The multistage centrifugal pump is the critical component of mineral resources lifting in deep-sea mining. The reflux of nodules in the lifting pipe caused by the emergency pump stop can easily cause the pump to clog. In this paper, coupled Computational Fluid Dynamics and Discrete Element Method (CFD-DEM co-simulations) are used to clarify the solid-liquid two-phase flow in two-stage centrifugal pumps under different particle sizes (10–20, 20–30, 30–40, 40–50 mm) with constant particle concentration. The movement and accumulation behaviour of particles in different flow fields (pipeline to pump, the first to the second pump stage) is investigated. Meanwhile, the effect of particle size and particle reflux velocity on the blockage of the flow channel in the pump was investigated. Particle accumulation in the pump was observed to determine the key factors affecting the pump’s reflux capacity. The residual mass of particles in the pump at different particle sizes was counted. Simultaneously, the percentage of residual mass of 10–20 mm particles in the pump was compared between the experiment and the simulation with an acceptable tolerance of within 10%. In addition, pressure changes in the blockage-prone section were also investigated. A comparison between experiments and simulations verifies the consistency of the trend on the pump inlet pressure when clogged with 50 mm particles. It was found that larger particles in the range of 10–30 mm can better ensure the pump’s reflux performance.

CFD-DEM Simulation of Backflow Blockage of Deep-Sea Multistage Pump

In this paper, the mechanism of rotor-stator interaction in a centrifugal pump with guide vanes is studied numerically and theoretically. The dynamic mode decomposition method is employed to decouple and reconstruct the unsteady flow. A diametrical mode theory suitable for centrifugal pumps with guided vanes is proposed to determine the source of harmonics with higher amplitudes quickly. The results show that the dominant frequencies of the pressure pulsation in the volute and guide vanes are the blade passing frequency and its harmonic frequencies, and the corresponding flow structure is stable and has higher modal energy. The rotor-stator interaction effect around the impeller outlet is most pronounced. The potential flow effect works on the impeller and guide vanes but decays rapidly. The pressure pulsation caused by the wake effect propagates downstream and persists for long distances, which is the main reason for forming the modal pressure field in the volute. The modal reconstruction can reproduce the dynamic evolution process of the pressure field at the characteristic frequencies. The propagation characteristics of the modal pressure field in the volute can be accurately predicted by theoretical analysis. This research can provide an essential reference for fault diagnosis and vibration control of the centrifugal pump.

Mechanism of the rotor-stator interaction in a centrifugal pump with guided vanes based on dynamic mode decomposition

Cement composites, including cement and mortar, are now the most commonly used building components, and thus an extreme and durable emphasis is being articulated. Unique nanoscale fibres, such as carbon nanotubes (CNTs) and graphene oxide (GO), have recently developed to open up new possibilities to boost cement composite performance. GO is a mono-atomically two-dimensional thick carbon allotropic structure that emerged as a 21st-century innovative material. It has been granted global attention owing to its extraordinary transport, thermal, optical, and mechanical properties. Tailoring the properties of cementitious composites with GO-nanomaterial regulates not only the secondary hydration mechanism but also boosts the mechanical performance, durable behaviour, self-healing, and other multifunctional properties. The influence of GO presents an astounding and distinctive performance such as enhancement of gel pores, reduction in larger capillary pores, bridging the microcracks and resisting its propagation, strengthening the overall cement composite performance. This article attempts to present a substantial review of the functioning of cement composites reinforced with GO nanomaterial. 

Nano-cementitious composites modified with Graphene Oxide – a review

Stability dynamics in pumps is a key problematic issue which needs to be critically looked at. For instance, in side channel pump, pressure fluctuations and unsteady forces characteristics are inevitable in the clearances and this strongly affects the flow and pressure stability. Therefore, the research work herein seeks to numerically investigate the pressure fluctuation intensity in the clearances and characterize the axial and radial forces distributions around the impeller under different blade suction angles. Three impeller schemes 1, 2, and 3 are modeled with blade suction angles 10°, 20°, and 30°, respectively. Based on the reliable standard SST k-ω turbulent flow model, the unsteady flow state of the side channel pump was obtained by numerical simulation and further verified by experiment results. Variations in amplitude and frequency at different monitoring points in the clearances were observed in both time and frequency domain for each impeller scheme. The findings elucidate that pressure fluctuation intensity in the clearances is significantly different for all the impeller schemes. Obvious asymmetrical distribution of fluctuation magnitudes was noticeable in the axial and radial clearance. Generally, the amplitude of pressure fluctuation intensity of impeller scheme 1 and 2 is substantially reduced compared to impeller scheme 3. Also, impeller scheme 1 exerts the smallest magnitude of axial and radial force. However, when the pump operates under impeller scheme 3, the amplitude of the forces increases significantly. This study provides a solid foundation for the reduction of pressure fluctuations, vibration, and noise performance in side channel pumps.

Study on the inner flow mechanisms and unsteady force distribution of side channel pump

The effect of deep cryogenic treatment (DCT) on the artificial ageing kinetics of a SiC particles reinforced aluminum alloy composite (SiCp-Al) is experimentally studied in this paper. The evolutions of both macro-properties (i.e., yield strength and ultimate tensile strength) and microstructures (precipitates) have been investigated by a set of hardness tests, tensile tests, and microstructural observations (scanning electron microscope, SEM and transmission electron microscope, TEM) for a SiCp-Al composite material with conventional heat treatment (solution heat treatment + quenching + artificial ageing, CHT) or DCT (solution heat treatment + quenching + deep cryogenic + artificial ageing). The results show that SiCp could significantly accelerate the ageing kinetics of the composites. Meanwhile, compared with CHT conditions, DCT can further improve the yield strength (YS) and ultimate tensile strength (UTS) of the composite materials after artificial ageing. The microstructures show that DCT induces the generation of more thinner θ’ precipitates homogeneously distributed in the grains during artificial ageing compared with corresponding CHT conditions. A quantified analysis has been performed based on the microstructural data, and the calculated results further support the indication that the strengthening effect in DCT compared with CHT is mainly contributed by corresponding precipitation behavior.

/pdf/effect-of-deep-cryogenic-treatment-on-the-artificial-ageing-27towu5q.pdf

Effect of Deep Cryogenic Treatment on the Artificial Ageing Behavior of SiCp–AA2009 Composite

The pressure fluctuation inside centrifugal pumps is one of the main causes of hydro-induced vibration, especially at the blade-passing frequency and its harmonics. This paper investigates the feature of blade-passing frequency excitation in a low-specific-speed centrifugal pump in the perspective of local Euler head distribution based on CFD analysis. Meanwhile, the relation between local Euler head distribution and pressure fluctuation amplitude is observed and used to explain the mechanism of intensive pressure fluctuation. The impeller blade with ordinary trailing edge profile, which is the prototype impeller in this study, usually induces wake shedding near the impeller outlet, making the energy distribution less uniform. Because of this, the method of reducing pressure fluctuation by means of improving Euler head distribution uniformity by modifying the impeller blade trailing edge profile is proposed. The impeller blade trailing edges are trimmed in different scales, which are marked as model A, B, and C. As a result of trailing edge trimming, the impeller outlet angles at the pressure side of the prototype of model A, B, and C are 21, 18, 15, and 12 degrees, respectively. The differences in Euler head distribution and pressure fluctuation between the model impellers at nominal flow rate are investigated and analyzed. Experimental verification is also conducted to validate the CFD results. The results show that the blade trailing edge profiling on the pressure side can help reduce pressure fluctuation. The uniformity of Euler head circumferential distribution, which is directly related to the intensity of pressure fluctuation, is improved because the impeller blade outlet angle on the pressure side decreases and thus the velocity components are adjusted when the blade trailing edge profile is modified. The results of the investigation demonstrate that blade trailing edge profiling can be used in the vibration reduction of low specific impellers and in the engineering design of centrifugal pumps.

Pressure Fluctuation Reduction of a Centrifugal Pump by Blade Trailing Edge Modification

Effect of deep cryogenic treatment on mechanical properties and residual stress of AlSi10Mg alloy fabricated by laser powder bed fusion

The traditional construction technology not only has environmental friendly problems such as noise and dust but also has resource-saving problems such as large template quantity and low construction accuracy. In addition, the traditional construction technology has an insurmountable technical bottleneck in the construction of special-shaped buildings. Building 3D printing technology can effectively overcome many problems existing in traditional construction technology and provide unlimited possibilities for the construction of special-shaped buildings. Concrete 3D printing technology is one of the most important technical categories of building 3D printing. In this study, the research status and progress of concrete 3D technology were reviewed from the aspects of equipment system, materials, defect control, and application scenarios. On this basis, the development foreground was prospected.

https://downloads.hindawi.com/journals/je/2022/6882386.pdf

Dongqing Qian

Papers

Pressure Fluctuation Reduction of a Centrifugal Pump by Blade Trailing Edge Modification

Effect of deep cryogenic treatment on mechanical properties and residual stress of AlSi10Mg alloy fabricated by laser powder bed fusion

Research Progress of Concrete 3D Printing Technology and Its Equipment System, Material, and Molding Defect Control