Two phase iconTwo phase with an incondensable gas (low incondensable gas mass fraction)

The Flownex two phase with incondensable gas capability is used where the effects of incondensable gasses are not negligible, but the bulk fluid remains the two phase fluid. Typical industry systems include power conversion cycles (condensers), off-gas systems as well as systems in which air ingresses (i.e unwanted air ingress). The two phase with incondensable capabilities enables complete cycle simulations with fluid properties ranging from sub cooled liquids, two phase liquid and vapour/gas mixtures through to super-heated gasses and pure incondensable gas, all of which is accounted for using a single Flownex fluid. The gas phase of the mixture is made up of the two phase vapour component and the incondensable gas component, the gas component mixture properties being calculated according to their various mass fractions. The Flownex two phase with incondensable gas capability is valid for the two phase fluid’s subcritical region.

As with Flownex’s pure two phase capability, the two phase with incondensable gas also uses the homogeneous model for simulating flow. Phase separation and level tracking in containers is also accounted for while the incondensable gas and two phase vapour partial pressures is determined throughout the network. The liquid and gas phase mixture temperature in the container is based on the two phase vapour components’ saturation temperature at the two phase vapour component’s partial pressure. This is based on the mixture phases being in thermal equilibrium.

As with Flownex’s pure two phase capability, the two phase with incondensable capability includes:

  • Heat transfer
  • Boiling
  • Condensation
  • Phase separation
  • Flow regime approximation
  • Critical mass flux (choked flow)

 

The gas component mixture properties, determined according to the incondensable gas and two phase vapour mass fractions of the mixture, is used in calculating the above mentioned phenomena.

As with the pure two phase fluids, most Flownex® library components can be used for two phase with incondensable gas simulations, enabling the user to develop simulation models with various modelling approaches and varying degrees of detail and accuracy.

 

Psychrometry (low two phase mass fraction)

The Flownex psychrometry capability is used where the effects of a two phase fluid (either in liquid/vapour mixture form or as vapour only) present in an incondensable gas are not negligible. Typical industry systems include HVAC (Heating, Ventilation and Air Conditioning), off-gas systems as well as compressed air systems where condensation is of importance. The psychrometry capability enables complete system simulations with fluid properties ranging from vapour/gas mixtures, droplet or condensation formation through to dry gas (pure incondensable gas) simulations, all of which is accounted for using a single Flownex fluid. Flownex uses a homogeneous model to allow flow simulation in the event of droplets (liquid phase) being present in the fluid. The gas phase of the mixture is made up of the two phase vapour component and the incondensable gas component, the gas component mixture properties being calculated according to their various mass fractions. The Flownex psychrometry capability is valid for the two phase fluid’s subcritical region.

The Flownex® psychrometry capability allows use of most of the Flownex® library components, enabling the user to develop simulation models with various modelling approaches and varying degrees of detail and accuracy. Functionalities available to the user, for example for HVAC systems employing two phase water and air as the incondensable gas are:

  • Relative humidity and humidity ratio results throughout the network.
  • Wet bulb temperature results throughout the network.
  • Condensation due to pressure and temperature variations (for example compression processes and heat exchange).
  • Evaporation due to pressure and temperature variations.
  • Condensate extraction.
  • Critical mass flux (choked flow in compressed air systems).

Flownex®’s psychrometry capability enables the user to perform psychrometric calculations for complete systems at varying pressure levels including compressed air and high pressure systems in which water vapour plays an important role.