Cavitation Reactor Research Articles

Experimental research on supercavitation in jet pump cavitation reactors for zero flow-ratio conditions

We report an experimental study of cavitating flow in a jet pump cavitation reactor (JPCR) with a special emphasis on the supercavitation stage with a tubular supercavitation cavity. This study focuses on the evolution and characteristics of the cavitation for the zero flow-ratio conditions and the supercavitation mechanism. The results show that increasing the limiting flow ratio qr leads to shearing cavitation, which transforms into supercavitation when qr = 1. A cloud cavity forms at the end of the tubular supercavitation cavity and then sheds and collapses downstream. In addition, a wall-attached reentrant jet appears upstream. The results show that the diffuser diffusion angle β, the throat-length–diameter ratio Lth/Dth, and the throat-nozzle area ratio m all significantly affect the stability of the supercavitation cavity, with m and Lth/Dth significantly impacting the characteristic length L/Dth. The supercavitation cavity is induced by the high-speed jet entrainment and the shear layer between the jet and the surrounding water. It is then maintained by the momentum balance in the JPCR. The pressure pulsations are small in the supercavitation cavity and become significantly stronger where the cloud cavity collapses because the high-speed jet retains more energy.

Cavitation Reactor for Pretreatment of Liquid Agricultural Waste

One of the most well-known methods of intensifying the process of anaerobic digestion is the pretreatment of raw materials. For the first time, the use of a jet-driven Helmholtz oscillator for biomass pretreatment is proposed. The design of the device is optimal for creating hydraulic cavitation; however, in this case, acoustic oscillations are generated in the system and resonance occurs. In this study, the optimal design of this device was determined for the subsequent design of a cavitation reactor. The diameter of the resonant chamber was varied in the range from 28.3 to 47.5 mm, and its length from 6 to 14 mm; in addition, the diameter of the outlet was changed from 6.1 to 6.3 mm. Based on the experimental data obtained, it was found that the optimal ratio of the length of the resonator chamber to the diameter of the inlet nozzle is 1.73, and the inner diameter of the resonator chamber to the diameter of the inlet nozzle corresponds to 5.5. Improving the technology of agricultural waste disposal will ensure their maximum involvement in economic circulation, reduce the consumption of traditional fuel and energy resources, and improve the technological and machine-building base, which makes it possible to produce competitive cavitation reactors.

Investigation of free fatty acid reduction from mixed crude palm oil using 3D-printed rotor–stator hydrodynamic cavitation: An experimental study of geometric characteristics of the inner hole

A continuous esterification process is employed to decrease the free fatty acid (FFA) concentration of FFA-rich mixed crude palm oil. Both optimal and recommended conditions are determined for the esterification reaction conditions and the geometry of the 3D-printed rotor design in the rotor–stator hydrodynamic cavitation reactor. This study is primarily concerned with the effect of the cavitation device configuration, especially the rotor design, on FFA reduction. Instead of conventional spherical or cylindrical drilled holes, a point angle cone-shaped hole is used to create cavities over the rotor surface. These point angles are adjusted to clarify their effect on FFA reduction. The response surface methodology is applied to determine the optimal concentrations of methanol and sulfuric acid, rotor speed, hole diameter and depth, and cone point angle. The recommended conditions are 20.8 wt% methanol, 2.6 wt% sulfuric acid, 3000 rpm, 5 mm hole diameter, 5 mm hole depth, and 110°, respectively. Under this configuration, the FFA content is reduced from 12.014 wt% to around 1 wt%. A maximum yield of 97.34 vol% esterified oil is obtained through a completed phase separation step, and 93.31 vol% pure oil is collected after the cleansing step. The recommended conditions result in reduced chemical usage, cheaper FFA reduction, and lower environmental impact. This creative rotor design effectively improves our understanding of the geometry of the cavitation device, thus enhancing the cavitation effect in industrial operations.

Optimized Geometric Structure of a Rotational Hydrodynamic Cavitation Reactor

The objective of this paper is to obtain an excellent structure of a rotational hydrodynamic cavitation reactor (RHCR) by a numerical method and then to investigate the cavitating flow characteristics of the optimized RHCR experimentally. The RNG k-ε turbulence model combined with the Zwart cavitation model was applied to analyze the influence of the straight blade number, the baffle position and the baffle shape on the pressure field, bubble distribution and turbulence kinetic energy of the RHCR. The results show that compared to the original model, an RHCR with a straight blade number of 6, a baffle position of 0.74 and a triangular baffle offers better cavitation performance. Moreover, the energy performance and the cavitation development process of the optimized RHCR were studied experimentally. The results indicate that the multiscale bubbles are induced by straight blades and baffles of the optimized RHCR, accompanied by the twice quasi-periodic shedding dynamics in one cycle. The findings of this study have positive significance for the design and optimization of RHCRs.

Investigation of cavitation noise using Eulerian-Lagrangian multiscale modeling

We have employed the large eddy simulation (LES) approach to investigate the cavitation noise characteristics of an unsteady cavitating flow around a NACA66 (National Advisory Committee for Aeronautics) hydrofoil by employing an Eulerian-Lagrangian based multiscale cavitation model. A volume of fluid (VOF) method simulates the large cavity, whereas a Lagrangian discrete bubble model (DBM) tracks the small bubbles. Meanwhile, noise is determined using the Ffowcs Williams-Hawkings equation (FW-H). Eulerian-Lagrangian analysis has shown that, in comparison to VOF, it is more effective in revealing microscopic characteristics of unsteady cavitating flows, including microscale bubbles, that are unresolvable around the cloud cavity, and their impact on the flow field. It is also evident that its evolution of cavitation features on the hydrofoil is more consistent with the experimental observations. The frequency of the maximum sound pressure level corresponds to the frequency of the main cavity shedding for the noise characteristics. Using the Eulerian-Lagrangian method to predict the noise signal, results show that the cavitation noise, generated by discrete bubbles due to their collapse, is mainly composed of high-frequency signals. In addition, the frequency of cavitation noise induced by discrete microbubbles is around 10 kHz. A typical characteristic of cavitation noise, including two intense pulses during the collapsing of the cloud cavity, is described, as well as the mechanisms that underlie these phenomena. The findings of this work provide for a fundamental understanding of cavitation and serve as a valuable reference for the design and intensification of hydrodynamic cavitation reactors.

Chain-length dependent ultrasonic degradation of perfluoroalkyl substances

Per- and polyfluoroalkyl substances (PFAS) have been found all over the world and are particularly persistent, potentially carcinogenic, and bioaccumulative in the environment. Degradation of short-chain perfluorinated carboxylic acids of varying carbon chain lengths (from 4 to 8 carbons), higher-chain perfluoro carboxylic acids of varying carbon chain lengths (from 9 to 14 carbons), and perfluorosulfonic acids of varying carbon chain lengths (6 and 8 carbons) were tested in a flow through ultrasonic cavitation reactor to determine the efficacy of the high frequency ultrasound process. Temperature, frequency, power density, pH, sodium chloride, and sodium bicarbonate concentrations are examined as process parameters. The frequency and length of the PFAS chain were found to be vital components in the sonolytic degradation process. Degradation of all PFAS was shown to be particularly rapid at room temperature, basic pH, and a power density of 252 W/L. At a power density of 144 W/L, all of the PFAS were degraded by more than 97% in 8 h, with the exception of perfluorobutonic acid (83%) and perfluorohexanoic acid (94%). The bond dissociation energy of C-F bonds was found to be much higher than experimental sonolytic activation energies, supporting cavitation bubble as a catalyst for thermolytic destruction of PFAS compounds. Optimizing the reactor geometry has the potential to make this approach even more appealing for treating small volumes of concentrated wastes.

CFD modelling and multi-objective optimization of MHO for hydrodynamic cavitation generator using a radial basis function neural network, and NSGA-II

In this study, the design of a multi-hole orifice (MHO) commonly used in cavitation reactors, is optimized to maximize the vapor production and the turbulence intensity downstream of the MHO. The independent optimization parameters are non-homogenous distribution for peripheral holes (vertical radius, δy, and horizontal radius, δx), the diameter of the central hole, DcD, and the orifice thickness, tD. A design of experiment, a set of CFD simulations, and radial basis function neural network (RBFNN) are used to study the effect of the mentioned independent parameters on the two-objective functions. The model analysis shows that the orifice thickness is a most influential factor in vapor production, while the diameter of the central hole remarkably influences the intensity of turbulence following the MHO. The, NSGA-II algorithm is used for obtaining Pareto optimal design, which propose that an MHO with a relative orifice thickness around tD=0.15 produces both maximum vapor output and remarkable turbulence intensity. The turbulence intensity is maximized by a nonhomogeneous distribution of holes, i.e., δx=0.4 and δy=0.6. Therefore, δx and δy are responsible for collapsing bubbles due to jets mixing behind MHO. As compared to MHO with DcD=0.05, MHO with DcD=0.2 showed a pressure recovery length that was twice as long.

SIMULATION OF WATER FLOW IN A CAVITATION REACTOR

Introduction: Searching for methods to improve the efficiency of water treatment with reagents is quite important in both water conditioning and industrial wastewater purification. Among the technologies providing high efficiency and reducing resource consumption in combination with reagent methods, hydrodynamic cavitation water treatment is of particular interest. The analysis of scientific and technical data made it possible to determine the main indicators of hydrodynamic cavitation water treatment that can affect the efficiency of reagent purification. Extreme parameters occurring during intense cavitation are associated with the formation of high temperatures up to 2000°C and high pulse pressures of 100–1500 MPa in local areas of hydrodynamic systems. In such conditions, the initiation and intensification of the physical and chemical processes of water treatment are observed. Рurpose of the study: Improving the efficiency of existing traditional water purification technologies, allowing to improve its quality at the lowest cost. Methods: To study the parameters affecting water treatment efficiency and occurring with the cavitation flow of water, simulation in Ansys CFX was performed with the use of the finite volume method. The calculation was carried out with account for the turbulent nature of the flow based on the k-ε turbulence model. The cavitation process was calculated with the use of the Rayleigh-Plesset cavitation model. Results: Steam formation in the cavitation reactor promotes sufficiently complete absorption of the gaseous disinfectant by water. An increase in temperature is also considered as one of the factors increasing the efficiency of water treatment with reagents. During cavitation, water temperature increases in local micro-volumes. Thus, to intensify the process, there is no need to heat the entire volume of liquid, and, as a result, the total energy consumption for water treatment is reduced.

Performance evaluation of hydrodynamic cavitation in combination with AOPs for degradation of tannery wastewater

Tannery wastewater effluent (TWE) consists of a variety of complex structured compounds having very low biodegradability. Few attempts have been made to treat real-time TWE consisting of complex compounds and find the intermediate compounds formed during the HC+PAA+ FeSO4.7 H2O treatment system. Therefore, a pilot scale study has been conducted on an orifice-embedded hydrodynamic cavitation reactor for treating real-time TWE. Liquid chromatography-high resolution mass spectrometry (LC-HRMS) has been carried out to identify the specific compounds present in TWE before and after treatment. Response surface methodology (RSM) – Box-Behnken design (BBD) obtained maximum COD, TDS and turbidity removal efficiency of 72.36%, 94.54% and 98.89%, respectively, at cavitation time-97.5 min, inlet pressure-7.5 bar, pH-2, orifice diameter-0.5 mm, PAA dosage-17.5 g/L, and PAA /FeSO4.7 H2O-2:1 ratio. The reaction rate constant was increased from 2.455 × 10−3 to 12.75 × 10−3 min−1 when AOPs were combined with HC. The study concluded that the degradation using HC+PAA+ FeSO4.7 H2O successfully increased the biodegradability of the TWE without forming any toxic by-products.

Continuous double-step acid catalyzed esterification production of sludge palm oil using 3D-printed rotational hydrodynamic cavitation reactor

Sludge palm oil (SPO) with high free fatty acid (FFA) content was processed using a continuous and double-step esterification production process in a rotor-stator-type hydrodynamic cavitation reactor. Three-dimensional printed rotor was made of plastic filament and acted as a major element in minimizing the FFA content in SPO. To evaluate the reduced level of FFAs using both methods, five independent factors were varied: methanol content, sulphuric acid content (H2SO4), hole diameter, hole depth, and rotor speed. The first-step conditions for the esterification process included 60.8 vol% methanol content, 7.2 vol% H2SO4 content, 5.0 mm diameter of the hole, 6.1 mm depth of the hole, and 3000 rpm speed of the rotor. The initial free fatty acid content decreased from 89.16 wt% to 35.00 wt% by the predictive model, while 36.69 wt% FFA level and 94.4 vol% washed first-esterified oil yield were obtained from an actual experiment. In the second-step, 1.0 wt% FFA was achieved under the following conditions: 44.5 vol% methanol content, 3.0 vol% H2SO4 content, 4.6 mm hole diameter, 5.8 mm hole depth, and 3000 rpm rotor speed. The actual experiment produced 0.94 wt% FFA content and 93.9 vol% washed second-esterified oil yield. The entire process required an average electricity of 0.137 kWh/L to reduce the FFA level in the SPO below 1 wt%.

Dual activity cavitation reactors for increased efficacy in degradation of refractory pollutants – A case study on cephalexin degradation

The present work discloses a new form of cavitation processes using reactors of dual activity for increased efficiency. A proof of concept is established for the degradation of a refractory pollutant-cephalexin using both conventional and dual function cavitation reactors for the first time using acoustic and hydrodynamic cavitation (HC). A vortex diode as a cavitating device was employed for HC using aluminium as a non-catalytic and copper as dual function device for providing additional catalytic effect. The process intensification using hydrogen peroxide (H2O2) coupled with the dual function devices was highly effective. A negligible degradation with only HC and 81% for HC coupled with H2O2 in 60 min for Al-vortex diode compared to 100% degradation in only 5 min for the copper device clearly demonstrates the order of magnitude enhancements establishing dual function due to catalytic activity. Also, pH modification (pH 11) yields enhancement over 300% for Cu-vortex diode. The use of dual function reactors drastically reduces H2O2 dosage. The overall enhancements in the per pass degradation and cavitation yields were huge, ∼3000% and 1450% respectively, highlighting the potential of the dual function cavitation reactors in real-life applications, not just for increased efficiencies but also for significantly reduced costs.

Optimization of combustion characteristics of novel hydrodynamic cavitation based waste cooking oil biodiesel fueled CI engine

The increment in the usage of automobiles is resulting in increased greenhouse gases (GHG) emissions continuously and there is a substantial need to reduce them effectively. The present research work investigates the emission behavior of waste cooking oil biodiesel doped with CuO nanoparticles during testing in Compression Ignition (CI) engines. This investigation is based on the effective emission reduction analysis emitted by diesel fuel during experimentation on CI engines. It suggests a cost effective modification of biodiesel as a fuel prepared from waste cooking oil (WCO) by a novel hydrodynamic cavitation technique which includes the hydrodynamic cavitation reaction mixture composed of 1.28 L of methanol and 10 g KOH and 5 L of preheated WCO at 45 °C in the cavitation reactor for 40 min. These reactants are synthesized utilizing the principle of cavitation and the final manufactured esterified oil is authenticated with ASTM Standard property measurement for suitability check. In the research work, two different investigations are carried out. In the first one, WCO biodiesel-diesel blends of 0, 30, and 100% (B0, B30, B100) ratio are prepared and the emission characteristics have investigated at 1500 rpm constant speed with varying load and indicated mean effective pressure (IMEP). In the second investigation, the emission suitable blend B30 is doped with CuO nanoparticles, keeping other parameters as per the previous setup, the emission characteristics investigated for the second one. For precise results, more experimental trials are needed to achieve this decrease in the emission of harmful gases. Using an amalgamation of L9 Taguchi and response surface methodology (RSM) the maximum emission control with a minimum number of experimental trials is achieved. The first investigation includes the predefined predictors as A (blend), B (load), and C (IMEP), where blends (0 ≤ A ≤ 100%), load (0 ≤ B ≤ 12 kg), IMEP (3.5 ≤ C ≤ 7.5 bar) are controllable features. Optimization process resulted into a minimum emission of CO, CO2, and NOx by appertaining the condemnatory merger of inputs such as blend B0 (Diesel), load 12 kg, and IMEP 3.48 bar in the first investigation, which has resulted into 0.08 ppm CO, 0.6 ppm CO2 and 30 ppm NOx emission. Taguchi analysis-based second experimental investigation includes the predefined predictors as A (CuO), B (load), and C (IMEP), including nanoparticles CuO in blend B30, and the prognosticated results of optimization are 0.03 ppm CO, 0.3 ppm CO2 and 21 ppm NOx emission. In current investigation, the percentage reduction is found to be 92.3%, 94.82%, and 96% compared to the emission of diesel in CO, CO2 and NOx gases, respectively. The coefficient of determination is almost equal to 1, which reveals the chosen optimization technique is very accurate in prediction. The investigation has provided suitable minimum emission characteristics in a cost-effective way.

Recent trends in the applications of sonochemical reactors as an advanced oxidation process for the remediation of microbial hazards associated with water and wastewater: A critical review

Water is one of the major sources that spread human diseases through contamination with bacteria and other pathogenic microorganisms. This review focuses on microbial hazards as they are often present in water and wastewater and cause various human diseases. Among the currently used disinfection methods, sonochemical reactors (SCRs) that produce free radicals combined with advanced oxidation processes (AOPs) have received significant attention from the scientific community. Also, this review discussed various types of cavitation reactors, such as acoustic cavitation reactors (ACRs) utilizing ultrasonic energy (UE), which had been widely employed, involving AOPs for treating contaminated waters. Besides ACRs, hydrodynamic cavitation reactors (HCRs) also effectively destroy and deactivate microorganisms to varying degrees. Cavitation is the fundamental phenomenon responsible for initiating many sonochemical reactions in liquids. Bacterial degradation occurs mainly due to the thinning of microbial membranes, local warming, and the generation of free radicals due to cavitation. Over the years, although extensive investigations have focused on the antimicrobial effects of UE (ultrasonic energy), the primary mechanism underlying the cavitation effects in the disinfection process, inactivation of microbes, and chemical reactions involved are still poorly understood. Therefore, studies under different conditions often lead to inconsistent results. This review investigates and compares other mechanisms and performances from greener and environmentally friendly sonochemical techniques to the remediation of microbial hazards associated with water and wastewater. Finally, the energy aspects, challenges, and recommendations for future perspectives have been provided.

Degradation of Rhodamine 6G dye using a novel glass-marble packed bed reactor-based cavitation

The current research focuses on cavitation-based cavitation treatment methods based on the employment of external oxidants for the degradation of Rhodamine 6G (Rh 6G) aqueous solution. Adsorption investigations, hydrogen peroxide detection, fluid velocity, and glass-marble size assessed the reactor performance. To further intensify the process, experiments on the combined impact of two additives have been carried out at their optimum loading concentration. In addition to lowering Rh 6 G content, lentil seeds were tested for cytotoxic and genotoxic effects on meristematic cells. Preliminary investigation on the impacts of fluid velocity, marble size, pH, and initial dye concentration found that higher velocity (87.18±1.00 m/s), smaller marble size (0.6 cm), lower pH (12.5), and lower dye concentration (10 ppm) were better for degradation. Treatment methods that use hydrogen peroxide along with glass-marble packed bed reactor-based cavitation result in noticeably superior results (96.35%) than those that use hydrogen peroxide alone (11.28%). The toxicological assessment indicates Rh 6G toxicity and the ineffectiveness of the prescribed treatment. In this work, glass-marble packed bed reactor-based cavitation-based treatment approaches were shown to be a better alternative for Rh 6G degradation and enable large-capacity applications similar to orifice-venturi based hydrodynamic cavitation reactors for industrial wastewater treatment.

Degradation of magenta dye using cavitation-based transducers to glass marble: Lab to semi-pilot scale operations.

In the present work, the degradation of magenta dye has been investigated using ultrasonic (US) and ultraviolet (UV) irradiation at a laboratory scale. Additionally, the investigation was conducted at a semi-pilot scale by employing hydrodynamic cavitation and a novel air-marble cavitation reactor. Initially, optimization studies such as the effect of initial dye concentration and catalyst loading of TiO2 and MnO2 followed by the effect of combined catalyst loading (TiO2 /MnO2 ) on the extent of degradation have been studied at a capacity of 3 L. It was observed that the US irradiation results in 87.1% and 68.2% of degradation, whereas the UV irradiation results in 79.8% and 56.4% extent of degradation at 1 g/l of TiO2 and 0.8 g/l of MnO2 , respectively. The maximum degradation was 92.1% at the combined loading of 0.6 g/l (1:0.8; TiO2 :MnO2 ) using US irradiation with a capacity of 3L and 81.3% using a hydrodynamic cavitation reactor with a semi-pilot scale capacity of 7L. The chemical oxygen demand (COD) analysis also showed the highestCODremoval of 92% at a small scale using the US irradiation and 76% at a semi-pilot scale using hydrodynamic cavitation. On a small scale, the cost of a US/TiO2 + MnO2 treatment scheme is US$ 0.01/L, whereas on a semi-pilot scale using HC/TiO2 + MnO2 , the cost is US$ 0.04/L. Both of these treatment schemes offer viable pathways for degradation based on energy and economic assessments. Overall, the current work has clearly demonstrated the effectiveness of the cavitational reactor for the efficient degradation of magenta dye from lab to semi-pilot scale operation. PRACTITIONER POINTS: Small-scale dye containing wastewater treatment using ultrasound and ultraviolet irradiation Combined use of catalysts at large-scale operations with novel cavitation techniques Novel cavitation techniques studied for dye degradation. Energy efficiency and cost analysis evaluated for AOPs studies.

Recent Developments in Hydrodynamic Cavitation Reactors: Cavitation Mechanism, Reactor Design, and Applications

Hydrodynamic cavitation is considered to be a promising technology for process intensification, due to its high energy efficiency, cost-effective operation, ability to induce chemical reactions, and scale-up possibilities. In the past decade, advancements have been made in the fundamental understanding of hydrodynamic cavitation and its main variables, which provide a basis for applications of hydrodynamic cavitation in radical-induced chemical reaction processes. Here, we provide an extensive review of these research efforts, including the fundamentals of hydrodynamic cavitation, the design of cavitation reactors, cavitation-induced reaction enhancement, and relevant industrial applications. Two types of hydrodynamic cavitation reactors—namely, stationary and rotational—are compared. The design parameters of a hydrodynamic cavitation reactor and reactor performance at the laboratory and pilot scales are discussed, and recommendations are made regarding optimal operation and geometric conditions. The commercial cavitation reactors that are currently on the market are reviewed here for the first time. The unique features of hydrodynamic cavitation have been widely applied to various chemical reactions, such as oxidization reactions and wastewater treatment, and to physical processes, such as emulsion generation and component extraction. The roles of radicals and gas bubble implosion are also thoroughly discussed.

Ефективність використання сопел типу Вентурі при отриманні водних рослинних екстрактів

Technologies for obtaining extracts from plant raw materials require constant improvement due to the significant variety of species, composition and physical and chemical properties of plant raw materials. The constant increase in the volume of manufacturing products and preparations using plant extracts ma¬keit actual to search for individual approaches. Currently, cavitation technologies are considered to be one of the most effective in the treatment of gaseous, solid, and liquid media and are used in various industries. The transformation and redistribution of energy, which occur during the formation and collapse of steam-gas bubbles due to the creation of a high difference in pressure, temperature, and potential, corre¬spondd to their maximum values and contribute to increasing the active dynamic influence on the complex heterogeneous systems. During extraction, the use of hydrodynamic cavitation is allowed to effectively carry out the process of active destructtion of plant cell walls, increase the contact area between phases and intensify mass exchange processes. The design of the equip¬ment, the performance profile of the working devices, the flow parameters (absolute pressure and velocity), the critical pressure Pcav, as well as the material properties have a significant impact on the hydrodynamic conditions of the cavitation treatment. The results of research on determination the effectiveness of the use of venturi nozzles in the extraction of dry flowers of calendulaare presented in the article. The research was carried out with cavitation reactor nozzle neck with diameters of 0.006 m, 0.008 m, 0.01 m and 0.012 m. The nozzle with the minimum diameter of the neck (0.006 m) corresponds to the lowest cavitation number, which indicate the highest dispersion efficiency, but the high dispersity of the suspension makes it difficult to separate insoluble substances from the extract. In theresearch, it was established that a nozzle with diameters of 0.008 m and 0.01 mm is rational to be used. The duration of processing should be no more than 60 cycles to avoid overheating of the mixture and to prevent a critical dispersity index at which the process of filtering and separating the extract from the exhausted raw materials is significantly complicated.

Experimental and numerical investigation on the disinfection characteristics of a novel rotor-radial groove hydrodynamic cavitation reactor

Hydrodynamic cavitation was considered as a new efficient and green water treatment technology, which doesn’t produce any disinfection by-products. In the present paper, the disinfection characteristics of a novel rotor-radial groove hydrodynamic cavitation reactor were evaluated. The effects of various rotor speeds, flow rates, and initial bacterial concentrations on the removal of Escherichia coli were analyzed on the basis of experimental research and numerical simulation. The possible mechanism of hydrodynamic cavitation disinfection was explained. 93.3% disinfection rate of Escherichia coli can be obtained at 3900 rpm and 2 m3/h in 20 min for 15 L water of simulated effluent. With the increase of flow rate, the disinfection effect of the reactor was improved based on the cavitation effect and the exposure time of bacteria in the bubble collapse area (passing times). The disinfection of Escherichia coliis based on the micro jet, shock wave, and shear stress generated by hydrodynamic cavitation. The findings of the present study can provide support for the application development of hydrodynamic cavitation disinfection and the theoretical development of rotational hydrodynamic cavitation reactors.

A new multi-component marine exhaust cleaning method using combined hydrodynamic cavitation and chlorine dioxide

Simultaneous desulfurization and denitration of ship exhaust is a challenging problem. To solve the problem, we proposed a novel non-circulation cleaning method for removing nitrogen oxides (NOx) and sulfur dioxide (SO2) using combined hydrodynamic cavitation and chlorine dioxide (ClO2). The SO2 and NO removal mechanism was studied. Experiments were carried out to determine the efficiency of combined hydrodynamic cavitation and ClO2 for exhaust desulfurization and simultaneous desulfurization and denitration. The results showed that hydrodynamic cavitation could effectively desulfurize. The simultaneous desulfurization and denitration performance of combined hydrodynamic cavitation and ClO2 process was significantly better than that of hydrodynamic cavitation alone. The study found that the presence of SO2 would promote denitration and also competed with NOx for ClO2. The effects of pressure difference (ΔP) before and after the hydrodynamic cavitation reactor, NO gas flow rate (QNO), 600 mg/L ClO2 feeding rate (ηClO2), and NO initial concentration (CNOinitial) on the denitration efficiency were further studied. The results revealed that around 95.0 % of NOx removal efficiency was reached. This study could provide important theoretical support for the industrial application of this technology.

Using CFD simulations to investigate the shear stress in hydrodynamic cavitation reactors coupled with experimental validation using colony count measurements

The current work investigates the shear stress distribution in hydrodynamic cavitation reactors with two different geometries using CFD simulations. Venturi type (positive geometry) and bore (negative geometry) were used to induce cavitation. Experimental validation of the predictions from simulations was also conducted by calculating the reduction rate in the colony count of Legionella pneumophila, a pathogenic bacterial strain. Both the numerical and experimental studies revealed the significant influence of the shape of the cavitation-inducing geometry on the flow characteristics and the distribution of shear stress. The simulation data indicated high shear stress formation in the positive geometry as a venturi, with the cavitation ranges for the two reactors being far apart from each other. The experimental study also confirmed that the flow conditions in the venturi-type reactor were more favourable compared to the bore geometry, resulting in a bacterial reduction efficiency as high as 99.98%. It was clearly demonstrated that the geometry of the cavitating device plays a crucial role in deciding the shear stress and its efficacy for the desired applications as per the predictions of the simulation model validated by the experimental results.