Research on pressure-drop type instabilities between different parallel vertical rifled tubes at lower mass velocity

An experimental study was carried out on the pressure-drop type instabilities of the two-phase flow of the parallel vertical rifled tube in the high-pressure vapor-water test loop. The comparison of the effects of two types of tubes on the two-phase flow instabilities have been conducted. The results show that with the increase of inlet pressure and mass flow rate, the boundary heat flux of pressure-drop type oscillations increases; the boundary dryness thresholds of pressure-drop type oscillations increase with the increase of inlet pressure, In addition, with the increase of mass flow rat, the boundary dryness thresholds of pressure-drop type oscillations are increased with rifled tube of Φ31.8 mm x 6 mm, but first increased and then decreased for the rifled tube of Φ28.6 mm x 5.8 mm. It is also found that the range of the boundary dryness thresholds and the periods of the oscillations of pressure-drop type oscillations for two types of tubes are similar. Under the same operation parameters, the rifled tube of Φ31.8 mm x 6 mm is more stable. (authors)