Hydrodynamic Cavitation Device Research Articles

Removal of Diuron from Waste Waters by Hydrodynamic Cavitation

The possibility to remove herbicide diuron from waste waters without using chemicals by applying a novel hydrodynamic cavitation technology was investigated. Hydrodynamic cavitation device with a cavitator of Venturi type for waste water purification was constructed. The hydraulic characteristics of the device were determined: the dependences of flow and cavitation number on inlet pressure. The effect of cavitation number, number of passes, pH and temperature on the reduction of concentration of diuron in aqueous solution was examined. The kinetics and the kinetic model have been established and the kinetic parameters of diuron removal were calculated.

High-pressure jet-induced hydrodynamic cavitation as a pre-treatment step for avoiding cyanobacterial contamination during water purification

Due to specific physical properties, hydrodynamic cavitation (HC) is assigned to the powerful technologies for treating the biotic contamination in water including cyanobacteria. Contaminated water stream (CWS) can be cavitated directly by passing through some HC device, or indirectly when high-pressure jet stream (HPJS) is directed against its flow. Relatively small HPJS stream can thus treat a big volume of CWS in a short time or even work in continuous mode. Cyanobacteria floating in the CWS are forced to flow through the mixing cavitation zone. Within 2 h after single HC treatment, cyanobacterial cell suspensions showed disintegration of larger colonies and enhanced biomass sedimentation. Additional pre-treatment of CWS with low amounts of hydrogen peroxide (H2O2; 33, 66 and 99 μmol/L) enhanced the effect of HC and led to further inhibition of cyanobacterial photosynthesis (maximum quantum yield of photosystem II decreased by up to 60%). The number of cyanobacterial cells in the treated CWS decreased continuously over 48 and 72 h, though some cells remained alive and were able to recover photosynthetic activity. The technique proposed (direction of a HPJS against a CWS and pre-treatment with low H2O2 concentrations) provides (i) effective removal of cells from the water column, and (ii) reduced contamination by organic compounds released from the cells (especially cyanotoxins) as the cell membranes are not destroyed and the cells remain alive. This process shows potential as an effective pre-treatment step in water purification processes related to cyanobacterial contamination.

Synergistic effects of trace concentrations of hydrogen peroxide used in a novel hydrodynamic cavitation device allows for selective removal of cyanobacteria

Here, we present an improved and verified rotating hydrodynamic cavitation device (RHCD) inspired by so-called cavitation heaters. The cavitation efficiency of the device is adjustable by rotation speed and flow rate and can be modified for selective removal of cyanobacteria from water with only temporal effect on algal growth or metabolic activity. Previous hydrodynamic cavitation devices have required several cycles to achieve cyanobacterial elimination (12–200 cycles, 5–200 min of treatment), while the RHCD is capable to remove 99% of cyanobacteria after a single cycle lasting 6 s. The device efficiency at cyanobacterial removal was synergistically enhanced through the addition of trace concentrations of hydrogen peroxide (45–100 µM H2O2), levels 10–1000 times lower than those used in previous studies. The RHCD is also capable to increase temperature, an additional advantage for potential technological applications. We discuss the potential use of this device over a broad spectrum of technological processes, and especially regarding the addition of hydrogen peroxide, ozone, or ferrates, which could open new areas in advanced oxidation technologies. It could also be used as an alternative or as a complement to sonochemical, microwave-assisted or electrochemical methods in chemical engineering processes requiring treatment of large volumes of liquids.

Flow characteristics of vortex based cavitation devices

AbstractVortex based hydrodynamic cavitation (HC) devices offer various advantages over conventional linear flow devices, such as early inception, low erosion risk, and higher cavitational yield. Despite several promising applications, the key underlying flow characteristics are not yet adequately understood. This article presents results of a computational investigation into cavitation in vortex devices. Multiphase computational fluid dynamics results are presented and compared with experimental data on pressure drop over a range of flow rates. The results highlight the unique hydrodynamic characteristics of this type of device in relation to conventional linear flow reactors; cavitation inception occurs in the liquid bulk away from sold surfaces, and rapid pressure recovery rates are achieved. The models were used to simulate detailed time–pressure histories for individual vapor cavities, including turbulent fluctuations. The developed approach, models and results will provide a sound and useful basis for comprehensive multiscale modeling of vortex‐based devices for HC.

Improved flotation of PGM tailings with a high-shear hydrodynamic cavitation device

Fine liberated valuable particles are often lost to flotation tailings due to inefficient collection by air bubbles, and passivation of their surfaces by oxidation products and slimes when reclaimed from tailings dams. Extensive research covering a diverse range of technologies has been undertaken over the years to find feasible solutions to this problem, with only relatively minor success at an operations scale. A more recent and practical prospect which has already found application in the mining industry is the use of hydrodynamic cavitation devices (HCDs), causing the nucleation of ultrafine (nano) bubbles (NBs) on the surfaces of fine valuable particles, thus aiding their agglomeration and subsequent recovery by micro-bubbles (MBs) and normal sized (macro) flotation bubbles. This paper details investigations that have been undertaken on the Mach HCD reactor, using rougher, cleaner and recleaner feed samples sourced from a UG2 Platinum Group Metal (PGM) tailings operation. The results suggest that the formation of NBs and MMBs, together with enhanced cleaning of particle surfaces, were the dominant mechanisms. This not only lead to activation of valuable mineral surfaces but also depressed the recovery of gangue. The flotation kinetics were analysed using the modified Kelsall model, showing significant improvements in the maximum (fitted) recovery Rmax, together with a reduction in mass pull, for the optimum number of passes of the various feed samples through the reactor. The contributions to the increased recovery due to additional liberation of PGMs from the chromite grains and the increased gas holdup, are being investigated further.

A critical review of the current technologies in wastewater treatment plants by using hydrodynamic cavitation process: Basic principles

In the last years, hydrodynamic cavitation (HC) was increasingly used for a variety of applications in the field of wastewater treatment, ranging from biological applications (i.e. cells disruption) to chemical reactions such as oxidation of organic, bio-refractory and toxic pollutants in aqueous effluents. HC is induced in fluids by subjecting them to velocity variations due to the presence of constrictions in the flow. This process involves the formation, growth, implosion and subsequent collapse of micro-bubbles, occurring in extremely small intervals of time and releasing large magnitudes of energy over a very small location. In this paper, the vast literature on HC is critically reviewed, focusing on the basic principles behind it, in terms of process definition and analysis of governing mechanisms of both HC generation and pollutants degradation. The influence of various parameters on HC effectiveness was assessed, considering fluid properties, construction features of HC devices and technological aspects of processes. The synergetic effect of HC combined with chemicals or other techniques was discussed. An overview of the main devices used for HC generation and different existing methods to evaluate the cavitation effectiveness was provided. Knowledge buildup and optimization for such complex systems from mathematical modeling was highlighted.

A novel advanced technology for removal of phenol from wastewaters in a Ventury reactor

Phenol is a major pollutant in the waste waters coming from coal processing. Hydrodynamic cavitation presents a novel technology for phenol removal from waste waters. Hydrodynamic cavitation device with a cavitator of Ventury type for waste water purification was constructed. The hydraulic characteristic of the device were determined: the dependences of flow and cavitation number on inlet pressure. The effects of cavitation number, phenol concentration, pH, temperature, time, and quantity of added H202 on the degree of phenol reduction in the waste water was investigated. The optimal technological parameters of the investigated cavitation purification process of waste waters from phenol were determined.

Modeling hydrodynamic cavitation in venturi: influence of venturi configuration on inception and extent of cavitation

Hydrodynamic cavitation (HC) is useful for intensifying a wide variety of industrial applications including biofuel production, emulsion preparation, and wastewater treatment. Venturi is one of the most widely used devices for HC. Despite the wide spread use, the role and interactions among various design and operating parameters on generated cavitation is not yet adequately understood. This article presents results of computational investigation into the cavitation characteristics of different venturi designs over a range of operating conditions. Influence of the key geometric parameters such as the length of venturi throat and diffuser angle on the inception and extent of cavitation is discussed quantitatively. Formulation and solution of multiphase computational fluid dynamics (CFD) models are presented. Appropriate turbulence and cavitation models are selected and solved using a commercial CFD code. Care was taken to eliminate the influence of numerical parameters like mesh density, discretization scheme, and convergence criteria. The computational model was validated by comparing simulated results with three published data sets. The simulated results in terms of velocity and pressure gradients, vapor volume fractions and turbulence quantities, and so on, are critically analyzed and discussed. Diffuser angle was found to have a significant influence on cavitation inception and evolution. The length of the venturi throat has relatively less impact on cavitation inception and evolution compared to the diffuser angle. The models and simulated flow field were used to simulate detailed time–pressure histories for individual vapor cavities, including turbulent fluctuations. This in turn can be used to simulate cavity collapse and overall performance of HC device as a reactor. The presented results offer useful guidance to the designer of HC devices, identifying key operating and design parameters that can be manipulated to achieve the desired level of cavitational activity. The presented approach and results also offer a useful means to compare and to evaluate different designs of cavitation devices and operating parameters. © 2018 American Institute of Chemical Engineers AIChE J, 65: 421–433, 2019

Experimental Study of Pathogenic Microorganisms Inactivated by Venturi-Type Hydrodynamic Cavitation with Different Throat Lengths

Based on self-developed Venturi-type hydrodynamic cavitation device with different throat length-radius ratios L/R in Hydraulics Laboratory at Zhejiang University of Technology in China, 4 throat length-radius ratios L/R=10, 30, 60 and 100, and 4 raw water percentages V0/V=25%, 50%, 75%, and 100% were considered, Escherichia coli and total colony count were selected for indicator bacteria, effects of throat length-radius ratio, throat velocity, cavitation time, raw water percentage and cavitation number on inactivating pathogenic microorganism in raw water by hydrodynamic cavitation were experimentally studied. The results showed cavitation damage of cells of pathogenic microorganisms occurred by microjets and shock waves due to cavitation bubble collapse. The lower the flow cavitation number, the higher the killing rate of E. coli and total colony count. When flow velocity was lower or raw water percentage was higher, killing rate gradually increased with increase in throat length-radius ratio; when flow velocity was higher or raw water percentage was lower, killing rate was almost independent of throat length-radius ratio. Inactivated effect of pathogenic microorganisms can be further enhanced by increasing throat velocity or prolonging cavitation time. Hydrodynamic cavitation is a novel disinfection technique for drinking water without disinfection byproducts (DBPs) and no need to add disinfectant.

Continuous biosynthesis of silver nanoparticles in a hydrodynamic cavitation device and modeling of the process by numerical simulation strategy

Silver nanoparticles (AgNPs) with size distribution 7.1 ± 1.2 nm are continuously biosynthesized with Cacumen platycladi (CP) leaf extract (0.3 g/L) at room temperature (30 °C) in the hydrodynamic cavitation device. The products are characterized by UV-Vis absorption spectra, XRD, TEM, and HRTEM, confirming that AgNPs with uniform distribution are successfully synthesized. CFD and population balance equation (PBE) coupled models are built to simulate the AgNP formation process and calculate the corresponding particle size distribution numerically. The coupled model is validated accurately and effectively with experiment in simulating of AgNP formation and predicting the particle size distribution (PSD) in the hydrodynamic cavitation device.

Treatment of Solvent-Contaminated Water Using Vortex-Based Cavitation: Influence of Operating Pressure Drop, Temperature, Aeration, and Reactor Scale

Hydrodynamic cavitation is being increasingly pursued for the development of an intensified and compact wastewater-treatment process. Experimental data on the degradation of water contaminated with three commonly used solvents (acetone; ethyl acetate, EA; and isopropyl alcohol, IPA) using vortex-based cavitation devices are presented. The influence of operating flow or pressure drop across cavitation devices (150 to 300 kPa), operating temperatures (20 to 45 °C), concentrations of pollutant (1000 to 50 000 ppm), and scales of the cavitation reactor (with a scaling-up factor of 4, maintaining the geometric similarity) has been reported. A new reaction-engineering model based on the number of passes through the cavitation device was developed to interpret degradation behavior. The model provides a convenient way to estimate the per-pass degradation factor from batch experiments and allows its extension to continuous processes and to more-sophisticated models for estimating the generation of hydroxyl radicals. The model showed excellent agreement with experimental data. The per-pass degradation factor exhibited a maxima with respect to pressure drop (200–250 kPa) across cavitation devices. Aeration was found to improve degradation performance up to 1 vvm ([L/min]gas/Lliquid]). The initial concentrations of acetone (1000 to 50 000 ppm) and IPA (1000 to 22 000 ppm) were found to have a negligible effect on degradation performance. The per-pass degradation factor for EA was 1.5 and 4 times that of acetone and IPA, respectively. The effect of two scales (nominal capacities of the small- and large-scale devices used were 0.3 and 1.2 m3/h, respectively) was investigated for the first time, and it was found that the per-pass degradation factor decreased with scale. The presented model and experimental data provide new insights into the application of hydrodynamic cavitation for wastewater treatment and provide a basis for further work on the scaling-up of hydrodynamic cavitation devices. The results will be useful to researchers as well as practicing engineers interested in harnessing hydrodynamic cavitation for water treatment.

Modelling of hydrodynamic cavitation with orifice: Influence of different orifice designs

Hydrodynamic cavitation (HC) may be harnessed to intensify a range of industrial processes, and orifice devices are one of the most widely used for HC. Despite the wide spread use, the influence of various design and operating parameters on generated cavitation is not yet adequately understood. This paper presents results of computational investigation into cavitation in different orifice designs over a range of operating conditions. Key geometric parameters like orifice thickness, hole inlet sharpness and wall angle on the cavitation behaviour is discussed quantitatively. Formulation and numerical solution of multiphase computational fluid dynamics (CFD) models are presented. The simulated results in terms of velocity and pressure gradients, vapour volume fractions and turbulence quantities etc. are critically analysed and discussed. Orifice thickness was found to significantly influence cavitation behaviour, with the pressure ratio required to initiate cavitation found to vary by a factor of 10 for orifice thickness to diameter (l/d) ratios in the range of 0–5. Inlet radius similarly has a pronounced effect on cavitational activity. The results offer useful guidance to the designer of HC devices, identifying key parameters that can be manipulated to achieve the desired level of cavitational activity at optimised hydrodynamic efficiencies. The models can be used to simulate detailed time-pressure histories for individual vapour cavities, including turbulent fluctuations. This in turn can be used to simulate cavity collapse and overall performance of HC device. The presented approach and results offer a useful means to compare and evaluate different cavitation device designs and operating parameters.

Killing rate of colony count by hydrodynamic cavitation due to square multi-orifice plates

Currently,in water supply engineering, the conventional technique of disinfection by chlorination is employed to kill pathogenic microorganisms in raw water. However, chlorine reacts with organic compounds in water and generates disinfection byproducts (DBPs), such as trihalomethanes (THMs), haloacetic acids (HAAs) etc. These byproducts are of carcinogenic, teratogenic and mutagenic effects, which seriously threaten human health. Hydrodynamic cavitation is a novel technique of drinking water disinfection without DBPs. Effects of orifice size, orifice number and orifice layout of multi-orifice plate, cavitation number, cavitation time and orifice velocity on killing pathogenic microorganisms by cavitation were investigated experimentally in a self-developed square multi-orifice plate-type hydrodynamic cavitation device. The experimental results showed that cavitation effects increased with decrease in orifice size and increase in orifice number, cavitation time and orifice velocity. Along with lowering in cavitation number, there was an increase in Reynolds shear stress,thus enhancing the killing rate of pathogenic microorganism in raw water. In addition, the killing rate by staggered orifice layout was greater than that by checkerboard-type orifice layout.

Hydrodynamics features in cavitation devices under tangent medium input

Theoretically analysed design features of the working section of a hydrodynamic cavitation device with swirling input. Using the numerical methods of SolidWorks software and the Flow simulation module, fluid flow modeling was performed to describe similar processes. The comparison of the results of visual and experimental studies has been carried out. Visual observations indicate that the life cycle of vapor-gas bubbles and cavities in the design under study can be divided into several periods, in particular the formation of vapor-gas bubbles, their growth, generation of cavities, their volume increase, transformation and destruction. The influence of input and output hydrodynamic and technological parameters of the flow and design features on the character of the cavitation area and the form of cavitation were studied. According to the results of theoretical and experimental research, rational mode of operation of the cavitation device is proposed.

Increase of acenaphthene content in creosote oil by hydrodynamic cavitation

A hydrodynamic cavitation device was applied to increase the acenaphthene amount in creosote oil. In the presence of FeSO4 and H2O as an inducer and initiator, respectively, effects of H2O amount, Fe2+ loading and pH of FeSO4 solution were investigated by mean of the orthogonal experiment method, and effects of cavitating reaction temperature as well as the height of cavitator immersing in the feedstock by single factor method. The result indicated that the maximum increase was 7.06 percentage points under the optimum conditions as follows: H2O amount 17.5% by the volume of feedstock, Fe2+ loading 0.3% by weight of feedstock, pH of FeSO4 solution 1, the terminal temperature T of cavitating reaction 75°C, and the immersing height of cavitator H 105mm. Based on the change trend of components in creosote oil the reaction mechanism was derived, and the validity of derivation process was confirmed by the material balance.

Degradation of reactive orange 4 dye using hydrodynamic cavitation based hybrid techniques

In the present work, degradation of reactive orange 4 dye (RO4) has been investigated using hydrodynamic cavitation (HC) and in combination with other AOP’s. In the hybrid techniques, combination of hydrodynamic cavitation and other oxidizing agents such as H2O2 and ozone have been used to get the enhanced degradation efficiency through HC device. The hydrodynamic cavitation was first optimized in terms of different operating parameters such as operating inlet pressure, cavitation number and pH of the operating medium to get the maximum degradation of RO4. Following the optimization of HC parameters, the degradation of RO4 was carried out using the combination of HC with H2O2 and ozone. It has been found that the efficiency of the HC can be improved significantly by combining it with H2O2 and ozone. The mineralization rate of RO4 increases considerably with 14.67% mineralization taking place using HC alone increases to 31.90% by combining it with H2O2 and further increases to 76.25% through the combination of HC and ozone. The synergetic coefficient of greater than one for the hybrid processes of HC+H2O2 and HC+Ozone has suggested that the combination of HC with other oxidizing agents is better than the individual processes for the degradation of dye effluent containing RO4. The combination of HC with ozone proves to be the most energy efficient method for the degradation of RO4 as compared to HC alone and the hybrid process of HC and H2O2.

Experimental Study of the Porous Plate Hydrodynamic Cavitation Device and Removal the Algae in Water

Design a practical and effective hydrodynamic cavitation experimental apparatus, the establishment of cavitation radical scavenging method, the use of methylene blue to study the relationship of the hydroxyl radical production and cavitation cavitation intensity, the study of the various factors of cavitation radical production, and to explore optimal cavitation strengthen the conditions. Hydrodynamic cavitation kill algae has some effect, there will be varying degrees of decline in the concentration of algae. The hydrodynamic cavitation algae suppression and damaging effects.

Removal of blue-green algae using the hybrid method of hydrodynamic cavitation and ozonation

A suspension of Microcystis aeruginosa (30μgL−1chlorophyll a) was circulated in a hydrodynamic cavitation device and ozone was introduced at the suction side of the pump. The removal of algae over 10min using hydrodynamic cavitation alone and ozone alone is less than 15% and 35%, respectively. The destruction of algae rises significantly from 24% in the absence of the orifice to 91% with the optimized orifice on 5min of processing using hydrodynamic cavitation along with ozone (HC/O3) and the utilization of ozone increases from 32% to 61%. Interestingly, the suction process is more effective than the extrusion method (positive pressure) and the optimal bulk temperature for algal elimination was found to be 20°C. Increasing the input concentration of ozone is favorable for the removal of algae but leads to a greater loss of ozone and a decrease in the utilization of ozone. Under the optimal conditions, the algal cells and chlorophyll a are completely destroyed in 10min by use of the hybrid method.

Kidney Stone Erosion by Micro Scale Hydrodynamic Cavitation and Consequent Kidney Stone Treatment

The objective of this study is to reveal the potential of micro scale hydrodynamic bubbly cavitation for the use of kidney stone treatment. Hydrodynamically generated cavitating bubbles were targeted to the surfaces of 18 kidney stone samples made of calcium oxalate, and their destructive effects were exploited in order to remove kidney stones in in vitro experiments. Phosphate buffered saline (PBS) solution was used as the working fluid under bubbly cavitating conditions in a 0.75 cm long micro probe of 147 μm inner diameter at 9790 kPa pressure. The surface of calcium oxalate type kidney stones were exposed to bubbly cavitation at room temperature for 5 to 30 min. The eroded kidney stones were visually analyzed with a high speed CCD camera and using SEM (scanning electron microscopy) techniques. The experiments showed that at a cavitation number of 0.017, hydrodynamic bubbly cavitation device could successfully erode stones with an erosion rate of 0.31 mg/min. It was also observed that the targeted application of the erosion with micro scale hydrodynamic cavitation may even cause the fracture of the kidney stones within a short time of 30 min. The proposed treatment method has proven to be an efficient instrument for destroying kidney stones.

Cavitation milling of natural cellulose to nanofibrils

Cavitation holds the promise of a new and exciting approach to fabricate both top down and bottom up nanostructures. Cavitation bubbles are created when a liquid boils under less than atmospheric pressure. The collapse process occurs supersonically and generates a host of physical and chemical effects. We have made an attempt to fabricate natural cellulose material using hydrodynamic as well as acoustic cavitation. The cellulose material having initial size of 63 micron was used for the experiments. 1% (w/v) slurry of cellulose sample was circulated through the hydrodynamic cavitation device or devices (orifice) for 6 h. The average velocity of the fluid through the device was 10.81 m/s while average pressure applied was 7.8 kg/cm 2. Cavitation number was found to be 2.61. The average particle size obtained after treatment was 1.36 micron. This hydrodynamically processed sample was sonicated for 1 h 50 min. The average size of ultrasonically processed particles was found to be 301 nm. Further, the cellulose particles were characterized with X-ray diffraction (XRD) and differential scanning calorimetry (DSC) to see the effect of cavitation on crystallinity ( X c) as well as on melting temperature ( T m). Cellulose structures consist of amorphous as well as crystalline regions. The initial raw sample was 86.56% crystalline but due to the effect of cavitation, the crystallinity reduced to 37.76%. Also the melting temperature ( T m) was found to be reduced from 101.78 °C of the original to 60.13 °C of the processed sample. SEM images for the cellulose (processed and unprocessed) shows the status and fiber–fiber alignment and its orientation with each other. Finally cavitation has proved to be very efficient tool for reduction in size from millimeter to nano scale for highly crystalline materials.