Critical heat flux in various inclined rectangular straight surface channels

One-dimensional experiments with three kinds of copper blocks were performed for an investigation of critical heat flux (CHF) to account for a ratio of heated length to gap size and twist angle as well as gap size and surface inclination angle ranging from the vertical (90°) to fully downward facing (180°) position effects in the rectangular channel. The CHF can be decreased if it is not easy for the bubble to escape from the heated surface. All parameters affecting the CHF (e.g., gap size, surface inclination angle, heated length to gap size ratio, and twist angle) affect the bubble escaping from the heated surface. Transition angles were spotted at which the CHF changes with a rapid slope, as the inclination angle is increased, which is consistent with the existing literature. A semi-empirical CHF correlation was developed for inclined narrow rectangular channels through a dimensional analysis. The correlation reflected from the best-estimate CHF values can be provided for realistically assessing the thermal margin to a failure of the lower head during a severe accident involving a relocation of the molten core material in a reactor vessel.