Evaporating and condensing flows

For many applications evaporation and condensation processes are important. Models are developed for wall boiling including the consideration of critical heat flux (CHF), for boiling flows caused by pressure decrease and for condensing flows.

The inhomogeneous MUSIG model was extended to allow the consideration of phase transfer (Lucas et al., 2011). Corresponding implementations were done together with ANSYS into the commercial CFD-code ANSYS-CFX and are available in the standard release.

Wall boiling Model

A new model for the simulation of bubble generation, growth and departure from the wall was developed basing on the micro-layer theory. The single bubble model considers the dynamic bubble geometry, contact angle and bubble inclination angle in flow boiling at different time periods.

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Critical heat flux

Boiling heat transfer is limited by the critical heat flux (CHF), also termed as boiling crisis. It leads to a rapid decrease of the heat transfer coefficient in temperature controlled heat transfer or to a significant jump in hea­ter surface temperature in power controlled heat transfer cases.

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Flashing flow

Flash boiling is a kind of phase change from liquid to vapour due to depressurization, which has a fundamental and decisive presence in many industrial and technical applications. For example, it can be encountered in flow through di­vergent nozzles, blow-off valves or cracks at pressurized liquid containers or in natural circulation cooling systems.

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Condensing flow

Basing the inhomogeneous MUSIG model which was extended for flows with phase transfer and the baseline closure models phase transfer models were implemented to allow the simulation of condensing flows.

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Publication on the extension of the inhomogeneous MUSIG model

• Lucas, D.; Frank, T.; Lifante, C.; Zwart, P.; Burns, A.
  Extension of the Inhomogeneous MUSIG model for bubble condensation.
  Nuclear Engineering and Design 241(2011), 4359-4367