The working capability of multi-stage pumps, such as electrical submersible pumps (ESPs) handling multiphase flow, has always been a big challenge for petroleum industries. The major problem is associated with the agglomeration of gas bubbles inside ESP-impellers, causing pump performance degradation ranging from mild to severe deterioration (surging/gas pockets). Previous literature showed that the two-phase performance of ESPs is greatly affected by gas involvement, rotational speed, bubble size, and fluid viscosity. Thus, it is necessary to understand which parameter is actually accountable for performance degradation and different flow patterns in ESP, and how it can be controlled. The present study is mainly focused on (1) the main parameters that impede two-phase performance of different ESPs; (2) comparison of existing empirical models (established for two-phase performance prediction and surging initiation) with our single-stage centrifugal pump results to determine their validity and working-range; (3) gas-handling techniques applied to enhance the multiphase performance of ESPs. Firstly, it aims at understanding the internal flow mechanism in different ESP designs, followed by test studies based on empirical models, visualization techniques, bubble-size measurements, and viscosity analysis. The CFD-based (computational fluid dynamics) numerical analysis concerning multiphase flow is described as well. Furthermore, gas-handling design methods are discussed that are helpful in developing the petroleum industry by enhancing the multiphase performance of ESPs.

In the light of the significance of the rotating machinery and the possible severe losses resulted from its unexpected defects, it is vital and meaningful to exploit the effective and feasible diagnostic methods of its faults. Among them, the emphasis of the analysis approaches for fault type and severity is on the extraction of useful components in the fault features. On account of the common cyclostationarity of vibration signal under faulty states, fault diagnosis methods based on cyclostationary analysis play an essential role in the rotatory machine. Based on it, the fundamental definition and classification of cyclostationarity are introduced briefly. The mathematical principles of the essential cyclic spectral analysis are outlined. The significant applications of cyclostationary theory are highlighted in the fault diagnosis of the main rotating machinery, involving bearing, gear, and pump. Finally, the widely-used methods on the basis of cyclostationary theory are concluded, and the potential research directions are prospected.

Photocatalytic hydrogen evolution plays a critical role in the exploration of the clean and sustainable energy. Owing to its special structure and features, two-dimensional (2D) graphitic carbon nitride (g-C3N4) has attracted tremendous attention. However, some deficiencies of pristine g-C(3)N(4 )inhibit its photocatalytic application, particularly the low quantum efficiency of hydrogen evolution. Therefore, it is valuable to develop 2D new composites based on g-C3N4 so that the synergistic effects of the two original materials can be achieved. This article attempts to summarize the modification strategies of 2D g-C3N4-based composites, including the construction of heterojunctions, morphology control, doping method, surface modification and co-catalyst loading. The application and progress in photocatalytic hydrogen evolution are also highlighted. The limitations are taken into account to provide further information for the improvement in the quantum efficiency of hydrogen by 2D g-C3N4-based composites. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

This study basically summarizes the recent developments of the flow-induced noises in a centrifugal pump. Especially, the different numerical and experimental methods that have been used to analyze the internal flow properties and its effect on the generation of flow-induced noise. Firstly, it focuses on the physical mechanism behind the internal flow features and gives a complete description of the complex flow and its instabilities. The flow behavior is demonstrated with the help of velocity triangle diagram and Euler equation. The use of PIV is significant in experimental research to examine the internal flow fluctuations. However experimental methods are not sufficient because the flow within centrifugal pump is three-dimensional and turbulent due to its complex geometry. Therefore, the fluctuating behavior of the fluid within pump has been analyzed by computational fluid dynamics (CFD) and it gained great advancements. Secondly, the different types of noise sources in centrifugal pumps are summed. These sources are also described according to the noises coming from different mechanisms such as the effect of rotor-stator interaction, cavitation, pressure pulsations and turbulence. Further, the research methods that had been used to measure and reduce the effect of these noise sources on centrifugal pumps are described in two aspects: Numerical simulation method based on CFD/CA and experimental analysis. The present paper draws the conclusion that the interaction between volute-tongue and impeller blade is the primary factor that produces noise in centrifugal pumps. Likewise, the blade passing frequency, generated by the interaction between impeller and volute-tongue, is the dominant frequency and the main source for the production of noise. A significant reduction in noise can be obtained by optimizing these factors.

This study basically summarizes the recent developments of the flow-induced noises in a centrifugal pump. Especially, the different numerical and experimental methods that have been used to analyze the internal flow properties and its effect on the generation of flow-induced noise. Firstly, it focuses on the physical mechanism behind the internal flow features and gives a complete description of the complex flow and its instabilities. The flow behavior is demonstrated with the help of velocity triangle diagram and Euler equation. The use of PIV is significant in experimental research to examine the internal flow fluctuations. However experimental methods are not sufficient because the flow within centrifugal pump is three-dimensional and turbulent due to its complex geometry. Therefore, the fluctuating behavior of the fluid within pump has been analyzed by computational fluid dynamics (CFD) and it gained great advancements. Secondly, the different types of noise sources in centrifugal pumps are summed. These sources are also described according to the noises coming from different mechanisms such as the effect of rotor-stator interaction, cavitation, pressure pulsations and turbulence. Further, the research methods that had been used to measure and reduce the effect of these noise sources on centrifugal pumps are described in two aspects: Numerical simulation method based on CFD/CA and experimental analysis. The present paper draws the conclusion that the interaction between volute-tongue and impeller blade is the primary factor that produces noise in centrifugal pumps. Likewise, the blade passing frequency, generated by the interaction between impeller and volute-tongue, is the dominant frequency and the main source for the production of noise. A significant reduction in noise can be obtained by optimizing these factors.