Dynamic instabilities in tubes of a large capacity, straight-tube, once-through sodium heated steam generator

Abstract

Density-wave type dynamic instabilities were detected in the tubes of a large-capacity sodium heated steam generator. The peak-to-peak amplitudes of these oscillations varied between 9 and 60 K and the periods between 4 and 7.6 s. Our experimental data for the periods and the inception conditions of the dynamic instabilities, and the data found in literature obtained for a tube and a rectangular channel across which pressure drop is constant, have been correlated with simple equations for the following range of conditions: pressure: 4.1–17 MN/m 2; exit quality: 0.27–1.59; inlet subcooling: 3–111K; ratio of heated length to hydraulic diameter: 153–1921; hydraulic diameter: 0.0045–0.0126 m; enthalpy rise in the channel: 582–2130kJ/kg; mass velocity: 353–2088 kg/m 2s; average heat flux 0.1–3.25 MW/m 2; period: 0.35–7.6 s. At the start of dynamic instabilities the steam quality (or the enthalpy of the steam or steam/water mixture) at the outlet of a boiling channel is constant for a given subcooling, pressure and geometry in the low-subcooling range, and for a given pressure and geometry for the range of medium and high subcoolings. The period of the dynamic instabilities is a function of the transit time of a fluid particle in the boiling region of a channel, the Froude number and the ratio of the length of the boiling region to the total heated length. A hot channel factor has also been established, which relates the operating conditions in the tube in which the dynamic instabilities occur first, to the average operating conditions in the steam generator.