Extension of the wall boiling model by using the MUSIG approach

The report describes the capabilities of CFD simulatin wall boiling coupled with a population balance model. For the demonstration DEBORA tests were used. Instead of water at high pressure in the DEBORA tests Dichlorodifluoromethane (R12) was used as the working fluid. Similar conditions in terms of the relevant non-dimensional numbers have been realized. This facilitated measurements of radial profiles for gas volume fraction, gas velocity, liquid temperature and bubble size.
Essential for the momentum, mass and energy exchange between the phases is an adequate description of the interfacial area or respectively the bubble size. In the present work a population balance approach coupled to a wall boiling model is used, where bubbles are generated at the wall with a certain size that subsequently evolves due to both condensation / evaporation and coalescence / fragmentation processes. The paper shows the potential of this approach which is able to describe the observed bubble size increase caused by bubble coalescence after leaving the wall as well as the change of gas fraction profile from wall to core peaking with increasing inlet temperature respective decreasing liquid subcooling and consequently enhanced vapour generation.