TWO-PHASE FLOW INSTABILITY IN PARALLEL CHANNELS
Experiments have been conducted on two-phase flow instability in parallel channels under forced and natural circulation, using water. Two types of flow oscillation were observed; one occurs at nearly zero steam quality (Type I), the other at relatively high steam quality (Type II). The analyses done show that gravitational pressure drop is the governing factor in Type I oscillation, and frictional pressure drop is dominant in Type II oscillation. Type I oscillation had sometimes been regarded as "pressure drop oscillation" caused by negative slope on the flow rate vs. pressure drop curve. However, it is found that this kind of static analysis is inadequate, because it provides only a partial explanation compared with that obtained by dynamic analysis. Here it is shown that the "pressure drop oscillation" is included in Type I oscillation induced by the feed back effect between flow rate and gravitational pressure drop.