Effect of outlet impeller diameter on performance prediction of centrifugal pump under single-phase and cavitation flow conditions

In this current study, the transient numerical calculations using CFD code are carried out under different outlet impeller diameters for the flow field within a centrifugal pump under single-phase and cavitation conditions. Both qualitative and quantitative analyses are carried out on all of these results in order to better understand the flow structure within a centrifugal pump. Also, the investigations using different outlet impeller diameters configurations relating to the static pressure, velocity magnitude, vapour volume fraction variations, as well as pressure fluctuations in both time and frequency domain at the impeller and volute of the pump are analysed. Velocity and static pressure variations of the pump under different outlet impeller diameters range (200, 210 and 220 mm) are investigated. Reliable model is developed and validated, at various pump operating conditions, to analyse the characteristics of pressure fluctuations in both time and frequency domain. Cavitation occurrence, under different outlet impeller diameters and flow rates, are detected and correlated, using a CFD model (volume fraction distributions). Based on the developed model’s findings, at the set operating conditions ranges, the distribution and impact (cavitation and head-wises) of both the pressure and velocity are analysed. The average pressure fluctuation in the volute for do = 210 mm is higher than for do = 200 mm by about 6.74%, also the maximum pressure fluctuation for do = 220 mm is higher than for do = 210 mm by around 7.4%. Furthermore, the maximum pressure fluctuation in the impeller for do = 210 mm is higher than for do = 200 mm by 12.48%, also for do = 220 mm is higher than for do = 210 mm by 10.8%. The developed CFD models are proved valuable tools in identifying and optimizing the pump performance and characterization. The head for when do = 220 mm is higher than for when do = 200 mm under both single-phase and cavitation conditions by around 14.13% and 14.69%. The maximum pressure fluctuation for do = 200 mm is lower than for do = 210 mm by 41.58%. Furthermore, the maximum pressure fluctuation at the impeller for do = 220 mm is higher than the two models. There is a small clearance between the impeller and the volute for this model, leading to the pressure fluctuation amplitudes being higher than the other above models.

Severe Intraocular Pressure Fluctuation following Hemodialysis after Cataract Surgery in a Patient with Chronic Renal Failure

Purpose: To report a case of severe intraocular pressure fluctuation following hemodialysis after cataract surgery in a patient with chronic renal failure.Case summary: A 51-year-old female patient on hemodialysis for chronic renal failure, who was seen regularly by our retina clinic for proliferative diabetic retinopathy and right eye cataract, presented with decreased visual acuity in her right eye. During phacoemulsification under the diagnosis of right eye cataract, zonular dialysis and posterior capsule rupture occurred and intraocular lens ciliary sulcus insertion was performed. Following hemodialysis 3 days after the surgery, the patient complained of headache and right eye pain. The intraocular pressure of the right eye had increased to 44 mmHg. Mild inflammation in the anterior chamber was found with remnant lens material present at the inferior anterior angle. The use of glaucoma eye drops, anterior chamber paracentesis, and anterior chamber irrigation reduced the intraocular pressure and improved the patient’s symptoms. However, a severe increase in intraocular pressure recurred with the above symptoms, again following hemodialysis. Intraocular pressure fluctuation was repetitively present after serial hemodialysis treatments for 1 month, at which point cataract and glaucoma surgeries were considered. However, the intraocular pressure stabilized afterwards; thus, the patient remained under observation and was treated with glaucoma eye drops.Conclusions: Inflammation and a decrease in the aqueous outflow facility due to remnant lens material and the use of an ophthalmic viscoelastic device in cataract surgery may cause severe intraocular pressure fluctuations in patients undergoing hemodialysis for chronic renal failure.

Analysis of the Influence of Inlet Guide Vanes on the Performance of Shaft Tubular Pumps

To study the influence of inlet guide vanes (IGVs) on the pressure pulsation of a shaft tubular pump, this paper first conducts an experiment to study IGVs. Then, numerical calculations of the shaft tubular pump with and without IGVs are performed to analyze the hydraulic performance and pressure fluctuation characteristics. Finally, the reliability and accuracy of the data are verified by a model test. Numerical simulation results show that with additional IGVs, the pressure pulsation amplitude at the impeller inlet first decreases and then increases under small-flow and design conditions but gradually increases under large-flow conditions. When the IGVs are added to the impeller inlet of the shaft tubular pump, the hydraulic loss in front of the impeller inlet increases, resulting in a significant drop in the head and efficiency of the pump device when the flow rate is less than 1.12 Qd; when the flow rate is greater than 1.12Qd, the head and efficiency of the pump device do not change significantly. IGVs can improve the condition of impeller water inflow and reduce pressure fluctuation on the blade surface.

Effects of the Rates on the Performance and Pressure Pulsations of a High-Speed Pump with Straight Blade

Along with the crucial requirement for efficiency improvement in the cutting-edge petrochemical technology, the evaluation of the dynamic performance characteristics of high-speed pump is becoming increasingly important. It has become a main topic in the research of high-speed pump to minimize the pressure pulsation induced by the fluid in the pump body, so as to reduce the mechanical vibration. Although the research on the transient flow characteristic and pressure fluctuation of a high-speed pump with straight blades is of great significance, it has been seldom explored. In this work, the flow instability of a 16 straight-blade high-speed centrifugal pump is studied numerically at a rotational speed of 8500 rpm and flow rate of 3 m3/h. Results show that with the influence of rotor-stator interaction, time-domain pressure signals at the tongue show double peak characteristic, whereas a single peak characteristic exists at the diffuser wall. The pressure fluctuation near the tongue is reduced to approximately half of that at the volute wall by the water ring effect accompanied with the high-pressure factor. At the tongue region, the amplitude of the blade passing frequency is reduced by the unsteady flow, whereas the harmonic wave was increased at 2–4 times of the blade passing frequency.

Pressure fluctuation on casing wall and investigation to tip leakage flow of contra-rotating small hydro-turbine

Renewable energy is strongly recommended to replace the traditional fossil fuels to solve the severe environmental pollution. However, small hydro-turbine performs lower efficiency, and it is also easy to be blocked and impacted. Therefore, the contra-rotating rotors are adopted to overcome the disadvantages of small hydro-turbine. The performance and internal flow condition of contra-rotating small hydro-turbine have been clarified. In this paper, a new transparent casing is manufactured, and pressure fluctuation experiments are conducted. The pressure fluctuation experiments are to clarify the pressure fluctuation during the running of contra-rotating small hydro-turbine. Then the hydraulic stability of contra-rotating small hydro-turbine can be further investigated. According to the experiment results, for the new model, most of the amplitudes of pressure fluctuation are decreased. The maximum decreasing percentage of peak-to-peak value is 74.22%, and it is appeared on the point of Pr3. On frequency domain, the dominant frequencies of pressure fluctuation are rotation frequency and blade passing frequency. The investigation to tip leakage flow of contra-rotating small hydro-turbine is conducted based on the pressure fluctuation experiment and numerical simulation. The tip leakage vortex is identified by Q-criterion. The pressure distributions in tip clearance area show that the tip leakage vortex of new model is suppressed, and this helps to reduce the amplitude of pressure fluctuation in tip clearance area.