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Extreme environmental changes caused by the cavitation bubble collapse, such as high pressure, high temperature and the microjet, will cause pyrolysis reaction at the gas and liquid interface inside the bubble. Self-excited pulsed cavitation jet has an instantaneous strong pulse pressure, which leads to local hot spots surrounding the cavitation bubbles. The generation of strong oxidizing free radicals promotes easy ozone conversion into oxygen. Numerical simulations were conducted for ozone decomposition by cavitation jet. Three groups of different collision angles were applied to compare and analyze the ozone degradation reaction. Results showed that the collision angle has a certain influence on the chemical reaction intensity, the degradation of ozone, and oxygen production. At the collision angle of 180°, the chemical reaction was the most violent, with ozone degradation and oxygen production at the highest level, followed by 120° and lowest at 90°.

Shield pumps which transport a variety of complex media are widely used in chemical industry, mineral industry, and other fields. However, the hard particles in the media erode the flow passage in the shield pump, seriously affecting the service life of the pump. Therefore, it is important to study the erosion process in the flow passage to extend the service life of the pump. This erosion process in the shield pump can be investigated by experiments, but it is difficult for the current experimental method to copy the real industrial service environment of impellers. For example, the environment temperature and speed range are found difficult to be reached by the current experimental method. Comparatively, the simulation by finite element method can overcome the above deficiency. In this article, the ANASYS software is used to simulate the erosion process in shield pump flow passage due to hard particles. Specifically, the structural static analysis module is used to build the model of thermal barrier coating components and hard particle components. Then the variation law of stress, strain, and material deformation of the flow passage components under concentrated force is obtained. Second, the extended finite element method is used to study the crack propagation caused by the erosion process. A linear elastic–linear softening constitutive model is established to simulate the stress variation during the crack propagation and material removal under the continuous erosion from hard particles. The proposed law regarding stress variation and crack propagation in the erosion process in this study contributes to theoretical support for damage detection and service life extension of shield pumps.

In this article, the side-entry agitator commonly used in the wet desulfurization absorption tower of a 300 MW thermal power unit was taken as the research object, and the gas–liquid two-phase flow field in the stirring tank was numerically simulated by using the two-fluid model based on Euler–Euler method. The vertical and horizontal velocity field distribution and gas phase distribution in the stirring tank were studied. The results showed that the side-entry agitator formed a “fountain” circulating flow in the stirring tank. The high-speed region of the liquid flow was mainly concentrated near the mixing blade and the bottom banded region. The range of large changes in the fluid velocity was mainly concentrated from the bottom of the mixing tank to 2–3 m from the bottom. The distribution of the oxidizing air was concentrated in the middle of the stirring tank. The mixing effect of two phases in the stirred tank was good, and the oxidizing air was fully diffused. The numerical study in this article has reference significance for in-depth understanding of the flow field and mixing effect of the side-entry agitator.

The turbulent energy dissipation rate is an important parameter that determines the transfer rates of mass, heat and momentum in chemical engineering industry. Especially in a multiphase reactor, the local instantaneous turbulent dissipation rate affects the breakage and coalescence of bubbles or droplets. To directly determine the local turbulent dissipation rate, fluctuating velocity gradients have to be measured down to the Kolmogorov length scale. This paper compares the advantages and disadvantages of three different methods, namely, correlation method, optical flow method and hybrid method, in the evaluation of velocity fields, which are subsequently used to calculate the turbulent dissipation rate. An instantaneous flow field of homogeneous isotropic turbulence from DNS results is used as a benchmark. The velocity field and turbulent dissipation rate field obtained by these three methods are compared to the DNS results. It is shown that the hybrid method performs better in both velocity field evaluation and local turbulent dissipation rate estimation compared to the other two methods. This is because the hybrid method combines the advantages of the correlation method in achieving a stable averaged velocity field and the optical flow method in achieving pixel-level resolution measurement of the flow field.

Electric rotary kiln is one of the key equipment in the chemical industry, which is mainly used for heating materials. In the current research, the heat calculation method of the electric rotary alumina kiln is constructed, and the heat transfer processes in the furnace, the furnace tube, and the furnace tube wall are systematically analyzed. The theoretical model of the electric rotary alumina kiln is established and solved by the fourth-order Runge–Kutta method, and the temperature rise curves in the kiln are obtained. The numerical simulation is carried out to investigate the temperature distribution of materials and gases in the furnace tube. It is revealed in the results that the temperature distribution of the electric rotary alumina kiln is more uniform than that of the internal rotary kiln, and the stable operation state can be reached in a very short time, which means that reduced furnace tube length and reduced production cost can be achieved under the same roasting requirements.

A particle-resolved study of a collision system composed of heavy particles and light particles in a homogeneous isotropic turbulence has been performed. Direct numerical simulations (DNS) of this system were conducted using lattice Boltzmann method (LBM). The effects of hydrodynamics on the collision particles were accounted by directly resolving the flow around finite-size particles with an interpolated bounce-back scheme. A large-scale stochastic forcing scheme was implemented within the mesoscopic multiple-relaxation-time LBM approach to maintain turbulence intensity at targeted levels. Both kinematic and dynamic collision kernels were evaluated to study the correlation of total collision events and turbulent kinetic energy (TKE) dissipation rate. The results show that collisions between particles increase with the increase of TKE dissipation rate as radial relative velocities between particles increase with it. It is found that the dynamic collision kernels do not match with the kinematic collision kernels which is derived from point-particle method. Quantitatively, they were approximately 4 to 10 times smaller than the corresponding dynamic collision kernels. Therefore, it is not reasonable to estimate the kinematic collision kernel in particle-resolved simulations as its rationales are not valid. However, the collision behavior can still be accounted for by means of the dynamic collision kernel since it is obtained from the direct statistical analysis of the collision events.

Periodical dynamic characteristics induced by geometric parameters and operational variables of the self-excited pulsed cavitation jet under the optimum experimental condition is analyzed in the present study. The mechanism of cavitation jet occurrence is interpreted by combining the jet shape, the striking force, and the cavity pressure. With the increase of the inlet pressure, the pulsed frequency increases, and the amplitude decreases. Besides, the pulsed frequency decreases, and the amplitude increases as the oscillation chamber length gets much longer. It reflects that the shape and trend of the waveform are different under different structural parameters and the same operating pressure, while the waveform is the same with the same nozzle structure parameters and the various operating pressures. The peak bandwidth of the waveform is reduced with the increase of the pressure. A long enough peak bandwidth has an essential effect on the striking work operation. Only the peak value of the strike force is kept for an extended period so that it can get an effective strike. The waveform of all dynamic characteristics in the pulsed jet is harmonic. These harmonic waves can be seen as the superposition of several sine waves or cosine waves. It is required that the dominant frequency of pressure oscillation waves is single to avoid the negative influence of noise waves, and then a better effect of striking force is obtained.

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.

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 Lattice Boltzmann and point particle methods are used to conduct direct numerical simulations of the collisions between particles and bubbles in homogeneous isotropic turbulence. Particle-bubble collision is a complicated process affected by many factors, and the effects of the turbulent flows and the parameters of a particle-bubble system on the collision process are studied. The effects of the preferential concentrations of particles and bubbles in the turbulent flows on the collision process are studied from the perspective of radial distribution functions. To maintain background turbulent flows at targeted turbulent levels, a non-uniform time-dependent large-scale stochastic forcing scheme was implemented within the mesoscopic multiple-relaxation-time LBM approach. A local peak was found in the radial distribution function when the parameters of the particle-bubble system or turbulent levels were changed. Nevertheless, the peak was not found in the collision kernel function as the effect of the preferential concentration was overwhelmed by the effect of the radial relative velocity. It is interesting to find that the distributions of particles and bubbles were affected by the turbulent energy dissipation rate in a way that local accumulations were most apparent when the Stokes number of particles was 1. Nevertheless, the radial distribution functions of particle-bubble pairs remained stable at 1 in the turbulent flows with varied turbulent energy dissipation rates. This means that the distributions of particles and bubbles are not correlated and the effects of individual preferential concentrations of particles and bubbles on the collisions between particles and bubbles are weak. Therefore, the collision kernels of particle-bubble pairs increased with turbulent energy dissipation rate in a similar way as the radial relative velocities between particles and bubbles increased with turbulent energy dissipation rate.

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.

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.

Graphical abstract, Highlights • Rapid disinfection of water containing E. coli is obtained by a pilot-scale ARHCR. • The ARHCR can cause serious cleavage and surface damages to E. coli. • Proposed disinfection mechanism includes hydrodynamical and sonochemical effects., 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.

Graphical abstract, Highlights • Cavitation flow in an ARHCR is studied combining flow visualization and CFD. • Cavitation is characterized by the periodic motion of CGUs. • Cavitation development process shows high periodicity from flow visualization. • Vortex cavitation is generated at the vortex center of CGUs. • Sheet cavitation is induced in the flow separation region of downstream CGUs., 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.

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 economical efficiency was found to be as 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.

Disinfection, which aims to eliminate pathogenic microorganisms, is an essential step of water treatment. Hydrodynamic cavitation (HC) has emerged as a promising technology for large-scale disinfection without introducing new chemicals. HC, which can effectively induce sonochemistry by mechanical means, creates extraordinary conditions of pressures of ~1000 bar, local hotspots with ~5000 K, and high oxidation (hydroxyl radicals) in room environment. These conditions can produce highly destructive effects on microorganisms in water. In addition, the enhancements of chemical reactions and mass transfers by HC produce the synergism between HC and disinfectants or other physical treatment methods. HC is generated by hydrodynamic cavitation reactors (HCRs), therefore, their performance basically determines the effectiveness, economical efficiency, and applicability of HC disinfection. Therefore, developing high-performance HCRs and revealing the corresponding disinfection mechanisms are the most crucial issues today. In this review, we summarize the fundamental principles of HC and HCRs and recent development in HC disinfection. The energy release from cavitation phenomenon and corresponding mechanisms are elaborated. The performance (effectiveness, treatment ratio, and cost) of various HCRs, effects of treatment conditions on performance, and applicability of HC disinfection are evaluated and discussed. Finally, recommendations are provided for the future progress based on the analysis of previous studies.

A comprehensive review of the published literature regarding the computational fluid dynamics (CFD) modelling of the flotation process is presented. The detailed principles, mechanism and operation of the flotation process are discussed focusing mainly on the hydrodynamic aspect which is required for the successful operation of the flotation cell. The kinetic modelling of flotation process has been reviewed in detail in three major flotation equipment namely mechanically agitated flotation cell, flotation column and dissolved air flotation. The advances made in the modelling and simulations of the equipment have been critically analyzed. Specific emphasis is given on the bubble-particle interactions and the effect of turbulence on these interactions. An attempt has been made to correlate the model parameters with the turbulence parameters. A thorough discussion is presented to highlight strengths and weaknesses of currently used CFD models and the recent developments in the numerical simulation tools for better understanding of the process. Finally, recommendations have been made for the future progress based on the analysis of the previous work.

For the welded joint specimens of the steel FV520B used in natural gas impellers, the uniform experimental method is applied in the experiment of electrochemical corrosion potential (ECP) under a certain concentration of H2S and CO2, temperature and pressure to get some test data including electrochemical corrosion potential, current density, Tafel slope and polarization resistance. In addition, the stress corrosion susceptibility index has been measured by the experimental of slow strain rate tensile (SSRT). Combined with observation of crack and fracture morphology, the stress corrosion cracking mechanism of the martensitic stainless steel FV520B welded joints in the service environment is explored. The experimental results show that there are obvious tendency of stress corrosion cracking in welded joints and the relatively significant effects of temperature and CO2 concentration on corrosion current density and stress corrosion susceptibility. In the environment of 98 °C, 6 MPa, 30% H2S and 65% CO2, the stress corrosion susceptibility of welded joint specimens is the highest, and the fracture surfaces display brittle fracture behavior.

Graphical abstract, 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.

Rotary jet agitator is an effective device for mixing, dispersing, dissolving, and suspending dispersed phases in liquid, and is particularly advantageous to the homogenization of oxygen-enriched air within the lime slurry desulfurization system. The distribution of oxygen-enriched air in agitators is vital for the process of gypsum crystallization and the homogeneous and sufficient oxygen-enriched air can promote the formation of an economically useful by-product. The present study investigated the diffusion performance of oxygen-enriched air in a rotary jet agitator during the wet flue gas desulfurization process by utilizing computational fluid dynamics. The consistency of numerical and experimental results is validated under identical conditions. Investigation results show that the rotation velocities and the inlet velocities of rotary jet machines significantly affect the distribution and homogeneity of the oxygen-enriched air distribution. However, these effects deteriorate with increasing rotation angular and jet outlet velocities. Under the optimal condition, the oxygen-enriched air concentration, within the cross-sections, fluctuates by approximately 20%. The Rotary jet agitator appears to be a remarkable method for the homogenization of oxygen-enriched air in the lime slurry tank, and in other gas-liquid stirring tanks, due to its high efficacy and good stirring effect.

A variety of geometric sizes of a self-excited pulsed jet such as the diameter of the suction and discharge nozzle, jet chamber length and diameter, and the collision angle are the main structural parameters. Under certain operating conditions at a given fluid flow rate, target space, and dynamic head, the jet strike force amplitude and frequency were significantly influenced by these structural sizes. Twenty five group orthogonal experiments were designed to explore the jet dynamic performance with structural sizes to find which group was the best combination. The experiment employed five levels of the diameter of the suction and discharge nozzles, three levels of the chamber diameter, and five levels of the length of the chamber and collision angles. Experimental results showed that the suction nozzle diameter was the most important parameter influencing the jet performance. The next was discharge nozzle diameter. The other three sizes of chamber diameter and length, and collision angle had the similar effect on the self-excited pulsed jet. The results can have guiding significance for the design of self-excited pulsed cavitation nozzles.

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