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The aim of this work is to perform design and optimization of a cavitating device based on CFD simulation. A set of operational and geometrical parameters such as convergence angle, divergence angle, length of throat, and inlet pressure that can affect the hydrodynamic cavitation phenomenon generating in a Venturi are evaluated through CFD simulati...
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... order to evaluate the performance of Venturi, cavitation length is compared to experimental section. Pressure contour of the optimized Venturi in experimental conditions i.e. optimum inlet pressure of 5 bar and temperature of 36℃ is shown in Fig. 6. The pressure contour has been matched with imaging evidence of cavitation zone forming in Venturi. Fig. 7 shows image of cavitation zone in the downstream of ...
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... In order to describe the hydrodynamic characteristics of different Venturi designs, the pressure-based transient mixture multiphase approach was applied, which solved one set of Unsteady Reynolds Averaged Navier-Stokes equations (URNAS) using the finite volume method. For the turbulent characteristics within the tube, the standard k-ε turbulence model is used [49][50][51]. The velocity at the water inlet and the pressure at the air inlet and mixture outlet were specified as boundary conditions. ...
... Several geometrical parameters were also comprehensively estimated in the previous works, including diverging angle [33,[37][38][39], converging angle [38], throat diameter [39] and throat length [33,[38][39][40]. Moreover, Abbasi et al. [41] and Abbas-Shiroodi et al. [42] found out the optimal geometric configuration by multi-objective optimization. Furthermore, few researchers also proposed innovative modifications of Venturi structure for the further improvement of Venturis. ...
As one of the advanced oxidation processes, hydrodynamic cavitation (HC) has become a promising technology for treating industrial effluents by various cavitation devices due to the advantages of cost-effectiveness in operation, higher energy efficiencies, and large-scale operation. In this study, the effect of a distinctive division baffle on the performance of a circular Venturi is proposed focusing on the enhancement of cavitation intensity and reaction area by utilizing computational fluid dynamics. Three geometrical parameters of the distinctive division baffle, including divergent angle (β 2), convergent angle (α 2), and throat diameter (d 2), were investigated , after a well validation of the numerical method with a previous experiment. It was found that the β 2 and d 2 provided relatively more significant impact on cavitation intensification. Through the comprehensive evaluation of the selected three parameters, the most appropriate geometrical configuration of the novel Venturi was determined as a divergent angle β 2 of 6 • , a convergent angle α 2 of 16 • , and a throat diameter d 2 of 2.25 mm. Furthermore, the finally recommended design, significantly intensifying the cavitating process, has been tested at different pressure ratios and cavitating zone of recommended design is always much larger than original model. The recommended design achieved a vapor volume increasing rate of 102.3 %, 41 % and 57.5 % at PR = 2, 4 and 6. In conclusion, the novel strategy of Venturi with distinctive division baffle may provide inspiration and reference to the future research and industrial application of HC technology.
... In 2022, the influence of wall roughness on the cavitation phenomena in a venturi reactor was studied using CFD approach by Dutta and Nirmalkar. 14 Geometrical parameters of a venturi tube (length of the throat, convergence, and divergence angle) with three-dimensional simulations were studied in 2022 by Abbas-Shiroodi et al. 15 In 2022, numerical investigation of a rotating reactor with a movable tooth and a fixed tooth was done by Fu et al. 16 In 2022, a swirling vortex cavitator was designed by Wang et al. 17 and its three-dimensional CFD simulation was carried out. ...
... It is worth mentioning that P in these equations denotes local far-field static pressure. For the condensation process, the net mass transfer rate is also defined by Eq. (15). The final form of evaporation and condensation mass transfer rates, R e and R c , are defined in the following equations: if P v ! ...
Hydrodynamic cavitation is an efficient method in terms of energy consumption that can be used to intensify the pollutant degradation processes in wastewater treatment. Among various kinds of cavitation reactors, a swirling jet-induced cavitation reactor that has been less studied was investigated in detail for the first time in this work. Recently, researchers have focused more on investigating the parameters that affect the process and control its intensity. In the present work, the efficacy of the operating pressure on the performance of the cavitating device was investigated by calculating the cavitational efficacy ratio (CER) using full three-dimensional computational fluid dynamics simulations. Also, preliminary studies were carried out for the first time to optimize the curvature correction coefficient of the shear stress transport k–ω viscous model to sensitize it to streamline curvature to obtain convergence and stability of the simulations. The optimum operating pressure was found by solving the cavity dynamics equations and calculating the CER parameter. The Rayleigh–Plesset cavity dynamics equation was applied to the cavity trajectory obtained from solving the discrete phase model to track the cavity radius and inside pressure variations. Finally, the validation of the simulation and estimated optimum operating pressure were done by the experimental data reported in the literature that there was reasonable agreement between them.
... Currently, cavitation plays an important role in addressing the issue of wastewater [5,6]. The localized high temperature and high-pressure environment created by cavitation bubble collapse can cause the water molecules near the bubble surface to pyrolyze into hydroxyl and hydrogen free radicals, which then have the effect of oxidizing organic pollutants in the water body through the diffusion of hydroxyl free radicals in the liquid medium [7]. Various studies have assessed the efficacy of cavitation in wastewater treatment: Innocenzi et al. [8] carried out laboratory-scale research on the effectiveness and possibility of treating methyl orange solution with cavitation of the Venturi tube; their results demonstrated that the cavitation induction into the oxidation process can improve dye degradation under regulated operating settings. ...
... In the presence of cavitation, the flow in a Venturi tube is a combination of vapor and liquid phases. To describe the two-phase flow of vapor and liquid in a Venturi tube, the mixture model is applied [7,15,21,26]. Based on this, a hypothesis is proposed, which assumes that the vapor and liquid phases are homogeneously mixed and able to permeate each other, regardless of their relative velocities. ...
Cavitation is a typical physical process that has shown to be highly valuable in the wastewater treatment field. This study aims to investigate the effects of the converging and diverging sections of a Venturi tube on the cavitation flow field. Multiphase flows in tubes are presented using the mixture model and the standard k-ε model. And the Schnerr and Sauer cavitation model is employed to simulate the vapor–liquid phase transition process. Both grid independence and the numerical method’s feasibility were validated before the research. The results showed that the influence of the divergence section length on Venturi cavitation characteristics depends on the provided pressure conditions. As the pressure increases, shorter divergence sections result in more significant cavitation effects. The length of the convergence section displays various cavitation behaviors under different pressure situations. A small contraction section length can achieve better cavitation effects in high-pressure applications, whereas the opposite is true in low-pressure cases. Within the scope of this study, it was observed that the Venturi tube with a divergent section of 14 Lt and a convergent one of 2.4 Lt provided enhanced cavitation performance when subjected to inlet pressures ranging from 0.8 to 1.2 MPa. Our findings indicate that the selection of converging and diverging section lengths in Venturi tubes should consider the corresponding operational pressure conditions, which provides valuable guidance and engineering significance in the research and development of Venturi cavitation devices in hydraulic engineering.
... In previous papers, the authors demonstrated hydrody-namic cavitation's efficiency in degrading methyl orange dye (MO) [35][36][37][38] . MO or Sodium 4-[(4-dimethylamino) phenyldiazenyl] benzenesulfonate is an azo dye soluble in water; it is used in textile production and is a residue in industrial wastewater. ...
Hydrodynamic cavitation is a promising technology for several applications, like disinfection, sludge treatment, biodiesel production, degradation of organic emerging pollutants as pharmaceutical, and dye degradation. Due to local saturation conditions, cavitating liquid exhibits generation, growth, and subsequent collapse of vapor-filled cavities. The cavities' collapse brings very high pressure and temperature; this last aspect is essential in some chemical processes because it induces the decomposition of water molecules into species with a high oxidation potential, which can react with organic substances. Properly exploiting this process requires a highly accurate prediction of pressure peak values. To this purpose, we implemented a multi-phase Eulerian–Lagrangian code to solve the fluid-dynamic problem, coupled with the Rayleigh–Plesset equation, to capture the evolution of bubbles with the required accuracy. The algorithm was validated against experimental data acquired with optical techniques for different cavitation-shedding mechanisms. Then, we used the developed tool to investigate the decoloration of organic substances from a cavitation Venturi tube operating at different pressure. We compared the obtained results with the experimental observation to assess the reliability of the developed code as a predictive tool for cavitation and the possibility of using the code itself to assess scale-up criteria for possible industrial applications.
... To accurately capture the formation of vapor in the hydrodynamic cavitation process, a mixture model was used. This model allows the gas phase to interpenetrate into the liquid phase, where relative velocities are not taken into consideration as in cavitation flows [32][33][34][35]. In the mixture model, a single momentum equation is used to solve for a homogeneous mixture of liquid and vapor phases. ...
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.
... These two parameters are defined according to the following Eqs. [99]. The total perimeter of holes shows the area occupied by the shear layer and it has been proved that the turbulence in shear layer and the section occupied by it are the key factor influencing cavitation yield [83]. ...
... Although it has been reported that an increase in increases the effectiveness of cavitation, it is not appropriate for all applications [100]. Hence, several studies in the literature have recommended optimizing this value in different applications [99,[101][102][103]. values of 2 [83,104,105], 4 [98,106,107], and 1.333 [97] have been reported in the literature. ...
... The maximum size of bubbles and their lifetime are dependent on the design of divergent section. The divergence angle impacts the pressure profile and pressure recovery and can be adjusted to control the collapse of bubbles [99]. An increase in the divergence angle accelerates the pressure recovery, which means a larger divergence angle results in the rapid collapse of bubbles. ...
Conversion of food wastes to valuable products is an important topic for sustainable development. Feedstock hydrolysis is a stage strongly affecting the anaerobic digestion process, and resistance of food waste towards hydrolysis causes a decrease in product yield. such as biomethane, biohydrogen, biohythane, VFAs, and lactic acids. Moreover, mass transfer is a serious limitation of transesterification for the production of biodiesel. Cavitation is a promising pretreatment method for the mitigation of these issues. This work presents a critical review on cavitation-assisted processing of food waste. In several studies, cavitation proved its remarkable potential.
Cavitation can also be employed in anaerobic digestion reactors and directly irradiate microorganisms, stimulating enzyme activities. Cavitation led to an increase in SCOD by up to 172%. Consequently, it caused an increase in biogas, biohydrogen, VFAs, and lactic acid converted from food waste by up to 100%, 145, 100%, and 62%, respectively. Cavitation resulted in a reduction in reaction time required for the conversion of food waste into biodiesel by up to 98% due to its potential in increasing mass transfer. In acoustic cavitation, the optimum power density for the conversion of food waste through anaerobic digestion is in ranges of 230-480 W/L and 40-50 W/L at pretreatment stage and main stage, respectively. Low frequencies in a range of 20-50 kHz are suitable for both anaerobic digestion and transesterification. However, studies on the application of high frequency are scarce and obvious “research-gap” in this field exists. In hydrodynamic cavitation, for disintegration, efficient cavitation number and pressure are in ranges of 0.07-0.15 and 2-4 bar, respectively. The maximum particle size reduction usually occurs within the initial 15 min for both types of cavitation.
... This phenomenon can cause filled cavitation zone with a high number of cavities that usually contain the molecules of water vapor in the form of cavitation cloud. Despite an increase in cavities produced by an increase in pressure drop, cavity cloud is not able to collapse and create the extreme conditions that are responsible for decolorization [60,61]. The trend can also be explained by Cavitation number (C v ). ...
Decolorization of Ponceau 4R, Tartrazine, and Coomassie Brilliant Blue (CBB) was studied using hybrid processes of hydrodynamic cavitation (HC) with potassium persulfate (KPS) and hydrogen peroxide (H2O2). The different properties of these dyes such as hydrophobicity, molecular structures, and molecular weights provided this opportunity to investigate the effects of these factors by comparing the decolorization values of the dyes. Treatment process was optimized in respect to cavitation number, HC inlet pressure, and the concentration of external oxidants. The application of dual oxidation system under cavitation conditions revealed a synergetic effect. Maximum decolorization values of 92.27%, 50.1%, and 42.3% were obtained applying this combined process for CBB, Tartrazine, and Ponceau 4R, respectively. The different values of decolorization of the dyes were explained based on their different properties. The kinetic study led to first order rate constants of 10⁻³ min⁻¹, 6.4*10⁻³ min⁻¹, 9.2*10⁻³ min⁻¹, and 4.16*10⁻² min⁻¹ using KPS, H2O2, HC, and HC-KPS-H2O2, respectively. A synergetic coefficient of 2.51 obtained by HC-KPS-H2O2 proved the effectiveness of this combined process. Analysis of cavitation yield efficiency showed an improvement of 98% for the HC-KPS-H2O2 combined process as compared to sole HC treatment process.
... There are numerous two-dimensional (2D) CFD studies in the literature for the venturi devices in hydrodynamic cavitation [19][20][21]. In addition, many CFD studies have examined the hydrodynamic cavitation in the 2D axis symmetric framework for the single hole orifice plate [22,23]. ...
... In the Euler-Euler mixture model, a volume fraction is introduced since one phase cannot occupy another. Accordingly, a transport equation of (5) is solved to calculate the volume fraction [21,22]. Bubble growth/collapse is solved using a simplified Rayleigh-Plesset equation [35]. ...
The hydrodynamic cavitation (HC) as an influential advanced oxidation technology is commonly used for treating organic wastewater. In the present research, a CFD model is used to study the hydrodynamic cavitation in multi-hole orifice (MHO). Accordingly, the effect of hole-to-hole interaction in MHO and its influence on the bubble generation and the flow turbulence downstream of the orifice are analyzed. During the cavitation, the central hole exhibits the highest flow rate, i.e., strong jet, over other jets for the dimensionless hole's pitch circle, δ, equal to 50 and 75%. This causes the occurrence of the pitchfork bifurcation phenomenon, and thereby a high level of turbulence intensity behind MHO especially for δ=50%. The value of δ also affects the streamlines curvature at the hole entrance. This curvature influences on the bubble generation due to a reduction in the pressure gradient. The bubble distribution is not uniform at the entrance of each holes because of non-uniform flow separation at the tip holes. The minimum cavitation number and pressure loss are obtained at δ equal to 50%. The MHO thickness, tD =0.5, provides more guidance to the outlet jet and thereby a decrease of the jet's interaction. Also, the results show the significant impact of MHO thickness on the issued jet, which in turn affects the turbulence intensity (i.e., bubble life). Alternatively, increasing the number of holes rather than using larger holes leads to more bubble formation from each hole when the opening area ratio remains constant. Finally, the change in operating conditions of the inlet pressure and the working temperature is studied and the results are discussed.
... Looking at some recent examples of utilizing CFD [12][13][14][15][16][17][18][19][20] to interpret the results and facilitate the optimization process reveals that on one side researchers approach the modeling of very complex geometries (rotor-stator interaction, narrow gaps, high-frequency oscillations, swirls), but on the other employ a very rudimentary modeling approach (steady flow approach, very basic turbulence modeling, and even assuming laminar flow conditions and no cavitation modeling). Furthermore, rarely studies of mesh independence and convergence criteria are included in the manuscript, and all too often the boundary conditions are not detailed enough. ...
The research on the potential of cavitation exploitation is currently an extremely interesting topic. To reduce the costs and time of the cavitation reactor optimization, nowadays, experimental optimization is supplemented and even replaced using computational fluid dynamics (CFD). This is a very inviting opportunity for many developers, yet we find that all too often researchers with non-engineering background treat this “new” tool too simplistic, what leads to many misinterpretations and consequent poor engineering.
The present paper serves as an example of how complex the flow features, even in the very simplest geometry, can be, and how much effort needs to be put into details of numerical simulation to set a good starting point for further optimization of cavitation reactors. Finally, it provides guidelines for the researchers, who are not experts in computational fluid dynamics, to obtain reliable and repeatable results of cavitation simulations.
