A Study on the Hydrodynamic Instability in Boiling Channels : 1st Report, The Instability in a Single Boiling Channel

Abstract

An investigation is carried out on the hydrodynamic instability which has been observed in two-phase flow systems, such as boiling water reactors and once-through boilers. In this paper a system having a single boiling channel is treated. The equation of oscillation for the circulation flow rate is derived from the laws of conservation of mass, energy and momentum. The damping coefficient in this equation is given as the inclination of the characteristic curve which represents the relation between pressure losses and circulation flow rate. As the result, it is found that, when the equilibrium of the hydrodynamic system lies in the range of negative inclination of the characteristic curve, the system is unstable and a hydrodynamic oscillation is generated. In the case of forced circulation, the system is expected to be more stable than the natural circulation system, owing to the positive damping caused by the pump included in the circuit.