Reflux condensation and transition to natural circulation in a vertical U tube

Reflux and natural circulation condensation in vertical inverted U-tube steam generators form an important heat removal mechanism for nuclear reactors in certain accidents. Conensation was studied in a single vertical tube with a cooling jacket. The behavior of the system used was explained by postulating that ''flooding''conditions were reached at the inlet when the pressure difference became large enough for the liquid column to form above the condensing region. A small perturbation analysis of the stability of the condensing and liquid column regions was done using a lumped parameter approach and constant pressure boundary conditions. Experimental results on the frequency of oscillations in a single tube followed the qualitative trends predicted by the linear analysis, but the predicted frequencies were about twice as high as those observed. 2 refs