Abstract
In order to justify the theoretical analysis on the hydrodynamic instability in boiling channels presented in previous papers, experiments are conducted using the systems with a single boiling channel, two parallel boiling channels and ten parallel boiling channels. The following facts which have been predicted theoretically are recognized experimentally. (1) The hydrodynamic instability in boiling channels is caused by the negative resistance due to the characteristic curves of pressure loss. Then, if subcooling becomes smaller, the system becomes stable. Exit void fraction has no direct influences on stability. There can be the case where the system becomes stable, when heat input is increased. The hydrodynamic oscillation can be generated also in the system without a riser. (2) Though, in a single boiling channel, a throttle in the downcomer gives damping effects to the system, the out-of-phase modes of vibration between channels can remain in parallel boiling channels, even when a throttle is included in the downcomer. Reverse flow can be generated in the system with parallel boiling channels. (3) As the number of boiling channels becomes larger, the in-phase-mode of vibration, in which all channels vibrate in the same phase, is more difficult to generate, and the mutual vibrations between the channels are predominant. (4) As the number of boiling channels becomes larger, there exist more equilibriums corresponding to reverse flow, then a reverse flow is generated more frequently in a multi-channel-system. In a multi-channel-system, there exist several channels which are settled in reverse flow.
