The effects of surface orientation, heater size, wettability, and subcooling on the critical heat flux enhancement in pool boiling

Enhancing Critical Heat Flux (CHF) in pool boiling significantly extends the safety limit in the nuclear system, especially under the In-Vessel Retention-Reactor Vessel Cooling (IVR-ERVC) severe accident management strategy to avoid the failure of the lower head reactor pressure vessel. In this work, the lattice Boltzmann method (LBM) is employed to simulate the effect of surface orientation, wettability, geometric size, and subcooling of the downward-facing lower head on the CHF enhancement. It was found that for the downward-facing surface, the CHF increases with increasing surface orientation, while a vertical surface gives a slightly lower CHF compared to a near-vertical surface. Besides, the CHF for a downward facing surface increases with increasing wettability. The CHF performance of the near-vertical and vertical surfaces exhibits the largest improvement with decreasing surface contact angle. Moreover, it reveals that with an increased radius of the lower head, the CHF decreases for all curved surfaces, especially obvious for the inclination angle smaller than 90∘. For a vertical surface, increasing the length of the heated surface has no obvious improvement on the CHF. This study also provides a discussion regarding the effect of subcooling on the CHF enhancement. It was found that the CHF increases with the increase of subcooling and the simulation results agree with the Elkassabgi-Lienhard and Zuber correlations.