Cavitation Phenomenon Research Articles

Laser-Produced Cavitation Bubble Behavior in Newtonian and Non-Newtonian Liquid Inside a Rigid Cylinder: Numerical Study of Liquid Disc Microjet Impact Using OpenFOAM.

This study employs OpenFOAM to analyze the behavior of a single laser-produced cavitation bubble in a Newtonian/non-Newtonian fluid inside a rigid cylinder. This research aimed to numerically calculate the impact of liquid disc microjet resulting from the growth and collapse of the laser-produced bubble to the cylinder wall to take advantage of the cavitation phenomenon in various industrial and medical applications, such as modeling how to remove calcification lesions in coronary arteries. In addition, by introducing the main study cases in which a single bubble with different initial conditions is produced by a laser in the center/off-center of a cylinder with different orientations relative to the horizon, filled with a stationary or moving Newtonian/Non-Newtonian liquid, the general behavior of the bubble in the stages of growth and collapse and the formation of liquid disk microjet and its impact is examined. The study demonstrates that the presence of initial velocity in water affects the amount of microjet impact proportional to the direction of gravity. Moreover, the relationship between the laser energy and the initial conditions of the bubble and the disk microjet impact on the cylinder wall is expressed.

A refined numerical investigation of a large equivalent shallow-depth underwater explosion

The large equivalent shallow-depth explosion problem is very significant in the field of naval architecture and ocean engineering, as such explosions can be used to attack and demolish ships and anti-ship missiles. In the current work, a refined numerical study of the flow-field characteristics of a large equivalent shallow-depth explosion is carried out using a self-developed Eulerian finite element solver. First, the numerical model is validated against theoretical results and a small equivalent explosion test in a tank. The numerical results are found to agree well with the theoretical and experimental results. In the next step, the cavitation cut-off effect is added to the underwater explosion model, and the cavitation phenomenon is quantitatively analyzed through the flow-field pressure. In addition, the dynamic characteristics of the bubble and water hump under various initial conditions for different stand-off parameters are analyzed. The effect of gravity on these physical processes is also discussed. The bubble pulsation period, taking into account the free surface effect, is then quantitatively studied and compared with Cole’s experimental formula for an underwater explosion. Overall, when the stand-off parameter γ > 2, the influence of the free surface on the empirical period of the bubble is not significant. Our investigation provides broad insights into shallow-depth underwater explosions from theoretical, experimental, and numerical perspectives.

Concentration and cavitation in the vanishing pressure limit of solutions to the relativistic Euler equations with the logarithmic equation of state

In this paper, we constructively solve the Riemann problem for the relativistic Euler equations with the logarithmic equation of state. The concentration and cavitation phenomena are observed and analyzed during the process of vanishing pressure in the Riemann solutions. It is rigorously proved that, as the pressure vanishes, they tend to the two kinds of Riemann solutions to the zero-pressure relativistic Euler equations, which include a delta shock formed by a weighted δ-measure and a vacuum state.

Numerical simulations of cavitating water jet by an improved cavitation model of compressible mixture flow with an emphasis on phase change effects

Focusing on cavitation phenomena caused by high-speed submerged water jets, this paper presents an improved cavitation model for a compressible fluid mixture based on a concise estimation of fluid compressibility that considers phase change effects. The homogeneous two-phase flow assumption is adopted, and the gas phase is assumed to consist of vapor and non-condensable components. Equations of state for a pure liquid and an ideal gas are employed to evaluate the compressibility of the liquid and non-condensable components, and the compressibility of the vapor is treated semi-empirically as a constant. The model is embedded in an unsteady Reynolds-averaged Navier–Stokes solver, with the realizable k-ε model employed to evaluate the eddy viscosity. The turbulent cavitating flow caused by an impulsively started submerged water jet is treated. The pattern of periodic cavitation cloud shedding is acceptably captured, and the mass flow rate coefficient and its fluctuation frequency evaluated by simulations agree with the experimental results well. The validity of the proposed method is confirmed. The results reveal that cavitation occurs when pin/Pin reaches 0.65 and fluid flow begins to pulsate. In the well-developed stage, the leading cavitation cloud and a subsequent cloud are successively shed downstream, and this process is repeated. The subsequent cloud catches the leading cloud, and they coalesce in the range x/d≈ 2–3. The pressure fluctuations concentrate in the range of x/d≈2–5 corresponding to the periodic shedding of cavitation clouds. The mass flow rate coefficient pulsates from 0.59–0.66 under the effect of cavitation.

Effect of cloud transits in a stand-alone solar photovoltaic water pumping system

This paper discusses the effects of cloud transit on a stand-alone direct solar photovoltaic water pumping system for irrigation and farms. In this way, its impact is studied, applying a possible classification based on its incidence and effects on the system. For this, the information provided by the data loggers of different photovoltaic installations has been analyzed and in turn compared with the data obtained in the reference installation. In addition, the Matlab-Simulink simulation model used is described. Different simulations have been developed to verify the basic characteristics of the proposed system. In this way, it is possible to check the advantages and drawbacks of the direct water pumping in irrigation applications. At the same time, the system parameters can be easily modified to meet the requirements of different water flow capacities. Also, the water hammer effect and the cavitation phenomenon in the water pump are described. Finally, the simulation results obtained as well as their conclusions are presented.

Ultrasonic Decontamination of Chemical Warfare Agents

Abstract Sonochemistry studies the physical and molecular level changes induced by ultrasonic energy on solutions. Sonochemical degradation of the chemical warfare agents (CWA) may occur due to three successive phenomena based on the principles of acoustic cavitation phenomena: nucleation, growth, and implosive collapse of microbubbles. The sonolytic degradation of CWA was quantified by GC-MS technique, considering the variation of some parameters such as frequency of ultrasonic waves, power control, temperature, and addition of nanoparticles as catalysts to the solution.

Generation and Evolution of Cavitation Bubbles in Volume Alternate Cavitation (VAC)

Cavitation generation methods have been used in multifarious directions because of their diversity, and numerous studies and discussions have been conducted on cavitation generation methods. This study aims to explore the generating mechanism and evolution law of volume alternate cavitation (VAC). In the VAC, liquid water is placed in an airtight container with a variable volume. As the volume alternately changes, the liquid water inside the container continues to cavitate. Then, the mixture turbulence model and in-cylinder dynamic grid model are adopted to conduct computational fluid dynamics simulation of volume alternate cavitation. In the simulation, the cloud images at seven heights on the central axis are monitored, and the phenomenon and mechanism of height and eccentricity are analyzed in detail. By employing the cavitation flow visualization method, the generating mechanism and evolution law of cavitation are revealed. The synergistic effects of experiments and high-speed camera capturing confirm the correctness of the simulation results. In the experiment, the volume change stroke of the airtight container is set to 20 mm, the volume change frequency is 18 Hz, and the shooting frequency of the high-speed camera is set to 10000 FPS. The experimental results indicate that the position of the cavitation phenomenon has a reasonable law during the whole evolution cycle of the cavitation cloud. Also, the volume alternation cycle corresponds to the generation, development, and collapse stages of cavitation bubbles.

Effect of the pipe bend of the morning glory spillway on the cavitation number

Cavitation phenomena always threats the hydraulic structures with high velocity flow and suddenly varying the flow direction. It is assumed that the process of the flow depleting with high ratio through the morning glory spillway accompanied by suddenly varying the flow direction caused by the bend pipe can deteriorate the condition of the cavitation. Introducing the ratio R/D (diameter size of the vertical and horizontal shaft divided with radius of the bend pipe) can be beneficial to propose the novel design plan to avoid the cavitation caused by the bend pipe. Present study carried out a series experimental tests to validate a numerical model of the morning glory spillway with different R/D ratio to show the impacts of the suddenly varying the flow direction on the variation of the cavitation number. The cavitation values of the free, semi-submerged and submerged flow conditions showed that cavitation was mainly occurred on the internal arch of the bend pipe for free flow and the level of the danger for semi-submerged flow was the major danger level for internal arch of the bend pipe and due to submerged flow, the crest level at the entrance of the morning glory spillway was additionally threated by cavitation. To prevent from the cavitation, the values of the cavitation number due to different R/D as 0.55, 0.45, 0.35, and 0.25 were calculated by employing the validated numerical model due to high danger of the cavitation in semi-submerged condition. Results showed that due to D/R > 0.35, the possible cavitation damage is obtained for the internal and external arch of the bend pipe of the morning glory spillway; however, for D/R < 0.25, the bend pipe position is located in safe zone and the danger of the cavitation is negligible.

Experimental and Numerical Study on Cavitation Effects in Centrifugal Pumps

Experimental and numerical investigations of the centrifugal pump performance at non-cavitating and cavitating flow conditions were carried out in the present study. Experiments were performed by applying a vacuum to a closed-loop system to investigate the effects of the net positive suction head available (NPSHa), flow rate, water temperature and pump speed on the centrifugal pump performance. Accordingly, many of the important parameters concerning cavitation phenomenon were calculated. Also, the noise which is accompanied by cavitation was measured. Numerical analysis was implemented for two phase flow (the water and its vapor) using a 2-D simulation by ANSYS FLUENT software to investigate the internal flow of centrifugal pump under cavitating conditions. It was observed that with decreasing NPSHa, the values of the pump head, flow rate and efficiency initially remain constant, but with further reduction in NPSHa these parameters will decrease. Also, it was found that at 3% head drop the percentage drop of the flow rate is less than 2% whereas the percentage drop of the efficiency is greater than 3%. Numerically, it was noticed that the cavitation regions appear at the leading edge of suction side of the impeller blades which represents the lowest pressure area inside the computational domain of the centrifugal pump.

Study on boundary reflection mechanism of continuous wave mud pulse in the flow loop

Continuous wave (CW) mud pulse is one of the essential ways of high speed data transmission while drilling. The boundary reflection process and mechanism need to be clarified, which seriously affects the analog interpretation of pressure waves in flow loops and drilling conditions. In this paper, the boundary reflection of mass inlet and pressure outlet is studied by using traditional acoustic theory and numerical simulation methods, and mutual verification is carried out with flow loop. The results show that the pressure wave generated by the CW generator can be divided into compression wave and expansion wave and transmitted to the upstream and downstream pipelines. The inlet boundary reflection is the hard boundary reflection in acoustics. The phase of reflected wave is the same as that of the incident wave. The outlet boundary is the soft boundary, the reflected wave phase is 180° opposite to the incident wave. In particular, the process and mechanism of secondary reflection of stator and rotor structure on pressure wave are analyzed for the first time, which provides a theoretical basis for pressure wave amplitude. Finally, due to the possibility of cavitation phenomenon in the flow loop, it is different from the pressure environment of the bottom under drilling conditions and should to study further.

Hydrodynamics and Transport Mechanism of Microfluidic Mixing in Precipitation of Nanodrugs: A Review

AbstractPoor aqueous solubility drugs are a concern of pharmaceutical industries due to low dissolution rates and low bioavailability. Various approaches and techniques address these issues by customizing drug micro–nanonization, as investigated by many researchers. Establishing a compelling synthesis of tailored nanoparticles with highly variable qualities intended for therapeutic applications needs the flexibility to vary particle size, content, crystallinity, and shape. Such an approach necessitates getting to the desired yield and developing a synthetic process that is durable, reproducible, and scalable. However, precipitation techniques to produce nanoparticles are more convenient than other approaches. Liquid antisolvent precipitation is one of the robust crystal manipulation approaches extensively used for producing nanoparticles, where mixing sets the basis to create supersaturation followed by corresponding quality precipitation. Various process intensification equipments are in use for adequate mixing‐based precipitation. Nowadays, microfluidic precipitation system is gaining interest in the production of nanodrugs. Further, the use of ultrasound in a microfluidic system improves the mixing quality by cavitation phenomena. This review focuses on the transport phenomena and hydrodynamics involved in mixing to enhance the mass transfer during antisolvent precipitation of synthesized nanodrugs in the microfluidic system.

A Numerical Investigation of Supercavitation Vehicle’s Hydrodynamic Noise

This paper presents the simulation results of the acoustic field around an underwater supercavitation vehicle under various operating conditions and analyzes the cavitation phenomenon and the hydrodynamic noise spectrum. Regarding the ventilated cavitation phenomenon, the simulation shows that low vehicle speed can reduce the threshold of the ventilated supercavitation, and high background pressure can enhance the stability of the supercavitation structure. As for hydrodynamic noise, firstly, the simulation results reveal that when cavitation occurs, the noise spectrum exhibits several characteristic peaks near 1 kHz and between 3 and 10 kHz. The overall noise amplitude demonstrates a descending trend between 10 and 40 kHz. Further, under natural cavitation conditions, a characteristic peak is detectable between 40 and 80 kHz. The influence of the operating conditions on the noise is essentially achieved by altering the scale of the cavitation flow: with the growth of the bubble flow scale, the noise between 3 and 10 kHz first increases and then decreases due to its own pulsation and the masking effect, while the noise between 10 to 40 kHz substantially reduces. On the other hand, if the scale expansion of bubble flow is related to the increase of ventilation flow, the noise amplitude near 1 kHz will increase significantly. These results provide theoretical support for studying the supercavitation vehicles’ noise and applying the ventilated supercavitation technology.

Revealing the influence of ultrasonic processing on the kinetic parameters of convective and combined drying of raw apple materials

The object of research is the process of convective and combined drying of apple raw materials treated before dehydration in an ultrasonic bath. The use of pretreatment solves the issue of intensifying the dehydration process and maintaining the quality of the product. Sonication for 5 min reduces the dehydration process by 13.7 %, and at 10 min processing – by 27.8 % compared to traditional convective drying. With increasing processing time to 20 minutes, the dehydration rate deteriorates. Sonication of raw materials for 5 minutes under combined heating does not intensify the dehydration process, and within 10 and 20 minutes it reduces the efficiency of moisture removal. When processed for 10 minutes, the time to reach the final moisture content is increased by 17.2 %, and at 20 min – by 23.4 % compared to control samples. Regardless of the processing time, there is a decrease in the maximum temperature of the samples in the combined drying process. When processed for 5 minutes, the maximum temperature of the samples decreased by 4.3 %, and with 10 and 20-minute processing – by 8.6 % and 12 % compared to the temperature of samples without sonication. The results are explained by the "sponge effect" caused by ultrasonic vibrations and the phenomenon of cavitation that occurs in the liquid during the action of the ultrasonic field. The peculiarity of the pre-sonication before drying is the possibility to intensify the convective dehydration process without increasing the heat carrier's temperature. The use of this type of processing in a combined energy supply will solve the problem of preserving the quality of the finished product by reducing the maximum temperature of the raw material. The research reported here could be a prerequisite for practial design of an energy-efficient electrical system for drying fruit and vegetable raw materials.

Investigation on cutting performance in ultrasonic assisted helical milling of Ti6Al4V alloy by various parameters and cooling strategies

Ti6Al4V alloy is one of the typical difficult-to-machine materials and often results in rapid tool wear, leading to poor machining quality in aircraft assembling. Compared to conventional helical milling, the ultrasonic assistant helical milling (UAHM) process has indicated its superior performance; however, it is still a great challenge to improve the hole surface quality and accuracy. In addition, few studies have been conducted on the effect of different variables and cooling strategies on the hole-making performance in longitudinal-torsional ultrasonic assisted helical milling (LT-UAHM). This paper, for the first time, reports effects of machining variables on geometric precision and surface roughness in LT-UAHM of Ti6Al4V. In addition, the lubrication/cooling mechanism on the simultaneous application of LT-UAHM and MQL is theoretically analyzed. The design approach of Taguchi experiment was employed to study how major variables such as the cutting speed, tangential feed, axial feed, and the workpiece hardness influence the dimensional and geometrical tolerances and surface roughness. This paper also discussed the effect of three cooling strategies, i.e., dry condition, air coolant, and minimum quantity lubrication (MQL) in LT-UAHM. Theoretical analysis demonstrated that the MQL coolant can be nebulized into hyper-fine droplets owing to the resonant cavitation phenomenon. Combined with the penetrating action caused by the separate-cutting principles of LT-UAHM, the cooling and lubrication performance of MQL was further enhanced. As a result, LT-UAHM with MQL had the most positive effect on circularity, cylindricity, nominal diameter, and surface roughness, contributing to 34%, 32%, 39%, and 40%, respectively. The second important machining factor was the cutting speed, contributing to 31%, 29%, 36%, and 22%, respectively. The tangential feed and workpiece hardness have the negative effect on geometrical accuracy, respectively.

Development of fast scanning module with a novel bubble solution applied to scanning acoustic microscopy system for industrial nondestructive inspection

Scanning acoustic microscopy (SAM) system is a powerful nondestructive instrument owing to its capability to provide internal information and defect positions inside a material. In industrial applications of SAM, the scanning time plays an important role in enhancing efficient inspection of the product line. Several studies have used the traditional SAM system, which develops based on linear motor to inspect industrial samples, but the inspection time remained relatively long and cost-prohibitive. Herein, we reported a low-cost fast SAM (FSAM) system that provided the image results in a short time while maintaining their high resolution. In this design, FSAM fast scanning module (FSM) was developed by exploiting the slider-crank mechanism, which was optimized for a specific product to substantially reduce the inspection time. During the scanning process, bubbles were generated due to the rapid movement of transducer into the water, namely the bubble cavitation. The bubbles restricted the ultrasound wave propagation, which resulted in the bad image quality. The bubble cavitation phenomenon was examined using the incompressible flow theory to investigate the bubble inception, which was defined based on the pressure value around transducer. The bubbles appeared in areas where the pressure less than the vapor pressure. Using the OpenFOAM to analyze the pressure value, the bubble problem was solved by a novel solution that used a bubble reduction plate attaching to the transducer. The coin and aluminum samples with known dimensions and internal structure were prepared to scan using the FSAM system, which validated the simulation results and FSAM capabilities in providing good images with internal information and accurate measurements. Finally, FSAM system was designed and developed to successfully inspect industrial samples in a short time, such as an integrated circuit chip, printed circuit board, welded sheets, and silicon wafer. Using the FSAM system to scan welded sheets, the scanning time were reduced by approximately 77% compared to the traditional SAM system. These results demonstrate that the FSAM system is a potential instrument for industrial nondestructive inspection.

Failure mechanism of single pile-friction footing hybrid foundation under combined V–H–M loadings by PIV experiments and FE method

The traditional monopile foundation is confronted with challenges in the context of the new generation of offshore wind turbines with greater power capacities. On this basis, the single pile-friction footing hybrid foundation is investigated, whose bearing capacity is largely improved by combining a circular friction footing at the mudline. This paper discusses the failure mechanisms and bearing capacities of this hybrid foundation in sand under combined vertical-horizontal-moment (V–H-M) loadings by laboratory experiments and the finite element method. By adopting Particle Image Velocimetry (PIV) technology in model tests, failure mechanisms of a single pile and the hybrid system are compared. The results show that the cavitation and compaction phenomenon can be captured in the depth range of 0–0.7 pile embedment depth) for the hybrid foundation. Also, due to the settlement of the footing, a deformation area with a concave area and a small peak value can be found under the footing, which is quite different from that of the pile under V–H-M combined loadings. Intensive parametric studies were performed through FE method, and the results indicate that increasing the footing diameter has a more pronounced effect on the bearing capacity compared to that of increasing the length-diameter ratio of the pile.

Study of wear processes generated by cavitation phenomena produced by laser induced dielectric breakdown on borided and non-borided 316L stainless steel surfaces in bi-distilled water

This work presents a study of the wear of borided and non-borided 316L stainless steel surfaces produced by the cavitation and thermal effects caused by the laser induced dielectric breakdown using bi-distilled water as the dielectric medium. A pulsed beam of a high-power laser was focused at a different distance between the surfaces and the focus spot in a parallel configuration. The wear produced on the non-borided surface presented the combination of both cavitation and thermal effects that decreased with the increase of the surface-focus spot distance. On the other hand, the borided surfaces showed a higher thermal resistance due to that worn areas presented just the erosion of the material by the cavitation process, as revealed by the microstructure of the boride surfaces.

Investigation on acoustic, thermal, and tribological properties of hydrodynamic journal bearing with heterogeneous rough/smooth surface

High level of noise limits the reliability of the lubricated journal bearing. In the current paper, the possibility of bearing design with a heterogeneous rough/smooth surface is explored using the computational fluid dynamics (CFD) approach to improve tribological and acoustic performance. A parametric analysis is conducted to determine the optimal surface roughness level, the cavitation pressure, and the ratio of length to the diameter of the journal. The effect of the presence of a roughened pattern on the thermal behavior of the lubricant, friction force, noise level, and cavitation phenomena was also studied in depth. The main finding of the present study is that when conventional journal bearing fails in generating the load support for concentric conditions, the heterogeneous rough/smooth bearing has a beneficial effect by increasing the load-carrying capacity. Furthermore, the high level of surface roughness can significantly increase the load-carrying capacity while decreasing frictional forces and acoustic power. However, the roughness does not dramatically change the maximum temperature (less than 1%). The numerical results also suggest that the variation in vapor saturation pressure has a negligible effect on the maximum temperature, friction force, and noise level.

Advancing Process Intensification with High-Frequency Ultrasound: A Mini-Review of Applications in Biofuel Production and Beyond

High-frequency ultrasound (HFU) is an ultrasound technology with a frequency higher than 1000 kHz. It has become increasingly recognized as an emerging process intensification technology in various fields, such as biofuel production, carbon dioxide absorption, and wastewater treatment. HFU is seen as a potential intensifier technology for biofuel production, as its mechanisms, such as cavitational phenomena, microstreaming, and fountain formation, can benefit biofuel production. Previous research has shown that HFU can decrease the reaction time required for biofuel production, aid in lipid extraction, increase carbon dioxide absorption rates, and be effective in destroying pathogens in wastewater treatment. However, despite the potential benefits, there are limited reports on the use of HFU technology for biofuel production, which has led to uncertainties and constraints in its industrial deployment. These constraints include equipment design, economic analysis, and safety concerns, which require further in-depth analysis. Despite these limitations, previous studies have shown promising results for the incorporation of HFU into various fields due to its unique characteristics and mechanisms. This paper presents a review of the theory and application of HFU for process intensification, with a focus on its potential for biofuel production. It also provides recommendations for the further exploration of the technology to overcome industrial deployment obstacles.

Water treatment by cavitation: Understanding it at a single bubble - bacterial cell level

Cavitation is a potentially useful phenomenon accompanied by extreme conditions, which is one of the reasons for its increased use in a variety of applications, such as surface cleaning, enhanced chemistry, and water treatment. Yet, we are still not able to answer many fundamental questions related to efficacy and effectiveness of cavitation treatment, such as: “Can single bubbles destroy contaminants?” and “What precisely is the mechanism behind bubble's cleaning power?”. For these reasons, the present paper addresses cavitation as a tool for eradication and removal of wall-bound bacteria at a fundamental level of a single microbubble and a bacterial cell. We present a method to study bubble-bacteria interaction on a nano- to microscale resolution in both space and time. The method allows for accurate and fast positioning of a single microbubble above the individual wall-bound bacterial cell with optical tweezers and triggering of a violent microscale cavitation event, which either results in mechanical removal or destruction of the bacterial cell. Results on E. coli bacteria show that only cells in the immediate vicinity of the microbubble are affected, and that a very high likelihood of cell detachment and cell death exists for cells located directly under the center of a bubble. Further details behind near-wall microbubble dynamics are revealed by numerical simulations, which demonstrate that a water jet resulting from a near-wall bubble implosion is the primary mechanism of wall-bound cell damage. The results suggest that peak hydrodynamic forces as high as 0.8 μN and 1.2 μN are required to achieve consistent E. coli bacterial cell detachment or death with high frequency mechanical perturbations on a nano- to microsecond time scale. Understanding of the cavitation phenomenon at a fundamental level of a single bubble will enable further optimization of novel water treatment and surface cleaning technologies to provide more efficient and chemical-free processes.