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

Abstract

ABSTRACTUnder 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.