A study on the measurements to prvent flow oscillations in a heated channel

The stability of the two-phase flow in a heated channel is very important in the design and operation of the industrial boilers, chemical reactors, and light water nuclear reactors, because it can cause flow oscillations and lead to a violation of thermal limits with resultant overheating of the channels and cladding. This study presents a systematic analysis to the channel entrance and exit orifice of dimensionless parameters in a homogeneous equilibrium model. The stability effects of inlet and outlet orifice is examined on the base of static charateristic curves. Then the complicated transfer funtion of flow dynamics of a heated channel with inlet and outlet orifice which gives consideration to the transportation lag of density wave is derived, and examined by applying Nyquist stability criterion in control engineering. The results are summed up as follows; 1. Entrance orifice stabilizes the flow oscillations in static and dynamic chartacteristics. 2. Exit orifice enhances the flow fluctuations in both characteristics. 3. Horizontal channel is more stable than upright channel in dynamic characteristics, which the former becomes more unstable than the latter in static characteristics. To prevent the flow oscillation, the orifice installation at channel is highly recommendable, but exit orifice is undesirable because it destabilizes the two-phase flow in a channel. (Author)