Experimental study of two-phase flow instability of vertical parallel rifled tube with different sizes at low-mass flow rate

Under certain operating conditions, two-phase flow oscillations can occur and induce undesired problems such as system control, vibration, tube burn-out, etc. Therefore, it is essential to avoid and control two-phase flow instabilities when designing and operating equipments that are susceptible to such effects. The authors conducted an experimental study of vapor-liquid two-phase flow instabilities in vertical parallel tubes for a high-pressure vapor-water loop. Two types of vertical parallel rifled tubes (31.8 mm OD × 6 mm thickness, and 28.6 mm × 5.8 mm) were used as the tube sections. During experimentation, pressure-drop and density-wave type oscillations appeared, and the influence of the inlet pressure, mass flow rate, and inlet subcooling on the two-phase flow instability in both types of vertical parallel-connected tubes was studied. The results showed that with an increase in the inlet pressure and mass flow rate, the boundary thermal load of the pressure-drop and density-wave oscillations increased. As the inlet pressure increased, so the boundary quality of the pressure-drop and density-wave oscillations occurring in both types of the rifled tubes also increased. Experiments showed that under the same operating conditions, the stability of the 31.8 × 6 mm rifled tube is better than the 28.6 × 5.8 mm rifled tube. For the 31.8 × 6 mm rifled tube, the occurrence of the boundary quality of the pressure-drop type oscillation increased with the increasing mass flow rate. However, for the 28.6 × 5.8 mm rifled tube, the occurrence of the boundary quality of the pressure-drop oscillation first increased and then decreased with an increasing mass flow. © 2011 Curtin University of Technology and John Wiley & Sons, Ltd.