Numerical investigation of departure from nucleate boiling for subcooled flow boiling in a rolling tube

A crucial issue in floating nuclear plants is the critical heat flux (CHF) under oscillatory conditions by ocean waves. CHF must be predicted considering the dynamic motion of the floating platform. We present numerical simulations for predicting the DNB (departure-from-nucleate-boiling)-type CHF of subcooled R134a flow in a rolling tube and provide physical insight into the dynamic flow behavior regarding the DNB, considering rolling amplitudes of 15 degrees, 30 degrees, and 40 degrees and a rolling period of 6 s. The local wall temperature and void fraction depended mainly on the dynamic changes in the gravitational direction. Gravity had the effect of lowering DNB. The Euler force created a secondary liquid flow that somewhat reduced the liquid temperature at the heating wall during the rolling period, thereby enhancing the convective and quenching heat fluxes. Furthermore, the secondary flow rapidly increased the liquid area fraction at the overheated wall and decreased the temporarily increased wall temperature before DNB occurred. The secondary flow had the effect of increasing DNB. In this study, the effect of increasing the DNB value is greater than the effect of reducing the DNB value. The occurrence of DNB depended on sufficient cooling of the downward-facing wall during the rolling period.