Experimental investigation of two-phase flow pressure-drop type instabilities in parallel vertical internally ribbed pipes at low mass flow rate

The research covers the experimental investigation of two-phase flow instabilities in parallel vertical internally ribbed pipes at low mass flow rate in the high-pressure steam-water test loop. The tested tube is an outlet diameter of 28.6mm and a wall thinkness of 5.8mm. The pressure-drop type oscillations are found in the experiments. The effects of pressure, mass flow rate and inlet subcooling on instabilities are studied. The results show that the boundary heat flux of pressure-drop type oscillations increase with increase of inlet pressure, mass flow rate and inlet subcooling. It is found that sysetem pressure, inlet subcooling and mass flow rate have great effects on amplitudes and periods of two-phase flow instabilities. In addition, it is found that the effects of pressure on periods of pressure-drop type oscillations represent two different trends in the test. When pressure is lower then 4Mpa, the periods of pressure-drop type oscillation increase with pressure increasing, but when pressure is higher then 4Mpa, the oscillation periods decrease with pressure increasing.