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Abstract High-pressure multistage centrifugal pumps have been widely used in modern industry and required low vibration and noise. In this study, modal analysis of the rotor system of a seven-stage centrifugal pump was carried out numerically by introducing fluid force to ensure that the centrifugal pump would not resonate. A vibration test bench was established to investigate the characteristics with flow rates of 0.8Qd, 1.0Qd, and 1.2Qd, and the vibration data of ten measuring points were collected. The period of the vibration at the bearing was found to be around 20 ms and the period was related to the shaft frequency (SF) and the blade passing frequency (BPF). The vibration of the pump casing was mainly determined by the SF, two times the SF, and two times the BPF. Mechanical motion is the main factor causing pump vibration, and fluid unstable motion is also an important cause.

In this paper, a seven-stage high pressure centrifugal pump for water injection was taken as the research object. The steady state full flow field was numerically simulated by unstructured grid and Renormalization Group (RNG) k - ε turbulence model, and the results were verified by experiment. The flow characteristics of each flow passage component in the centrifugal pump under rated flow condition were analyzed, and the influence of wear-ring clearance flow on the full flow field was studied. The entropy production theory was applied to compare the distribution law of full flow field with and without wear-ring clearance at rated flow. The range and magnitude of the main energy loss in the pump were quantitatively analyzed. The results show that the guide vane area has the highest entropy production, which is the main energy loss part of the centrifugal pump. The existence of wear-ring clearance increases the entropy production of full flow field and has an adverse effect. The impeller wear-ring clearance has a greater influence on the full flow field than the guide vane wear-ring clearance.

Uniform experimental design method is applied to the slow strain rate testing of X12Cr13 stainless steel in natural gas environment. The influence of H2S concentration, CO2 concentration, ambient temperature and pressure on stress corrosion susceptibility are investigated. Through the observation of fracture morphology of the specimens, it is found that the fracture morphology of the specimens is stress corrosion fracture, and there are transgranular, intergranular and mixed fracture. In the fracture energy spectrum analysis, there are many oxides of S and C in the fracture composition, and the content of each element varies greatly with the corrosion environment.

The fatigue test was carried out by simplified lifting method, and the fatigue characteristic curve of X12Cr13 stainless steel at stress ratio of R = 0.1 was plotted at a single point, with the result that the fatigue strength is about 0.5 times the tensile strength. The normal stress ratio R has significant effects on the fatigue life of X12Cr13 stainless steel. As the stress ratio R increases, the fatigue life of the material increases significantly. At the same stress ratio R, the type of fracture morphology of the fatigue specimens is not significantly influenced by the variation of the maximum load. Under the same maximum load condition, larger stress ratio R leads to finer and smoother fatigue fracture surface.

Hydrodynamic cavitation (HC) has been widely considered a promising technique for industrial-scale process intensifications. The effectiveness of HC is determined by the performance of hydrodynamic cavitation reactors (HCRs). The advanced rotational HCRs (ARHCRs) proposed recently have shown superior performance in various applications, while the research on the structural optimization is still absent. The present study, for the first time, identifies optimal structures of the cavitation generation units of a representative ARHCR by combining genetic algorithm (GA) and computational fluid dynamics, with the objectives of maximizing the total vapor volume, Vvapor , and minimizing the total torque of the rotor wall, M→z . Four important geometrical factors, namely, diameter (D), interaction distance (s), height (h), and inclination angle (θ), were specified as the design variables. Two high-performance fitness functions for Vvapor and M→z were established from a central composite design with 25 cases. After performing 10,001 simulations of GA, a Pareto front with 1630 non-dominated points was obtained. The results reveal that the values of s and θ of the Pareto front concentrated on their lower (i.e., 1.5 mm) and upper limits (i.e., 18.75°), respectively, while the values of D and h were scattered in their variation regions. In comparison to the original model, a representative global optimal point increased the Vvapor by 156% and decreased the M→z by 14%. The corresponding improved mechanism was revealed by analyzing the flow field. The findings of this work can strongly support the fundamental understanding, design, and application of ARHCRs for process intensifications.

The distribution and characteristics of internal flow field of the impeller with crack damage in service environment was investigated via numerical simulation with RNG k-ε turbulence model. The diffuser and volute are added based on the original impeller to simulate the internal flow field comprehensively. It was found that along the flow direction, the pressure, velocity, and temperature of the fluid increase continuously, and the maximum value appears near the outlet of the impeller. The maximum pressure and velocity in the crack area are distributed around the middle section and the trailing edge of the crack. Entropy production theory was applied in the study of internal flow, which reveals that the entropy production becomes larger around the crack. The further propagation of the crack is promoted by the opening force perpendicular to the entrance direction of the middle crack, the corrosion propagation at the rear edge of the crack, and the thermal deformation of the blade. The accelerated crack process will finally lead to the blade fracture accident.

The blending effect of gasoline is numerically simulated with different angles of nozzles and rotation speeds based on a rotary jet mixing (RJM) system. The outlet of the RJM system might destroy the components of gasoline, therefore an extra component is firstly added when the RJM system was established. In order to increase the accuracy of the simulation, sliding grid technology is applied and the meshes are divided into different sizes. The radial velocity attenuation curves and Center dynamic pressure attenuation curves of horizontal nozzles, the distribution curves of the cross-section velocity, and velocity nephograms of different blending flow fields were obtained. The results show that the jet property of nozzles and the mixing performance of the RJM system and it can effectively improve the mixing efficiency. Keywords: Gasoline blending, Numerical investigation, Rotary jet mixing system, Mixing time, Jet stirring

Tensile failure process of plane specimens and unilateral V-notched specimens is simulated basing on cohesive zone model (CZM). The internal stress in corrosion scales and film-induced stress in matrix increases with the increase of corrosion scale thickness. The thicker the corrosion scales are, the smaller the crack initiation strength is and the easier to initiate and propagate for stress corrosion cracks are. Meanwhile, with the thickness of corrosion scale increasing, the stress corrosion cracking (SCC) sensitivity of plane specimen increases and KISCC of unilateral V-notch specimens are reduced, making the stress corrosion cracks more likely to propagate. Simulation results show that the stress corrosion cracks nucleate on the surface of corrosion scale and propagate gradually until corrosion scale broke with the continuous tensile load. Finally, stress corrosion cracks propagate into the matrix. Keywords: FV520B stainless steel, Stress corrosion cracking, Slow strain rate tensile test, Cohesive zone model

The energy loss of the multi-stage centrifugal pump was investigated by numerical analysis using the entropy generation method with the RNG k-ε turbulence model. Entropy generation due to time-averaged motion and velocity fluctuation was mainly considered. It was found that the entropy generation of guide vanes and impellers account for 71.2% and 23.3% of the total entropy generation under the designed flow condition. The guide vanes are the main hydraulic loss domains and their entropy generation is about 9 W/K, followed by impellers. There are vortices at the tongue of the guide vane inlet as well as flow separations in the impellers, which lead to entropy generation. The fluid impacts the outer surface of the guide vanes, resulting in the increase in entropy generation. There are refluxes near the guide vane tongues which also increase the entropy generation of this part. The entropy generation distribution of the guide vanes and impellers was investigated, which found that the positive guide vane has more entropy generation compared with the reverse guide. The entropy generation of the blade suction surface is higher compared with the pressure surface. This study indicated that the entropy generation method has distinct advantages in the assessment of hydraulic loss.

Hydrodynamic cavitation is a promising technique for water disinfection. In the present paper, the disinfection characteristics of an advanced hydrodynamic cavitation reactor (ARHCR) in pilot scale were studied. The effects of various flow rates (1.4–2.6 m3/h) and rotational speeds (2600–4200 rpm) on the removal of Escherichia coli (E. coli) were revealed and analyzed. The variation regularities of the log reduction and reaction rate constant at various cavitation numbers were established. A disinfection rate of 100% was achieved in only 4 min for 15 L of simulated effluent under 4200 rpm and 1.4 m3/h, with energy efficiency at 0.0499 kWh/L. A comprehensive comparison with previously introduced HCRs demonstrates the superior performance of the presented ARHCR system. The morphological changes in E. coli were studied by scanning electron microscopy. The results indicate that the ARHCR can lead to serious cleavage and surface damages to E. coli, which cannot be obtained by conventional HCRs. Finally, a possible damage mechanism of the ARHCR, including both the hydrodynamical and sonochemical effects, was proposed. The findings of the present study can provide strong support to the fundamental understanding and applications of ARHCRs for water disinfection.

Hydrodynamic cavitation is a powerful tool for the enhancement of various processing applications. This study utilizes continuous hydrodynamic cavitation (CHC) for the inactivation of pathogens in milk for the first time. The thermal characteristics, inactivation performance, damage on the nutritional composition, product safety, and cost of the advanced rotational hydrodynamic cavitation reactor at pilot scale were comprehensively investigated. The inactivation results demonstrated that 5.89, 5.53, and 2.99 ± 0.08 log reductions of Escherichia coli, Staphylococcus aureus, and Bacillus cereus were achieved, respectively, at a final treatment temperature of 70 °C for 1–2 s. Moreover, the detrimental effect of CHC on the nutritional composition of milk, including mineral, fat, protein, and vitamin contents, was similar to that of high-temperature short-time method. The change in the concentrations of general bacteria and E. coli, as well as the pH value and acidity of the CHC treated milk stored at 5 °C for 14 days was found to be close to that of low-temperature long-time pasteurized milk. The cost of the present CHC treatment was $0.00268/L with a production rate of 4.2 L/min. CHC appears to be a remarkable method for the continuous processing of milk, as well as other liquid foods with high nutrition and “fresh-picked” flavor, due to its high efficacy, good scalability, high production capacity, and low operating and equipment costs.

Hydrodynamic cavitation (HC) has emerged as one of the most potential technologies for industrial-scale water treatment. The advanced rotational hydrodynamic cavitation reactors (ARHCRs) that appeared recently have shown their high effectiveness and economical efficiency compared with conventional devices. For the interaction-type ARHCRs where cavitation is generated from the interaction between the cavitation generation units (CGUs) located on the rotor and the stator, their flow field, cavitation generation mechanism, and interaction process are still not well defined. The present study experimentally and numerically investigated the cavitation flow characteristics in a representative interaction-type ARHCR which has been proposed in the past. The cavitation generation mechanism and development process, which was categorized into “coinciding”, “leaving”, and “approaching” stages, were analyzed explicitly with experimental flow visualization and computational fluid dynamics (CFD) simulations. The changes in the cavitation pattern, area ratio, and sheet cavitation length showed high periodicity with a period of 0.5 ms/cycle at a rotational speed of 3,600 rpm in the flow visualization. The experimental and CFD results indicated that sheet cavitation can be generated on the downstream sides of both the moving and the static CGUs. The sheet cavitation was induced and continuously enlarged in the “leaving” and “approaching” stages and was crushed after the moving CGUs coincided with the static CGUs. In addition, vortex cavitation was formed in the vortex center of each CGU due to high-speed rotating fluid motion. The shape and size of the vortex cavitation were determined by the compression effect produced by the interaction. The findings of this work are important for the fundamental understanding, design, and application of the ARHCRs in water treatment.

The rise of CO2 in the atmosphere, which results in severe climate change and temperature increase, is known as the major reason for the greenhouse effect. Reducing CO2 to value-added products is an attractive solution to this severe problem, along with addressing the energy crisis, to which the catalysts being employed are of vital importance. Due to their high porosity and tunable compositions, metal-organic frameworks (MOFs) show great potential in energy conversion systems. By thermal or chemical treatment methods, the MOFs are easily turned into MOF-derived carbon nanomaterials. The much higher level of conductivity enables MOF-derived carbon nanomaterials to be employed in CO2 conversion processes. The present review, discusses the state of the art of MOF-derived carbon nanomaterials in CO2 electrochemical, photocatalytic, and thermal reduction applications. The corresponding reaction mechanisms and influence of various factors on catalyst performance are elaborated. Finally, the deficiencies and recommendations are provided for future progress.

One of the most challenging issues for the large-scale application of nanomaterials, especially nanocarbons, is the lack of industrial synthetic methods. Sonochemistry, which creates an extreme condition of high pressure and temperature, has been thereby applied for synthesizing a wide variety of unusual nanostructured materials. Hydrodynamic cavitation (HC), characterized by high effectiveness, good scalability, and synergistic effect with other physical and chemical methods, has emerged as the promising sonochemistry technology for industrial-scale applications. Recently, it was reported that HC can not only significantly enhance the performance of biochar, but also preserve or improve the respective chemical composition. Moreover, the economic efficiency was found to be at least one order of magnitude higher than that of conventional methods. Due to the great potential of HC in the industrial-scale synthesis of nanomaterials, the present perspective focuses on the mechanism of sonochemistry, advances in HC applications, and development of hydrodynamic cavitation reactors, which is supposed to contribute to the fundamental understanding of this novel technology.

The influence of pit shape and size on local stress concentration in the tensile specimen and the stress corrosion cracks inception was studied by employing the element remove technique. The maximum stress located in the bottom of pit on FV520B tensile specimen. The location of maximum strain was near the mouth of the pit or the shoulder and plastic strain existed in this region. Stress concentration factor and plastic deformation on four different geometrical shape pits of hemisphere, semi-ellipsoid, bullet and butterfly were numerically investigated, respectively. The simulation results showed that butterfly pit got the biggest stress concentration factor. The plastic strain rate during pit growth was in the sensitivity range of stress corrosion cracks inception, indicating that stress corrosion cracks were more likely to nucleate near the pit tip or the shoulder. Keywords: Stress corrosion crack, Pit shape, Stress concentration factor, FV520B, Element remove technique

Interactions between particles and bubbles have been cornerstone for the successful applications of froth flotation to the beneficiations of minerals or coal. Particle-bubble interactions are highly physio-chemical processes on the basis of surface science and hydrodynamics. Though these two aspects are deeply interwoven, we focus on the discussions of the effects of turbulence on the interactions between particles and bubbles, i.e., collision, attachment and detachment. It has to be mentioned this effect is not working in one direction and can affect flotation performance in a complicated way. Only when turbulence effects are well understood, flotation processes can be optimised by suitably changing equipment structure or operating parameters. The aim of this paper is to review the most recent progresses in this aspect and to identify the future development in successfully considering turbulence effects on flotation processes.

FV520B is a common stainless steel for manufacturing centrifugal compressor impeller and shaft. The internal metal flaw destroys the continuity of the material matrix, resulting in the crack propagation fracture of the component, which seriously reduces the service life of the equipment. In this paper, Abaqus software was used to simulate the prefabricated crack propagation of FV520B specimen with unilateral gap. The results of static crack propagation simulation results show that the maximum value of stress–strain located at the tip of the crack and symmetrical distributed like a butterfly along the prefabricated crack direction, the maximum stress is 1990 MPa and the maximum strain is 9.489 × 10−3. The Mises stress and stress intensity factor KI increases with the increase of the expansion step, the critical value of crack initiation is reached at the 6th extension step. The dynamic crack propagation simulation shows that the crack propagation path is perpendicular to the load loading direction. Similarly, the maximum Mises stress located at the crack tip and is symmetrically distributed along the crack propagation direction. The critical stress range of the crack propagation is 23.3–43.4 MPa. The maximum value of stress–strain curve located at the 8th extension step, that is, the crack initiation point, the maximum stress is 55.22 MPa, and the maximum strain is 2.26 × 10−4. On the crack tip, the stress changed as 32.24–40.16 MPa, the strain is at 1.292 × 10−4–1.897 × 10−4. Keywords: FV520B, Crack propagation, Mises stress, Stress–strain, Numerical investigation

The electrochemical corrosion of the FV520B stainless steel for natural gas compressor impeller is studied by means of the uniform experimental method. The electrochemical corrosion potential, current density and Tafel slope of the material are measured, and the polarization resistance is solved. The experimental results show that FV520B material does not appear passivation area in the presence of the natural gas environment with H2S, and the material has been in the activation and dissolved state. When the temperature is below 130 °C, the corrosion is dominated by the process of the anode reaction, the concentration of H2S is the decisive factor to determine the occurrence of stress corrosion, the increase of H2S concentration significantly accelerates the corrosion process of the specimen, CO2 inhibits the occurrence of the stress corrosion to a certain extent. Keywords: FV520B, Stress corrosion, Electrochemical corrosion, Natural gas

There exits multiphase flow of oxygenized air, lime slurry and limestone particles in power plant flue gas desulfurization (FGD) system. A rotary jet stirring device (RJSD) is installed in the slurry pond at the bottom center of absorption tank to get an appropriate mixing flow field so far as possible to get off sulfur dioxide. By employing the standard k-ε turbulence model and the Eulerian multiphase model, numerical investigations for liquid-solid and liquid-solid-gas flow field are presented to discuss the distribution of flow hydrodynamic parameters under a certain operational condition, respectively. In liquid-solid flow, limestone particle concentration shows a decreasing trend with the increase of the rotation angular velocity. The core jet length of the rotary mixer tend to be much longer with the increase of jet velocity under the surrounding pressure, but the dispersed slurry velocity tends to reduce after an initial increasing during the starting period due to the inadequate mixing process. This phenomenon shows that the stirring down-stream is more important than the advection stream in liquid-solid condition. Compared to the liquid-solid condition, the distribution of the air volume of fraction in gas-liquid-solid flow is getting uniform because of the participation of the solid phase, and the down-stream plays an important role in air lateral distribution. The concentration of the limestone particle in liquid-solid condition is higher than in the multiphase flow field. The reason is that the particle distributing velocity near the tank wall is lower and the vertical velocity is higher than in the liquid-solid condition when the jet down-stream velocity is equal. The numerical results could be a useful exploration for an attempt usage of rotary jet device in FGD system. Keywords: Flue gas desulfurization, Lime slurry pond, Jet stirring, Rotary jet

The stress corrosion cracking (SCC) behavior of AISI347 austenitic stainless steel exposed to acid solution containing chloride ion at different temperature and pressure is studied through slow strain rate testing (SSRT) at different test condition. The result of SSRT shows, with the pressure increasing, the SCC resistance is getting worse and the trend of brittle fracture presented by the fracture surface is more obvious. With the temperature rising, the mechanical properties of AISI347 getting worse first and then getting better, it gets to be the worst when the temperature is 260 °C. The result of significance effect analysis of temperature and pressure on SCC shows that the temperature has a greater effect on the resistance to SCC of AISI347 austenitic stainless steel than the pressure. The main component of passive film is analyzed and the mechanism of SCC is discussed. Chromium oxides soluble in the acidic chloride solution results in the forming of corrosion pits and the cracking of the passive film under stress. Keywords: Stress corrosion cracking, Chloride ion, Slow strain rate testing, AISI347

FV520B steel is a kind of precipitation hardening Martensitic stainless steel, it has high-strength, good plasticity and good corrosion resistance. Stress corrosion cracking (SCC) is one of the main corrosion failure mode for FV520B in industrial transportation of natural gas operation. For a better understanding the effect on SCC of FV520B, the improved wedge opening loading (WOL) specimens and constant displacement loading methods were employed in experimental research in carbon dioxide and hydrogen sulfide solution. The test results showed that the crack propagation rate is 1.941 × 10−7–5.748 × 10−7 mm/s, the stress intensity factor KISCC is not more than 36.83 MPa m. The rate increases with the increasing of the crack opening displacement. Under the condition of different initial loading, KISCC generally shows a decreasing tendency with the increase in H2S concentration, and the crack propagation rate showed an increasing trend substantially. For the enrichment of sulfur ion in the crack tip induced the generation of pitting corrosion, promoting the surrounding metal formed the corrosion micro batteries, the pit defects gradually extended and connected with the adjacent pit to form a small crack, leading to further propagation till cracking happened. Fracture microscopic morphology displayed typical brittle fracture phenomena, accompanying with trans-granular cracking, river shape and sector, many second cracks on the fracture surface. Keywords: FV520B, Wedge opening loading specimen, Stress corrosion cracking, Hydrogen sulfide

The flue-gas desulfurization model was studied through computational fluid dynamics software. The oxidation air was asymmetrically pumped into the slurry pond. A rotary jet mixing system was established at the bottom center of the pond to agitate the lime slurry. The Navier–Stokes equation as the control equation, the standard k–ε turbulence model, sliding grids structure, and three-dimensional Eulerian multiphase flow of lime slurry were used for the numerical simulation. The independence of the meshes and the time step was verified. The distribution of the concentration of oxidation air and influents on the velocity of flow was analyzed with five angular velocities (0.01, 0.10, 0.20, 0.50, and 1 rad/s) for the rotary jet mixing. The simulation results showed that the angular velocity has a great influence on the velocity of the slurry and the distribution of the oxidation air.

The preference for particles to accumulate at specific regions in the near-wall part is a widely observed phenomenon in wall-bounded turbulence. Unlike small particles more frequently found in low-speed streaks, finite-size particles can accumulate in either low-speed or high-speed streaks. However, mechanisms and influencing factors leading to the different preferential concentration locations still need to be clarified. The present study conducts particle-resolved direct numerical simulations of particle-laden turbulent channel flows to provide a better understanding of this seemingly puzzling behaviour of preferential accumulation. These simulations cover different particle-to-fluid density ratios, particle volume fractions, particle sizes and degrees of sedimentation intensity. We find that the large particle size is the crucial factor that results in particles accumulating in high-speed streaks. Large particles not only are difficult to be conveyed by the quasi-streamwise vortices to low-speed streaks but also can escape from the near-wall region before moving spanwisely out from high-speed streaks. The sedimentation effect allows particles to gather closer to the channel wall and stay longer in the near-wall regions, reinforcing the sweeping mechanism of quasi-streamwise vortices that transport particles from high- to low-speed streaks. As a result, sedimenting particles tend to accumulate in the low-speed streaks. [ABSTRACT FROM AUTHOR]