The Modes of Flow Oscillation in Multi-Channel Two-Phase Flow Systems

In this paper, some results of the experimental investigations on oscillation modes of multi-channel two-phase flow systems are reported. In the first part, phase relation between oscillating channels is studied using a Freon-113 test rig; the number of parallel channels is varied up to five. It is found that, if the thermohydraulic characteristics of all channels are identical, they oscillate with the same amplitude and equally out of phase with each other, and that if the characteristics are not identical various modes become possible. In the second part, interaction between oscillating channels is studied in detail at a two-channel air-water test rig. In this rig, it is indispensable to equip every air and water supply lines with compressible capacities in order to realize flow oscillation, and only the oscillations originated from Ledinegg instability, i.e. some kinds of pressure drop oscillation, can be observed. Effects of the compressible capacities and the hydraulic states of the channels on the modes of oscillation are examined. Other than the types of oscillation observed in single channel systems, one inherent to multi-channel systems is observed which is named as modulation wave one. It is clear that this stems from channel interaction.