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关键词： Rotors   Induction motors   Monitoring   Vibrations   Amplitude modulation   Bars   Stator windings   Airgap flux   eccentricity   fault diagnostics   leakage flux   load unbalance   misalignment   search coil   spectral analysis   squirrel cage induction motor   vibration  

摘要： Motor current signature analysis (MCSA) has been accepted in the field as a reliable means of detecting faults in the rotor cage of induction motors. However, there are many limitations to MCSA-based detection for other types of faults including rotor eccentricity and load defects. Recently, there has been increasing interest in airgap or leakage flux monitoring as an alternative to replace or complement MCSA. Flux monitoring can provide a reliable means of detecting rotor faults since anomalies in the rotor magnetomotive force or airgap can be directly observed. In this article, a new method based on monitoring the attenuation of rotor rotational frequency sidebands in the flux spectra is proposed for reliable detection and classification of rotor cage and eccentricity faults. It is also shown that flux monitoring can provide detection of rotor faults that is insensitive to the load defects. An experimental study under controlled broken bar, eccentricity, misalignment, and load unbalance conditions are given to support the claims. The results show that rotor cage, eccentricity, and load defects can be detected and distinguished for cases where MCSA alone is ineffective. A comparative evaluation between the proposed flux monitoring method and existing methods (MCSA, vibration analysis) is also given.

关键词： cloudy zone   fluctuation   fluidized bed   liquid spray   thermography  

摘要： In a gas-solid fluidized bed with continuous hydrocarbon liquid spray, a volatile "cloudy zone" could be formed, defined as a dynamically steady liquid-affected zone, including droplets, wet particles, and the gas which passes through the zone. A new flow pattern with the dynamic coexistence of cloudy zone and non-cloudy zone (gas-solid zone), is accordingly established. The temperature, particle concentration, and particle velocity fields are measured in real-time via infrared thermography and particle imaging velocimetry, respectively. Results show that the area and range of central position of the cloudy zone illustrate a heavier fluctuant trend with the increasing velocity of liquid spray, and the main frequency of area fluctuation is close to that of the bubble rising. Moreover, the particle concentration and particle velocity in the cloudy zone are lower than those in the non-cloudy zone, breaking the conventional symmetrical distributions of hydrodynamic parameters of particles in a gas-solid fluidized bed.

关键词： Acoustic field   Fine-grained particle content   Fluidized bed   Bed density   Separation performance  

摘要： The bed fluidization characteristics, such as pressure drop, minimum fluidization gas velocity, density, and voidage, play a vital role in understanding the hydrodynamic behavior of fluidization technologies. In this work, the variation in the bed pressure drop was analyzed in presence and absence of an acoustic field. Meanwhile, the minimum fluidization gas velocity was investigated for five different fine particle (-0.074 mm) contents as the acoustic source varied between 90 and 150 Hz, and the sound pressure level was within a range of 100-135 dB. The experimental results show that, upon an increase in the finegrained particle (-0.074 mm) content, the sound frequency and sound pressure level have different effects on the minimum fluidization gas velocity. The introduction of an acoustic wave can effectively ensure the stability of the bed density, thus improving the separation performance of a gas-solid separation fluidized bed, with a lower probable error E. (c) 2021 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.

关键词： catchment management   classification   ecohydrology   flow metrics   hydrographs   river   streamflow   tropical   watershed  

摘要： The Amazon River basin contains a vast diversity of lotic habitats and accompanying hydrological regimes. Further understanding the spatial distribution of flow regimes across the Amazon can be useful for recognizing riverine ecohydrological processes and informing river management and conservation, especially in areas with limited or inconsistent streamflow monitoring. This study compares four inductive approaches for classifying streamflow regimes across the Amazon using an unprecedented compilation of streamflow records from Bolivia, Brazil, Colombia, Ecuador, and Peru. Inductive classification schemes use attributes of streamflow data to categorize river reaches into similar classes, which then may be generalized to understand streamflow behaviour at the basin scale. In this study, classification was accomplished through hierarchical clustering of 67 flow metrics calculated using indicators of hydrologic alteration (IHA) and daily streamflow data from median annual hydrographs (MAHs) for 404 stations (representing >7,000 station-years) across five Amazonian countries. Classification was performed using both flow magnitude-inclusive and flow magnitude-independent datasets. For flow magnitude-independent methods, optimal solutions included six or seven primary hydrological classes for IHA and MAH datasets;for approaches that retained magnitude, variance was sufficiently large to prevent convergence to a specific number of classes. Across methods, class membership was strongly associated with the timing, frequency, and rate of change of flow, and spatially coherent clusters were associated with seasonal, elevational, and stream-order gradients. These results highlight the diversity of flow regimes across the Amazon and provide a framework for studying relationships between hydrological regimes and ecological responses in the context of changing climate, land use, and human-induced hydrological alteration. The methodology applied provides a data-driven approach for

关键词： Gasification   Rice husk   Equivalence ratio   Tar removal   Computational particle fluid dynamics  

摘要： Converting rice husk into energy is a promising method of generating renewable energy and reducing greenhouse gas emissions. The characteristics of rice husk gasification were investigated at an equivalence ratio (ER) of 0.20-0.35 and a gasifier temperature of 700-850 degrees C in a 20-tons-per-day (TPD) bubbling fluidized-bed gasifier system. The optimal conditions of the gasification operation were an ER of 0.20 and gasifier temperature of 800 degrees C. The low heating value of the gas product and cold gas efficiency were 1373.18 kcal/Nm(3) and 70.75%, respectively. After passing the generated gas through the gas cleaning units, it was confirmed that the tar in the product gas was removed with an efficiency of 98%. The cleaned product gas was used for the operation of 400 kW e gas engine. Pressure loss often occurred at the bottom of the gasifier during the gasification operation;we found that the agglomerates generated by the gasification process caused it. Computational particle fluid dynamics simulations were performed to investigate the fluidizing characteristics of agglomerates. To prevent the pressure loss caused by the agglomerates, the stable control of temperature inside the gasifier is needed and an ash removal device remove agglomerates should be installed to maintain stable long-term operation. (C) 2021 Elsevier Ltd. All rights reserved.

关键词： Dry coal beneficiation   Pressure fluctuation   CFD-DEM simulation   Power Spectral Density   Bubble motion  

摘要： Pulsation fluidized bed (PFB) has indisputable advantages for the dry coal beneficiation process. Due to the interaction mechanism between pulsation gas flow and particles is not clear, the regulation of the parameters is still based on empirical method. In this study, the oscillation characteristics of PFB in relation to pressure fluctuations and bubbles motion were studied by both lab experiments and CFD-DEM simulation. Power Spectral Density (PSD) results indicated that dominant frequency of pressure fluctuations was the same as the pulsation frequency of gas flow. In addition, double peaks were clearly formed when the pulsation frequency was set close to the bed natural frequency (about 3.49 Hz). Furthermore, Bubble growth was limited at a moderate frequency (3.49 Hz), but continued to increase at a higher frequency (5.24 Hz). Lab separation experiment also proved that, the pulsation frequency in the middle ranges (especially close to the natural frequency) can significantly improve separation performance. (C) 2021 Elsevier Ltd. All rights reserved.

关键词： buoyancy-driven instability   Hele-Shaw flows  

摘要： The buoyancy-driven chemoconvection induced by a neutralization reaction is theoretically studied for a system consisting of nitric acid and sodium hydroxide aqueous solutions placed in a vertically oriented Hele-Shaw cell. This pair of reactants is a representative case of reacting miscible acid-base systems investigated experimentally in Part 1 of this work (Mizev et al., J. Fluid Mech., vol. 916, 2021, A22.). We showed that the list of the possible instabilities in this system is much richer than previously thought. A new scenario for pattern formation depends on a single parameter denoted by , the reaction-induced buoyancy number defined in Part 1. In this paper, the theoretical analysis complementing the experimental observations provides the conceptual insights required for a full understanding of the mechanisms of the observed phenomena. The mathematical model we develop consists of a system of reaction-diffusion-advection equations governing the evolution of concentrations coupled to the Navier-Stokes equation. The system dynamics is examined through transient linear stability analysis and numerical simulation. If , then a statically stable potential well appears adjacent to the reaction front. As a result, a Rayleigh-Benard-like cellular pattern can arise in this depleted density region. If , then a potential well collapses, and a shock-wave-like structure with an almost planar front occurs. This wave propagates fast compared with the diffusion time and acts as a turbulent bore separating immobile fluid and an area of intense convective mixing. Finally, we determine the place of the above instabilities in an extended classification of known instability types.

关键词： cuprate superconductors   superfluid density   charge density wave   eletronic phase separation   Ginzburg-Landau free energy   Bogoliubov-deGennes superconducting method  

摘要： The superfluid density or superconducting (SC) carrier concentration n(sc) of cuprates has been the subject of intense investigations but there is not any single theory capable to explain all the available data. Here we show that the behavior of n(sc) in under and overdoped cuprates are a consequence of an SC interaction based on charge fluctuations in the incommensurate charge-density-waves (CDW) domains. We have shown that this interaction scales with the CDW amplitude or the pseudogap (PG) energy, yielding local SC amplitudes and Josephson currents. The average Josephson energy EJ rho(sc) proportional to n(sc). We find that n(sc)(p) increases almost linearly with doping p in the underdoped region and in the charge abundant overdoped only a few fractions of the holes condense leading to two kinds of carriers, a recently confirmed feature. The calculations and the rho(sc) data uncover how the PG-CDW-SC intertwined orders operate to yield cuprates properties.