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This paper aims to investigate the effect of three-dimensional (3D) inlet guide vanes (IGVs) on performance of a centrifugal pump.

A design method for 3D IGVs is proposed based on the controllable velocity moment, which is determined by a fourth-order dimensionless function. Numerical simulation of the centrifugal pump with IGVs is carried out by solving the Reynolds-averaged Navier–Stokes equations. The method of frozen rotor is applied to couple the stationary and rotational domain.

The efficiency of pump with 3D IGVs is higher than that with 2D IGVs for most prewhirl angles, which validate the advancement of 3D IGVs on prewhirl regulation. The effect of prewhirl regulation at small flow rate is more significant than that at large flow rate.

A prediction model of velocity moment based on the Oseen vortex is proposed to describe the flow pattern downstream the IGVs.

The purpose of this paper is to elucidate the detailed flow field and cavitation effect in the centrifugal pump volute at partial load condition.

Unsteady flows in a centrifugal pump volute at non-cavitation and cavitation conditions are investigated by using a computation fluid dynamics framework combining the re-normalization group k-e turbulence model and the mass transport cavitation model.

The flow field in pump volute is very complicated at part load condition with large pressure gradient and intensive vortex movement. Under cavitation conditions, the dominant frequency for most of the monitoring points in volute transit from the blade passing frequency to a lower frequency. Generally, the maximum amplitudes of pressure fluctuations in volute at serious cavitation condition is twice than that at non-cavitation condition because of the violent disturbances caused by cavitation shedding and explosion.

The detailed flow field and cavitation effect in the centrifugal pump volute at partial load condition are revealed and analysed.

The paper aims to investigate the clocking effect on a centrifugal pump with inlet guide vanes (IGVs).

The paper uses a computation fluid dynamics (CFD) framework to solve the unsteady flows in a centrifugal pump with inlet guide vanes. The relative position between the stationary vanes and the stationary volute tongue is defined as the clocking position when IGVs inside the suction pipe rotate along the circumferential direction.

The results show that clocking positions have little effect on the pump head and efficiency, however their influences are obvious for the pressure fluctuation and flow field in the centrifugal pump. The maximum difference of pressure amplitude at dominant frequency reach up to 28% on the monitoring point V8 at different clocking positions under design flow rate. For the large flow rate, the clocking effect on flow field and pressure fluctuation in centrifugal pump is similar to that of design flow rate. However, the clocking effect is nearly negligible at partial flow rate, because there are reverse flows around the tongue tip and obvious vortexes forming and developing in the impeller. Those complex phenomena interacting in the centrifugal pump make the clocking effect less evident.

The numerical investigation reveals the clocking effect on a centrifugal pump with inlet guide vanes, which also valuable for the stable operation and optimal design of centrifugal pumps.

Emergency situations call for effective means of providing quality education. Higher education institutions are therefore required to use effective and efficient online approaches for teaching and learning which necessitate students, academic practitioners and institutions to engage and interact with each other successfully. The purpose of this chapter is to discuss the importance of interaction and engagement in the use of blended learning online tools during emergency situations. The theoretical lens that informs the chapter is social constructivism which argues that learning is a social endeavour. The literature findings show that the effective engagement of students contributes to the overall quality of students’ produced experiences as well as pass rates. Furthermore, the importance of student–lecturer engagement and student–content engagement cannot be taken for granted. The right balance of synchronous and asynchronous online learning tools contributes to fruitful interaction and engagement. Online engagement seems to have many benefits as compared to conventional based engagement such as the ability of students to contribute to their teaching and learning. Despite these advantages, challenges associated with online learning such as balancing life commitments, confidence, students’ approach to learning, high investment costs in resources, motivation, competences of lecturers and students, interest of lecturers and students and efficacy of lecturers and students cannot be ignored. The authors therefore recommend that effective and efficient online learning requires the correct blend of online learning tools accompanied by the correct engagement strategies.

The recent COVID-19 pandemic underscores the need for educational innovation and digitalization during crises where many educational institutions were forced to shift to online and remote learning. This chapter is a discursive review of problems and solutions and key trends that have emerged because of crises. One of the key benefits of educational innovation and digitalization during crises is the ability to continue providing education and learning opportunities to students even when traditional face-to-face learning is not possible. Educational institutions need to invest in building resilient online learning ecosystems to ensure that education can continue uninterrupted even in the face of unforeseen disruptions. This ecosystem should include robust technological infrastructure, a diverse range of digital resources and tools, and training and support for educators. Ultimately, a resilient online learning ecosystem is not just a response to crises but a proactive investment in the future of education.

This study aims to assess the pitting resistance of austenitic stainless steel welded joints fusion zone (FZ) with high density of inclusions before and after surface treatment, including potentiostatic pulse technique (PPT) and pickling.

The potentiodynamic polarization tests and critical pitting temperature tests were carried out for estimating pitting resistance. The PPT and pickling were performed as surface treatment. Scanning electron microscope (SEM) and energy dispersive spectrometer were used for characterize the microstructure and elemental distribution. Electron back-scattered diffraction (EBSD) was used to assess the portion of phases and morphology of grains.

The weld metal exhibits a higher degree of alloying compared to the base metal, and it contains d-phase and sulfur-containing inclusions. Sulfur-containing inclusions serve as initiation sites for pitting, and they diminish the pitting resistance of weld metal. Both PPT and pickling can remove sulfur-containing inclusions, but PPT causes localized dissolution of the weld metal matrix around the inclusions, while pickling does not. Because of the high density of inclusions, certain pits initiated by PPT are significantly deeper, which makes the formation of stable pitting easier. Because of the high density of inclusions, certain pits initiated by the PPT are deeper. This characteristic facilitates the progression of these initial defects into fully developed, stable pits.

Analysis of pitting initiation in shielded metal arc welding FZ with PPT and ex situ SEM tracking observation. Explanation of why the PPT surface treatment is not able to enhance the pitting resistance of stainless steel with a high inclusion density.

The purpose of this study is to explore the transient characteristics of mixed-flow pumps during startup process.

This study uses a full-flow field transient calculation method of mixed-flow pump based on a closed-loop model.

The findings show the hydraulic losses and internal flow characteristics of the piping system during the start-up process.

Large computational cost.

Improve the accuracy of current numerical simulation results in transient process of mixed-flow pump.

Simplify the setting of boundary conditions in the transient calculation.

This paper aims to make it convenient for those who have only just begun their research into Community Question Answering (CQA) expert recommendation, and for those who are already concerned with this issue, to ease the extension of our understanding with future research.

In this paper, keywords such as “CQA”, “Social Question Answering”, “expert recommendation”, “question routing” and “expert finding” are used to search major digital libraries. The final sample includes a list of 83 relevant articles authored in academia as well as industry that have been published from January 1, 2008 to March 1, 2019.

This study proposes a comprehensive framework to categorize extant studies into three broad areas of CQA expert recommendation research: understanding profile modeling, recommendation approaches and recommendation system impacts.

This paper focuses on discussing and sorting out the key research issues from these three research genres. Finally, it was found that conflicting and contradictory research results and research gaps in the existing research, and then put forward the urgent research topics.

With an increasing number of Chinese private firms establishing primary level CPC Party committees, it is important to study the role of Party organizations in these firms. Using a nationwide survey of private firms in 2006, we empirically study the firm-level CCP committee's effect on workers' benefits and firm performance.

To overcome the potential endogeneity, we employ the regression discontinuity approach by utilizing the following rule from the Constitution of the CCP: Primary party committees should be established in any basic work unit with more than 3 full party members.

Our empirical results show that party committees in private firms have positive and statistically significant effects on many types of workers' benefits, including pension, unemployment insurance and workplace safety.

This paper highlights CCP committees as an important alternative mechanism in coordinating labor relationships in China when formal labor protecting institutions are weak.

The purpose of this study is to investigate the intergranular corrosion (IGC) susceptibility of a nitrogen-containing austenitic stainless steel QN2109. The intergranular corrosion (IGC) susceptibility of a nitrogen-containing austenitic stainless steel QN2109 was investigated.

The double-loop electrochemical potentiodynamic reactivation (DL-EPR) tests were carried out. Scanning electron microscopy and atomic force microscopy were used to characterize the microstructure.

The optimized test condition for QN2109 was 1 M H₂SO₄ + 0.01 M NH₄SCN at 40°C. The nose temperature of the temperature–time–sensitization (TTS) curve of QN2109 plot was approximately 750°C. Moreover, the IGC susceptibility started to appear at approximately 120 min. The Cr-depletion zone of QN2109 was generated by the formation of M23C6 rather than by the addition of nitrogen. The depth–width ratio of the grain boundaries after the DL-EPR tests decreased as the aging temperature increased. The degree of Cr depletion and size of the Cr-depletion zone at the grain boundary were reflected by the degree of sensitization and depth–width ratio, respectively.

The optimized test condition for DL-EPR tests of a nitrogen-containing austenitic stainless steel QN2109 was investigated. The TTS curve of QN2109 was first plotted to avoid IGC failure. The morphology of the Cr-depletion zone was reflected by the depth–width ratio.