Power transient critical heat flux in a narrow rectangular channel under downward flow

Abstract

Power transient critical heat flux (CHF) experiments were conducted under downward flow conditions in a narrow rectangular channel simulating a sub-channel consisting of plate-type fuels for a research reactor. The test section is designed as a sub-channel with a wetted width of 66.6 mm, heated width of 62 mm, gap size of 2.35 mm, and length of 640 mm. In the experiment, a mass flux of 3750 kg/m2s with a downward flow, an inlet temperature of 37 °C, and outlet pressure of 170 kPa were maintained constantly at a given heat flux transient condition. The heat flux was exponentially increased with the power increase rate ranging from 0.03 to 1 s−1 for the simulation of power transients in the reactivity-initiated accidents of the research reactor. It was found that the CHF increased significantly as the power increase rate increased at a given flow condition. The power transient CHF was analyzed using a dimensionless velocity consisting of parameters representing the liquid-sublayer thinning mechanism that is expected in the vicinity of the heated wall. Finally, we developed a power transient CHF correlation based on the experimental data set consisting of the present data, data of Kataoka et al., and the R-12 data of Celata et al. The developed correlations showed an average error of 0.24% and root mean square error of 3.09% against the experimental data set for power increase rates of 0.03–1 s−1.