Numerical and experimental studies of gas–liquid flow and pressure drop in multiphase pump valves

A numerical and experimental study was carried out to investigate the two-phase flow fields of the typical three valves used in the multiphase pumps. Under the gas volume fraction conditions in the range of 0%–100%, the three-dimensional steady and dynamic two-phase flow characteristics, pressure drops, and their multipliers of the ball valve, cone valve, and disk valve were studied, respectively, using Eulerian–Eulerian approach and dynamic grid technique in ANSYS FLUENT. In addition, a valve test system was built to verify the simulated results by the particle image velocimetry and pressure test. The flow coefficient CQ (about 0.989) of the disk valve is greater than those of the other valves (about 0.864) under the steady flow with a high Reynolds number. The two-phase pressure drops of the three valves fluctuate in different forms with the vibration of the cores during the dynamic opening. The two-phase multipliers of the fully opened ball valve are consistent with the predicted values of the Morris model, while those of the cone valve and disk valve had the smallest differences with the predicted values of the Chisholm model. Through the comprehensive analysis of the flow performance, pressure drop, and dynamic stability of the three pump valves, the disk valve is found to be more suitable for the multiphase pumps due to its smaller axial space, resistance loss, and better flow capacity.

P806 Cavitation phenomenon in mechanical valves: not only microbubbles

Introduction It is well described the presence of microbubbles (MBs) which are high-velocity, small, bright echoes presences that occur with the closing/opening of the mechanical double disk valve, more frequently in mitral position but less frequent growth of the cavitation bubbles are described. We considered the echo studies of patients with growth of cavitation bubbles and we evaluate the possible impact of the hemodynamic parameters of their formation and then misdiagnosis with endocarditis. Methods We analyzed retrospectively the echocardiographic studies of 49 patients with growth of cavitation bubbles and we went back to all studies until the date of surgery if available, to see in how many of those echos, this phenomenon was present. Patient"s blood pressure (BP) and heart rate (HR) measurement were available for each echo study. For the present analysis the last echo study with or without growth of cavitation bubbles were considered. The last echo study without growth of cavitation bubbles was considered as control group. Results Fourty nine patients (M26/F23) with mean age of 46.5 ± 13.6 years were identify as having growth of the cavitation bubbles and a total of 325 echo studies were reviewed. All patients had mitral valve replacement but 4, that had only aortic mechanical valve. 43% had mitral-aortic valve replacement and 5 had 3 or 4 valves replaced. The follow-up period was of 3697 ± 2481 days, 52%±31% of the echo studies reviewed had growth of the cavitation bubbles. At the time of the study systolic BP was 124 ± 12.5 vs 121.1 ± 16.4 mmHg, p = 0.1 (echo study with versus without growth cavitation respectively), diastolic 72.7 ± 10.1 vs 69.4 ± 14.9 mmHg, p= 0.2; HR 81.3 ± 19.4 vs 73.7 ± 14.1 bpm, p = 0.05. No statistical differences in trans mitral gradients were found between the two groups (peak 11.8 ± 3.9 vs 11.7 ± 4.3 mmHg, p = 0.7; mean 4.6 ± 1.9 vs 4.2 ± 1 mmHg.6p = 0.1). 33 TEE were performed and in 50% of cases because of suspecion of endocarditis. Only 2 TEE were positive for endocarditis and one positive for pannus and high gradients across the valve in addition to cavitation. Conclusion Cavitation phenomenon in mechanical valves, in particular mitral bi-leaflet valve is well known but growth of cavitation bubbles is seldom described. We found that this fenomenon is frequently present although not constant, is related with increased HR and can be responsible of misdiagnosis with endocarditis. Abstract P806 Figure.