamic viscosity (see http://en.wikipedia.org/wiki/Viscosity#Fluidity).

Although specific volume is an input to this function, the result is independent of specific volume. According to Present [Present1958], this independence very accurately matches the measured fluidity of gases. However, the fluidity varies by species and generally falls more rapidly with temperature than indicated [Present1958, p. 41].

This function is based on the kinetic theory of gases under the following assumptions [Present1958]:

  1. The particles are smooth and rigid but elastic spheres with identical radii. This is the "billiard-ball" assumption, and it implies that the collisions are instantaneous and conserve kinetic energy.
  2. Between collisions, particles have no influence on one another.
  3. The mean free path, or average distance a particle travels between collisions, is much larger than the diameter of a particle.
  4. The properties carried by a particle depend only on those of the last particle with which it collided.
  5. The speeds of the particles follow the Maxwell-Boltzmann distribution.

Interface

function eta
  extends Modelica.Icons.Function;
  input Q.TemperatureAbsolute T = 298.15*U.K "Temperature" annotation(
    Dialog(__Dymola_label = "<html><i>T</i></html>"));
  input Q.VolumeSpecific v = 298.15*U.K/p0 "Specific volume" annotation(
    Dialog(__Dymola_label = "<html><i>v</i></html>"));
  output Q.Fluidity eta "Fluidity" annotation(
    Dialog(__Dymola_label = "<html>&eta;</html>"));
end eta;
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