Effect of the Inlet Gas Void Fraction on the Work Performance of the Multiphase Pump at Different Cavitation Stages

The inlet gas void fraction (IGVF) has a great effect on the power performance of the multiphase pump, and the effect is even greater under the cavitation condition. To reveal the effect of the IGVF on the cavitation evolution and the work performance of the multiphase pump at different cavitation stages, the cavitation flow was calculated numerically for the pump under different inlet gas void fractions (IGVFs) of 0%, 10% and 20%. Meanwhile, the numerical simulation method was verified experimentally. The results showed that the increase of the IGVF could improve the cavitation performance of the multiphase pump and inhibit the increasing rate of the vapor. With the aggravation of the cavitation, the output power of the impeller decreased gradually under different IGVFs. In addition, the variation trend of the output power and the net energy gained by the fluid within each domain were exactly the same. At the same time, the position of better work performance was located in the impeller fore area at the critical and serious cavitation stages, while when the cavitation developed to the fracture cavitation, the position of better work performance moved to the impeller back area. At the fracture cavitation stage, the main work region of the multiphase pump moved from the back area to the fore area of the impeller with the increase of the IGVF. The research results are of great significance in improving the performance of the multiphase pump.

Experimental Study on Two Different Gas-Liquid Separators Under Different Flow Patterns

Gas-liquid separation is widely used in many fields, such as nuclear energy and petroleum resources. And the gas-liquid mixture separated gradually shows the characteristic of wide range of gas void fraction and variable flow patterns. However, the current separators only suit for narrow range of gas void fraction or single flow patterns. In this research, two different new type separators using centrifugal technology were designed and an experimental system was constructed to test the two separators using dry air and water under different flow patterns, including bubble, slug and churn flow. One was called inline separator consisting of three swirls and another was called double-layer cylinder separator composed of a central tube, a swirl and an outer tube. The results show that the separation performance of the inline separator was sensitive to flow patterns and the two-layer cylinder separator keeps high efficiency in different flow patterns. In bubble flow and slug flow patterns, the two separators kept high efficiency, while the oscillation of the gas core in the inline separator aggravated under slug flow condition. When increasing the gas void fraction, the turbulence of the churn flow led to the diameter of the gas core change drastically and reduce separation efficiency significantly.

Gas Void Fraction Measurement of Gas-Liquid Two-Phase CO2 Flow Using Laser Attenuation Technique

The carbon capture and storage (CCS) system has the potential to reduce CO2 emissions from traditional energy industries. In order to monitor and control the CCS process, it is essential to achieve an accurate measurement of the gas void fraction in a two-phase CO2 flow in transportation pipelines. This paper presents a novel instrumentation system based on the laser attenuation technique for the gas void fraction measurement of the two-phase CO2 flow. The system includes an infrared laser source and a photodiode sensor array. Experiments were conducted on the horizontal and vertical test sections. Two Coriolis mass flowmeters are respectively installed on the single-phase pipelines to obtain the reference gas void fraction. The experimental results obtained show that the proposed method is effective. In the horizontal test section, the relative errors of the stratified flow are within ±8.3%, while those of the bubble flow are within ±10.6%. In the vertical test section, the proposed method performs slightly less well, with relative errors under ±12.2%. The obtained results show that the measurement system is capable of providing an accurate measurement of the gas void fraction of the two-phase CO2 flow and a useful reference for other industrial applications.

Numerical simulation of gas–liquid flow behavior in the nozzle exit region of an effervescent atomizer

The pressure drop and particular geometric structure of the nozzle exit region of an effervescent atomizer cause complex changes in the flow pattern, which could affect the spray performance. In this study, the gas–liquid two-phase flow behavior in the nozzle exit region of the effervescent atomizer was investigated numerically. The results show that the flow behaviors in the nozzle exit region have disparate characteristics with different upstream flow regimes. For upstream churn flow, the liquid film morphology is closely related to fluctuation in the gas–liquid velocity, and the flow parameters (fluids’ velocities and gas void fraction) at the exit section vary regularly with time. For upstream bubbly flow, the instantaneous gas void fraction is determined by the bubble distribution inside the mixing chamber. The bubble will form a tadpole-like shape as a result of the complex flow field and the surface tension. The flow parameters at the exit section are in an oscillatory decay, and the fluctuation amplitude is larger than for churn flow. For upstream slug flow, the gas void fraction varies significantly with time. The discrete characteristic of the gas–liquid flow parameters at exit section is very obvious.

Research on Stagger Coupling Mode of Pulse Duration and Tool Vibration in Electrochemical Machining

Tuning the coupling of pulse duration and tool vibration in electrochemical machining (PVECM) is an effective method to improve machining accuracy and surface quality. In general, the pulse is set at the same frequency as the tool vibration, and a symmetrical distribution is attained at the minimum inter-electrode gap. To analyse the characteristics of the electrolyte fluid flow and of the electrolysis products in the oscillating inter-electrode gap, a dynamic simulation of the PVECM process was carried out. The simulation results indicated that the electrolyte pressure and gas void fraction when the pulse arrived as the inter-electrode gap was narrowing clearly differed from those when the inter-electrode gap was expanding. Therefore, in addition to the traditional symmetry coupling mode, two other coupling modes called the pre-position and the post-position coupling modes are proposed which use a pulse either just before or just after the minimum inter-electrode gap. Comparative experiments involving the feed rate and machining localization were carried out to evaluate the influence of the three coupling modes. In addition, current waveforms were recorded to analyse the differences between the three coupling modes. The results revealed that the highest feed rate and the best machining localization were achieved by using the pre-position coupling mode.