28th Symposium of AER on VVER Reactor Physics and Reactor Safety (2018, Olomouc, Czechia)
Nuclear applications of computational fluid dynamics (CFD)
Ladislav Vyskočil, Václav Železný (ÚJV Řež)
This paper presents an attempt to use multiphase CFD code for the prediction of the Departure from Nucleate Boiling (DNB) type of Critical Heat Flux (CHF). Numerical simulations of DNB in boiling flow in vertical tube were performed with the Ansys CFX 18 code. This code can simulate multiphase flow by solving three balance equations for each phase. Boiling on the heated wall can be simulated with Kurul and Podowski model. A set of mathematical models of physical phenomena in boiling bubbly flow was selected and successfully tested on the DEBORA experiments with subcooled boiling flow. The same set of models was then used in the simulations of DNB cases. Simulated cases were based on data from the 2006 CHF look-up table by D. C. Groeneveld.
It was found out that the local criterion for DNB prediction can be based on the following parameters calculated with the CFD code on the wall: void fraction, wall superheating and wall shear stress. The proposed method of DNB detection was so far tested on 16 MPa pressure level on many cases covering a large range of parameters (mass flux 1000 – 7000 kg/m2/s and exit equilibrium quality -0.4 – 0) and it worked with +-10% accuracy in almost all cases.
Presented work was carried out within the Technology Agency of the Czech Republic (TA ČR) project TH02020360 „Modeling of the critical heat flux with computational fluid dynamics codes“.