Two-phase flow instability in a liquid nitrogen heat exchanger

Experimental results on the two-phase flow instability in a liquid nitrogen heat exchanger are shown. The experiments are carried out in four cases with various combinations of tube lengths with some bends, the attitude of the heat exchanger, the secondary fluid and the subcooler. A stability map and periods of oscillations are obtained in each experiment. In the case of a vertical heat exchanger with a 6 m pipe containing four bends, there are two unstable regions ; while there is one unstable region in the case of that with two bends. In the experiment using the horizontal heat exchanger with four bends and steam as the secondary fluid, oscillations of higher modes together with the fundamental one occurred. For the example of the same heat exchanger with a subcooler, oscillations of two modes occurred. A computer code is developed based on the linear analysis technique with the density wave oscillation model. With this code, experimental data are analyzed and it is found that the oscillations in these experiments are those of the density wave type. (author)