Hydrodynamic Cavitation Reactor Research Articles

Study on cavitation and pulsation characteristics of a novel rotor-radial groove hydrodynamic cavitation reactor

Abstract Hydrodynamic cavitation is widely used in many fields such as water treatment, impact rock breaking, and food preparation. The performance of hydrodynamic cavitation is closely related to its internal flow field. In the present study, cavitation flow field was analyzed by computational fluid dynamics in the reactor. The cavitation performance of the rotor is evaluated under different operating conditions. The time frequency distribution of pressure pulsation is studied. The pressure increases at the connection point between the local low-pressure area and the mainstream low-pressure area. Cavitation bubbles collapsed at the tail end of the cavity to form a local void area. The blade frequency amplitude of pressure pulsation shows the significant periodic change. The blade frequency amplitude decreases along the flow direction. The effect of the fluid outlet led to the increase in the second-order harmonic frequency amplitude. The research results could provide theoretical support for the research of cavitation mechanism of cavitation equipment.

A hydrodynamic cavitation prototype reactor evaluation for decreasing cephalexin concentration in aqueous solution

A prototype of a hydrodynamic cavitation reactor was evaluated to determine the effectiveness of this system on the percentage decrease of cephalexin concentration present in an aqueous solution prepared with ultrapure water. The process variables or factors were pH [5 and 9], number of holes in the cavitation plate [5 and 7] and reaction time (30 min and 60 min). The results indicate that the percentage removal of Cephalexin (CFX) and total organic carbon (TOC) depends on the variables studied and the interaction between them. The highest yields were achieved at pH 5, 5 holes in the cavitation plate and 60 min of reaction reaching values of 24.16 % for CFX and 16.8 % for TOC. It was determined that, for the lowest number of holes in the cavitation plate and acid pH, the phenomenon that guides the process is the hydrodynamic cavitation, when increasing the number of holes and therefore decreasing the intensity of cavitation, the pH becomes more relevant and has incidence on the performance of the analyzed process. On the other hand, it was determined that, also in reaction times of 30 min, removal values very close to the maximum values obtained are achieved. The process can be intensified by the simultaneous application of other advanced oxidation processes to increase the effectiveness.

Modelling of chemical kinetics in the presence of hydrodynamic cavitation for wastewater treatment applications

The reaction rate of hydroxyl radicals with organic pollutants is about 108−1011 /mol-s, can degrade a wide range of pollutants. Intense bubble collapse during hydrodynamic cavitation can produce hydroxyl radicals, making it suitable for wastewater treatment. The current study introduces a numerical method of predicting the performance of a hydrodynamic cavitation reactor. Unlike most literature that considers cavitation volume as an indicator of effectiveness of hydrodynamic cavitation, the present approach considers local pressure variation, cavitation volume fluctuation, radical production and their inter-relations. The findings show that though an initial increase in the extent of cavitation, marked by a rise in cavity volume, leads to higher OH. radical production, the radical generation declines below an optimal cavitation number. The downstream recovery pressure also influences radical production. This numerical methodology, providing complete picture of radical production and its locations, will be very helpful for designing a new and more efficient cavitation reactor.

Preparation of water-soluble cadmium sulfide quantum dots with narrow small-size distribution by controlling hydrodynamic cavitation device parameters

With the increasingly broad application of quantum dots in many fields, how to further improve the performance of quantum dots in various aspects has become an urgent problem to be solved. In this study, hydrodynamic cavitation (HC) technology was applied for the first time in the preparation of quantum dots. Specifically, cadmium sulfide quantum dots (CdS QDs) with small particle size, narrow distribution, high concentration and large Stokes shift are prepared. Firstly, CdS precipitation was obtained in an aqueous solvent, using cadmium nitrate tetrahydrate (Cd(NO3)2·4H2O) and sodium sulfide nonahydrate (Na2S·9H2O) as Cd and S sources, respectively. Subsequently, CdS QDs were formed from top to bottom through hydrodynamic cavitation reactor, which generates high temperature, high pressure, high-speed jets, shear forces, and shock waves. In summary, the intrinsic advantages of HC technology offer a new opportunity for manufacturing large-scale quantum dots with superb performance.

Numerical simulation of cavitation-vortex interaction mechanism in an advanced rotational hydrodynamic cavitation reactor

Hydrodynamic cavitation (HC), a promising technology for enhancing processes, has shown distinct effectiveness and versatility in various chemical and environmental applications. The recently developed advanced rotational hydrodynamic cavitation reactors (ARHCRs), employing cavitation generation units (CGUs) to induce cavitation, have demonstrated greater suitability for industrial-scale applications than conventional devices. However, the intricate interplay between vortex and cavitation, along with its spatial-temporal evolution in the complex flow field of ARHCRs, remains inadequately elucidated. This study investigated the interaction mechanism between cavitation and vortex in a representative interaction-type ARHCR for the first time using the “simplified flow field strategy” and the Q-criterion. The findings reveal that the flow instability caused by CGUs leads to intricate helical and vortex flows, subsequently giving rise to both sheet and vortex cavitation. Subsequently, utilizing the Q-criterion, the vortex structures are identified to be concentrated inside and at CGU edges with evolution process of mergence and separation. These vortex structures directly influence the shape and dimensions of cavities, establishing a complex interaction with cavitation. Lastly, the vorticity transport equation analysis uncovered that the stretching and dilatation terms dominate the vorticity transport process. Simultaneously, the baroclinic term focuses on the vapor-liquid interface, characterized by significant alterations in density and pressure gradients. These findings contribute to a better comprehension of the cavitation-vortex interaction in ARHCRs.

Degradation of Procion brilliant yellow H-E6G using ultrasonic and hydrodynamic cavitation combined with oxidants with demonstration at pilot scale.

The current study focuses on the degradation of Procion brilliant yellow H-E6G, an azo dye, using ultrasonic and hydrodynamic cavitation (HC), evaluating the impact of various parameters on the extent of degradation. The use of only ultrasound showed less oxidation capacity as indicated by only 19.1% degradation at an optimized power of 140 W, pH of 2.5, temperature of 40°C, and initial dye concentration of 15 ppm. The effectiveness of hybrid approaches involving US + H2 O2 , US + Fenton, and US + H2 O2 + potassium persulfate (KPS) was subsequently evaluated under optimized conditions. A notable enhancement in decolorization extent was observed for combined operations, including US + H2 O2 , US + Fenton, and US + H2 O2 + KPS (dual oxidant scheme) with the actual decolorization extents as 80.6%, 85%, and 92.2% respectively. An optimized scheme of US + H2 O2 + KPS was also utilized to decolorize the dye at a pilot scale using a US flow cell and also an HC reactor that yielded 91.8% and 88% reductions in initial concentration. The dye decolorization was elucidated to follow first-order kinetics for all the individual and combination approaches. The obtained values of the rate constants were also utilized for the evaluation of the synergistic index. A toxicity analysis was also performed on the dye, both before and following treatment, utilizing two bacterial strains. A comparative analysis of various treatment approaches has been presented focusing on factors such as cavitational yield, operational expenses, and energy requirements. The study elucidated that the combination of US + H2 O2 + KPS effectively removes Procion brilliant yellow H-E6G giving 92.2% as the maximum degradation at an operating cost of 0.1862 $/L. PRACTITIONER POINTS: First depiction of cavitative degradation of Procion brilliant yellow H-E6G Optimizing the equipment operating parameters and chemical oxidants Demonstration of optimized treatment scheme at pilot scale Evaluation of various approaches based on synergy and costs of treatment US + H2 O2 + KPS is the best approach for dye degradation.

Numerical investigation of effect of geometric parameters on performance of rotational hydrodynamic cavitation reactor

The objective of this paper is to discuss the influence of geometric parameters on the performance of the rotational hydrodynamic cavitation reactor (RHCR) using numerical method. The novel RHCR is implemented by modifying a centrifugal impeller into a new one using the annular slit constriction (ASC) with circumferentially distributed blind holes. The cavitation intensity and cavitation generation rate are selected to evaluate the cavitation performance, the head is used to assess conveying performance, and the entropy generation theory is used to evaluate the energy loss in the impeller. The effect of the axial width, radial length and radial position of the ASC on the cavitating flow of the RHCR is investigated by CFD method. The results indicate that three patterns of cavitation are induced in the RHCR, including separation cavitation, vortex cavitation and shear cavitation. The axial width, radial length and radial position of the ASC are the important geometric parameter that affect the performance of the RHCR. A small width is superior to a large width in terms of cavitation performance, although the conveying performance suffers as a result. The energy loss in the impeller initially increases and then decreases as the width decreases. Both a reduction in radial length and radial position leads to higher cavitation and conveying capacity, accompanying slight increase in energy loss. Compared to the original model, the RHCR with an axial width of 3 mm, a radial length of 17 mm, and a radial position of 0.541 achieves the highest performance.

An Application of Orifice Hydrodynamic Cavitation Reactor for Tertiary Treatment of Wastewater Treatment Plant Effluents

An Application of Orifice Hydrodynamic Cavitation Reactor for Tertiary Treatment of Wastewater Treatment Plant Effluents

Application of combined hydrodynamic cavitation and Fenton reagent for COD reduction of cellulosic fiber industry effluents

The present work demonstrates the implementation of combined approach of hydrodynamic cavitation reactor and Fenton oxidation process for the treatment of three cellulosic fiber (CF) industry effluent streams using pilot scale reactor with operation at 500 L developed at an industrial site. In order to assess the techno-economic viability of the combined hydrodynamic cavitation (HC) and Fenton oxidation process, various sets of experimental runs were carried out. Effect of type of treatment approach, one step and stepwise addition of oxidants, number of cavitation passes, and finally the type of effluent varying in terms of initial chemical oxygen demand (COD) on the efficacy of treatment were studied. Based on the results, HC + Fenton oxidation scheme was demonstrated to be a viable option for the treatment of CF industry effluent streams. HC + Fenton treatment rapidly reduced COD, achieving almost 90 % reduction in just 10 min, highlighting its efficiency in industrial wastewater treatment. The treatment achieved substantial reduction in residual COD levels with actual value as up to 1000 mg/L COD in effluent-I, up to 150 mg/L COD in effluent-II, and up to 100 mg/L COD in effluent-III. The study also explored the operating cost expenditure (Opex) of the proposed system required to demonstrate it at a commercial level, including the cost of chemicals and electricity. The COD reduction cost evaluated were INR 140–230/kg COD depending on the effluent. The main highlight of the article is the practical demonstration at the manufacturing unit including the operating cost calculations.

Study on DeNOx of NaClO2 in simulated seawater solution enhanced by hydrodynamic cavitation

Ship exhaust causes significant air pollution, and NOx is one of the most challenging pollutants to remove. In this study, we propose a novel method for denitrification (DeNOx) using NaClO2-simulated seawater solution enhanced by hydrodynamic cavitation. We investigate the impact of initial solution pH, temperature, NaClO2 concentration, and the inlet pressure of the hydrodynamic cavitation reactor on DeNOx efficiency. The results indicate that under optimal conditions, a 100 % DeNOx efficiency can be achieved with a NaClO2 concentration of 0.1 mmol/L. Cavitation enhances mass transfer by generating microjets and increasing the gas–liquid contact area. The oxidation of NO and NO2 by hydroxyl radicals and chlorine oxygen radicals produced through cavitation could potentially enhance NOx removal efficiency. The presence of dissolved salts in simulated seawater might boost cavitation activity by reducing vapour pressure and increasing interfacial tension, leading to the more robust collapse of cavitation bubbles and thereby reinforcing cavitation effects. In addition, the multiple reactive inorganic chlorinated radicals (Cl, HClO / ClOH·-, Cl2·-) formed in simulated seawater due to the presence of Cl- might also play an essential role in DeNOx. This study demonstrated that the DeNOx by NaClO2 in simulated seawater enhanced by hydrodynamic cavitation was a promising option for NOx removal, especially for ocean-going vessels.

Hydrodynamic Cavitation Reactor for Efficient Biodiesel Production. A Review

Biodiesel emerges as a viable option to replace fossil fuels, but the traditional process for the production of biodiesel requires a large energy expenditure, since transesterification has a slow conversion due to the immiscibility of alcohol and oil. On the other hand, with the hydrodynamic cavitation method, a shorter conversion time can be achieved with a high yield; however, there are few studies related to this method. Therefore, the objective of this article is to analyze information from different scientific publications to compare and visualize the parameters used to obtain biodiesel by means of a hydrodynamic cavitation reactor. For this reason, a bibliometric analysis and a systematic review based on the PRISMA method were carried out. In this sense, the relevant articles were selected from the Web of Science, Scopus and Google Scholar databases published between January 2018 and July 2023.Finally, the values of biodiesel yield efficiency were obtained by analyzing the different operating parameters and the different feedstock sources for its elaboration in the hydrodynamic cavitation reactors and comparing their results with international standards. American Society for Testing and Materials (ASTM) D6751 y European Committee for Standardization(EN)14214. It is concluded that hydrodynamic cavitation produces biodiesel that meets international standards and that the highest yields in biodiesel production in most studies have temperature ranges between 50 to 65°C, alcohol: oil molar ratio of 6:1, and methanol is the most used in tranasesterification.

Detergent Dissolution Intensification via Energy-Efficient Hydrodynamic Cavitation Reactors.

In this study, we explored the potential of hydrodynamic cavitation (HC) for use in dissolution of liquid and powder detergents. For this, microfluidic and polyether ether ketone (PEEK) tube HC reactors with different configurations were employed, and the results from the reactors were compared with a magnetic stirrer, as well as a tergotometer. According to our results PEEK tube HC reactors present the best performance for dissolution of liquid and powder detergents. In the case of liquid detergent, for the same level of initial concentration and comparable final dissolution, the PEEK tube consumed 16.7 and 70% of the energy and time of a tergotometer and 16.7 and 14.8% of that of a magnetic stirrer, respectively. In the case of powder detergent, the PEEK tube used 12% less power than a tergotometer and 81.2% less power than a magnetic stirrer. Additionally, the time required to dissolve the detergent was reduced significantly from 1200 s in the tergotometer and 1800 s in the magnetic stirrer to just 50 s in the PEEK tube. These results suggest that HC could significantly improve the dissolution rate of liquid and powder detergents and energy consumption in washing machines.

Effect of the arrangement of cavitation generation unit on the performance of an advanced rotational hydrodynamic cavitation reactor

Hydrodynamic cavitation (HC) is widely considered a promising process intensification technology. The novel advanced rotational hydrodynamic cavitation reactors (ARHCRs), with considerably higher performance compared with traditional devices, have gained increasing attention of academic and industrial communities. The cavitation generation unit (CGU), located on the rotor and/or stator of an ARHCR, is utilized to generate cavitation and consequently, its geometrical structure is vital for the performance. The present work studied, for the first time, the effect of the arrangement of CGU on the performance of a representative ARHCR by employing computational fluid dynamics based on the “simplified flow field” strategy. The effect of CGU arrangement, which was neglected in the past, was evaluated: radial offset distance (c), intersection angle (ω), number of rows (N), circumferential offset angle (γ), and radial spacing (r). The results indicate that the CGU, with an arrangement of a low ω and moderate c, N, γ, and r, performed the highest cavitation efficiency. The corresponding reasons were analyzed by combining the flow field and cavitation pattern. Moreover, the results also exposed a weakness of the “simplified flow field” strategy which may induce the unfavorable “sidewall effect” and cause false high-pressure region. The findings of this work may provide a reference value to the design of ARHCRs.

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.

Intensification of biodiesel production by hydrodynamic cavitation: A critical review

Biodiesel, with its nature of clean, biodegradability, and renewability, is an ideal substitute for fossil diesel. This critical review focuses on the advances in process intensification of biodiesel production by the emerging hydrodynamic cavitation (HC) technology. The recent progress in HC reactors and HC-assisted biodiesel production are summarized and discussed. Several key operating factors (i.e., reactor structure, cavitation intensity, temperature, molar ratio of alcohol to oil, catalyst, and duration) and the economic feasibility are analyzed. It is found that HC can effectively enhance acid- and alkali-catalyzed production processes by using various edible and non-edible oils (e.g., waste cooking oil) as feedstocks, and have economic practicability for industrialization. HC can achieve as high as over 99% yields in a short time, and the quality of the high-purity products meets EN 14214 and ASTM D6751 standards. Although the process simulation and life cycle cost analysis (LCCA) validated that the economics of HC process is far superior to that of conventional mechanical stirring at large scales, the experimental research at pilot or industrial scales is absent, and the amplification effect of both the reactor and process is unclear. Moreover, the investigations on the cavitation flow mechanism, structural optimization and design of HCRs, and feasibility (e.g., life cycle analysis (LCA), LCCA, and LCA-LCCA), have to be focused on in the future. At last, the strengths, weaknesses, opportunities, and threats (SWOT) of the HC process are evaluated by a SWOT matrix, which may hopefully provide some inspiration for the future development of this novel technology.

The divergent angle of cavitational devices influences melanoidin degradation. A new look through experimental and computational analysis

In the present work, the influence of the divergent section angle of hydrodynamic cavitation (HC) devices on melanoidin degradation was investigated. The HC reactor was operated alone and in combination with an oxidant at four concentrations of H2O2: 0.9, 2.8, 4.7, 6.6 g L−1. Five Venturi devices (with divergent angles of 4°, 8°, 11°, 14°, and 90°) were made and analyzed at five operating pressures (150, 300, 440, 600, 760 kPa) for a period of 30 min. ANOVA and Fisher's LSD method were used to define the best angle and the best operating pressure for melanoidin degradation. The highest efficiency of melanoidin degradation (14.32 %) was obtained with an angle of 11° and a pressure of 600 kPa. Computational Fluid Dynamics (CFD) simulations were performed to study the influence of the divergent angle on the flow parameters. They showed that at smaller angles (4° and 8°) there was an excess growth of cavities, increasing the chance of coalescence of cavities and reducing the intensity of collapse. On the other hand, at a very high angle (90°), the cavities collapsed before growing, releasing less energy at the time of implosion. The degradation efficiency increased to 60.84 % when 2.8 g L−1 of H2O2 was applied to the HC reactor, at pH 2.5. Higher concentrations of H2O2 reduced the degradation efficiency, indicating a “scavenging” effect in combined systems (HC + H2O2) due to the generation of unreactive radicals. The present study demonstrated that the combination of HC + H2O2 is a promising alternative for melanoidin degradation, with the divergent angle of the device being an important parameter of this treatment process.

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%.