Flow excursion phenomenon and its mechanism in natural circulation

An experiment was performed on the test loop (HRTL-5), which simulates the geometry and system design of a 5-MW nuclear heating reactor. In a wide ran ge of inlet subcoolings, different flow modes, such as single-phase stable flow, subcooled boiling stable flow, subcooled boiling static flow excursio n, density-wave oscillation and stable two-phase flow in the natural circul ation system have been described. The phenomenon and mechanism of the stati c flow-excursion, which has never been studied well on this field, is espec ially interpreted. The experimental results show that, in the process of fl ow excursion, the mass flow rate and the inlet temperature decreases, while the exit temperature increases smoothly. As the process of the excursion c ontinues for about 1 h, short period dynamic flow oscillation occurs, which can only be seen in the process of this static flow excursion, and has als o never been studied well. These static and dynamic flow instabilities comb ine together and continue for about 2 h, then a point is reached, at which the static flow excursion disappears, but the dynamic flow oscillation cont inues. The mechanism of the static flow excursion is interpreted through tw o sets of curves for flow resistance pressure drop and driven head in natur al circulation, and one curve for the natural circulation operation under s pecial thermohydraulic condition. The study of the how excursion and its co ncerned dynamic flow oscillation is of great significance for the developme nt of the nuclear heating reactor under natural circulation. (C) 2000 Elsev ier Science S.A. All rights reserved.