Experimental investigation on saturated pool boiling CHF for downward facing heating surface with different sizes and aspect ratio

IVR-ERVC (In-Vessel Retention – External Reactor Vessel Cooling) is a key severe accident management for keeping the integrity of the reactor pressure vessel (RPV) lower head. One of most important topics is the characteristics of the CHF (Critical Heat Flux) on the outside wall of RPV lower head. Some experiments had been conducted to investigate the effect of the orientation on characteristics of the boiling heat transfer and CHF for downward facing heating plate. While the size of the heating plate used may have an appreciable effect on the characteristics of the CHF. In this work, experiments were carried out to investigate the effects of the heater surface area and length-width ratios on saturated pool boiling and CHF for downward facing heating surface. Experimental results indicated that the inclined angle has little effect on the saturated pool boiling heat transfer, and the wall superheat of triggering of CHF was greater for the larger inclined angle. For the same aspect ratio of the heating surface, the CHF decreased with the increase of the heating surface area for the same surface orientation. It also indicated that the CHF was influenced by the bubble escaping length and wetted perimeter complicatedly, and the short edge effect had an appreciable influence on CHF based on present experimental work. Meanwhile, a modified El-Genk and Guo CHF correlation was proposed based on CHF data with the same aspect ratio of the heating surface, which could consider the effect of heating surface area on pool boiling CHF.