Level Of Cavitation Research Articles

Off-Design Operation and Cavitation Detection in Centrifugal Pumps Using Vibration and Motor Stator Current Analyses.

Centrifugal pumps are essential in many industrial processes. An accurate operation diagnosis of centrifugal pumps is crucial to ensure their reliable operation and extend their useful life. In real industry applications, many centrifugal pumps lack flowmeters and accurate pressure sensors, and therefore, it is not possible to determine whether the pump is operating near its best efficiency point (BEP). This paper investigates the detection of off-design operation and cavitation for centrifugal pumps with accelerometers and current sensors. To this end, a centrifugal pump was tested under off-design conditions and various levels of cavitation. A three-axis accelerometer and three Hall-effect current sensors were used to collect vibration and stator current signals simultaneously under each state. Both kinds of signals were evaluated for their effectiveness in operation diagnosis. Signal processing methods, including wavelet threshold function, variational mode decomposition (VMD), Park vector modulus transformation, and a marginal spectrum were introduced for feature extraction. Seven families of machine learning-based classification algorithms were evaluated for their performance when used for off-design and cavitation identification. The obtained results, using both types of signals, prove the effectiveness of both approaches and the advantages of combining them in achieving the most reliable operation diagnosis results for centrifugal pumps.

The role of cavitation in the toughening of elastomer nanocomposites reinforced with graphene nanoplatelets

The toughening of different types of elastomers through the incorporation of graphene nanoplatelets (GNPs) has been investigated. Both the tear strength and tearing energy are increased significantly through a combination of mechanisms such as debonding, pull-out and cavitation. The processes that occur ahead of a tear/crack tip in natural rubber filled with GNPs have been monitored in situ using synchrotron-based nanoscale X-ray computed tomography. The GNP particles are found to debond and form voids that grow under stress leading to considerable energy absorption. The mechanisms of cavitation and void growth are analysed theoretically and it is shown that voids need to be larger than ∼1 μm in size to grow in the triaxial tensile stress field ahead of the tear/crack tip. The high level of cavitation and void growth found for the elastomers filled with micron-sized GNP particles is suggested to be the reason why these nanocomposites have a high tear resistance.

Experimental Investigation of the Effect of Suction Valve Opening on the Performance and Detection of Cavitation in the Centrifugal Pump Based on Acoustic Analysis Technique

The pump performance and occurrence of cavitation directly depends on different operating conditions. To cover a wide range of operation conditions for detecting cavitation in this work, investigations on the effect of various suction valve openings on cavitation in the pump were carried out. In order to analyse various levels of cavitation in different operation conditions, the effect of the decrease in the inlet suction pressure of the centrifugal pump by controlling the inlet suction valve opening was investigated using this experimental setup. Hence, the acoustic and pressure signals under different inlet valve openings and different flow rates, namely, 103, 200, 302 l/min were collected for this purpose. A detailed analysis of the results obtained from the acoustic signal was carried out to predict cavitation in the pump under different operating conditions. Also, the acoustic signal was investigated in time domain through the use of the same statistical features. The FFT technique was used to analyse the acoustic signal in the frequency domain. In addition, in this work an attempt was made to find a relationship between the cavitation and noise characteristics using the acoustic technique for identifying cavitation within a pump.

Experimental Comparative Investigations to Evaluate Cavitation Conditions within a Centrifugal Pump Based on Vibration and Acoustic Analyses Techniques

Cavitation is an essential problem that occurs in all kinds of pumps. This cavitation contributes highly towards the deterioration in the performance of the pump. In industrial applications, it is very vital to detect and decrease the effect of the cavitation in pumps. Using different techniques to analysis and diagnose cavitation leads to increase in the reliability of cavitation detection. The use of various techniques such as vibration and acoustic analyses can provide a more robust detection of cavitation within the pump. In this work therefore, focus is put on detecting and diagnosing the cavitation phenomenon within a centrifugal pump using vibration and acoustic techniques. The results obtained from vibration and acoustic signals in time and frequency domains were analysed in order to achieve better understanding regarding detection of cavitation within a pump. The effect of different operating conditions related to the cavitation was investigated in this work using different statistical features in time domain analysis (TDA). Moreover, Fast Fourier Transform (FFT) technique for frequency domain analysis (FDA) was also applied. Furthermore, the comparison and evaluation system among different techniques to find an adequate technique incorporating for accuracy and to increase the reliability of detection and diagnosing different levels of cavitation within a centrifugal pump were also investigated.

Improving impeller and water flow section of vane pumps

As a result of the research, it was found that the blades of the working impellers of the pumps are eroded at the inlet and outlet. Based on software studies, the points of erosion caused by cavitation and sand particles at the entrance of the impeller and the points of operation of the impeller under heavy load have been determined. The operating points under heavy load are compared with working impellers in nature. After comparison with software developments, it is determined that they are compatible with working impellers in natural conditions. The following impeller model is recommended to reduce cavitation and erosion processes in the impeller (Figures. 6, 10). The recommended impeller is shown in the inlet of the impeller to free water entry, prevent water shortage, and reduce the level of cavitation. (Figures 6, 10, 11). The ingress of water into the impeller is freed, the continuous movement of water is restored, and the methods of preventing the processes of decay and holes formed in the impeller are given. Recommended methods of significantly reducing the level of wear in the input and output parts of the impeller are given.

Characterization and monitoring of cavitation behavior induced by a dual-mode pulsed high-intensity focused ultrasound array

Pulsed high-intensity focused ultrasound (pHIFU) is capable of inducing cavitation in tissue without the need for contrast agents, thereby enhancing permeability and passive drug penetration in tissue with poor perfusion. We have developed and characterized the performance of a 64-element linear ultrasound array for image-guided therapy, capable of generating sufficient levels of inertial cavitation at 1 MHz, along with B-mode and Doppler imaging for targeting and cavitation assessment, respectively. Cavitation behaviors induced by different pHIFU exposures were investigated using high-speed imaging in agarose and polyacrylamide phantoms in conjunction with passive cavitation detection (PCD) and plane wave Doppler imaging. Image quality assessment was performed on in vivo porcine models, and cavitation monitoring was demonstrated on ex vivo tissues. High-speed images of the induced cavitation behavior while steering the beam focus both axially and laterally (within ±1.2 cm) were in agreement with Doppler power distributions and broadband noise emissions from PCD. Destructive cavitation behaviors in both gels and tissue were induced at relatively low peak-negative pressures (3–4 MPa), provided that the pHIFU focal waveform was nonlinearly distorted. B-mode image quality is sufficient for recognizing the relative position of anatomic landmarks and targeting cm-sized regions. [Work supported by NIH grants R01EB023910 and R01EB025187.]

Neurostimulation success rate of repetitive-pulse focused ultrasound in an in vivo giant axon model: An acoustic parametric study.

Focused ultrasound (FUS) is a promising tool to develop new modalities of therapeutic neurostimulation. The ability of FUS to stimulate the nervous system, in a noninvasive and spatiotemporally precise manner, has been demonstrated in animals and human subjects, but the underlying biomechanisms are not fully understood yet. The objective of the present study was to investigate the bioeffects involved in the generation of trains of action potentials (APs) by repetitive-pulse FUS stimuli in a simple invertebrate neural model. The respective influences of different acoustic parameters on the neurostimulation success rate (NSR), defined as the rate of FUS stimuli capable of evoking at least one AP, were explored using the system of afferent nerves and giant fibers of Lumbricus terrestris as neural model. Each parameter was studied independently by administering random FUS sequences while keeping all but one FUS parameter constant. The NSR was evaluated as a function of (i) the spatial-average pulse-average intensity (Isapa ); (ii) the pulse duration (PD); (iii) the pulse repetition frequency (PRF); iv) the number of cycles per pulse (Ncycles ); (v) two ultrasound frequencies, f0 =1.1MHz and f3 =3.3MHz, corresponding to the fundamental and third-harmonic resonant frequencies of the FUS transducer, respectively (spherical, radius of curvature: 50mm); and (vi) levels of emerging stable cavitation and inertial cavitation. The NSR associated to 1.1MHz repetitive-pulse FUS stimuli was found to increase as a function of increasing Isapa , PD, PRF, and Ncycles . When evaluating each parameter at f=1.1MHz, it was observed that NSRs close to 100% were achieved when sufficiently elevating their respective values. When computing the NSR as a function of the spatial-average, temporal-average intensity (Isata ), defined as the product of PRF, PD, and Isapa , a significant elevation of the NSR from 0% to close to 100% was measured by increasing Isata from values approximate to 4 W/cm2 to values higher than 12 W/cm2 . No clear and consistent trend was observed in trials aimed at exploring the effects of different levels of stable and inertial acoustic cavitation on the NSR. Finally, the feasibility of inducing neural responses with 3.3MHz repetitive-pulse FUS stimuli was also demonstrated with NSRs reaching up to 60%, in the range of FUS parameters studied. The time-averaged value of the radiation force per unit volume of tissue is proportional to the acoustic intensity. As a result, the observations from this study suggest that the neural structure responding to the stimulus is sensitive to the mean radiation force carried by the FUS sequence, regardless of the combination of FUS parameters giving rise to such force. The results from this study further revealed the existence of a minimal activation threshold with regard to Isapa .

Characterization of nonlinear field of a dual-mode linear array for image-guided applications of pulsed high-intensity focused ultrasound

Recent studies have shown that nonlinear pulsed high-intensity focused ultrasound (pHIFU) is capable of inducing cavitation, without the need for contrast agents, to enhance drug delivery in tissues with poor perfusion. Here, acoustic characterization of a dual-mode linear array designed for image-guided cavitation-enhanced drug delivery applications is performed. The array consists of 64 elements (1.07 MHz, 14.8 × 51.2 mm2, 0.8 mm pitch) and is controlled by an ultrasound system (V1 Verasonics) configured with an external power supply for pHIFU excitation. Acoustic holography measurement data were collected for varying focus position electronically steered in the transverse and axial directions and used for setting a boundary condition in the acoustic model. Nonlinear simulations of the array field are performed using the Westervelt equation at increasing power outputs of the array. Modelling results are validated by comparing with pressure waveforms measured in the focus using a fiber optic hydrophone. It is shown that the amplitude of the shock fronts formed at the focus increases for larger focusing angles of the field and is sufficient to maintain the therapeutic level of cavitation. Simulation results are in good agreement with the measurement data. [Work supported by NIH R01EB023910 and RSF 20-12-00145.]

수중방사소음 예측을 위한 빔형성 방법 기반 추진기 캐비테이션 음원준위 추정

In general, the prediction of underwater radiated noise requires source level information. This study proposes a method for the source level estimation of propeller cavitation based on the beamforming method. The proposed method obtains the source level information by determining the source strength corresponding to the estimated cavitation position. As the solution of the minimization problem can be determined analytically rather than numerically, it has the advantage of fast computational time. The proposed method is verified through a model-scale test conducted in a large cavitation tunnel of Korea Research Institute of Ships and Ocean Engineering. The estimated source level of the propeller cavitation matches well with a transfer-function-based method in the frequency band that satisfies the far-field. In addition, another method for reducing the computational time is considered through determining the source level from the cavitation position and sound pressure level.

Accelerating the Generation of Static Coupling Injection Maps Using a Data-Driven Emulator

<div class="section abstract"><div class="htmlview paragraph">Accurate modeling of the internal flow and spray characteristics in fuel injectors is a critical aspect of direct injection engine design. However, such high-fidelity computational fluid dynamics (CFD) models are often computationally expensive due to the requirement of resolving fine temporal and spatial scales. This paper addresses the computational bottleneck issue by proposing a machine learning-based emulator framework, which learns efficient surrogate models for spatiotemporal flow distributions relevant for static coupling injection maps, namely total void fraction, velocity, and mass, within a design space of interest. Different design points involving variations of needle lift, fuel viscosity, and level of non-condensable gas in the fuel were explored in this study. An interpretable Bayesian learning strategy was employed to understand the effect of the design parameters on the void fraction fields at the exit of the injector orifice. The results show a strong influence of the amount of non-condensable gas on the level of cavitation as well as the overall shape of the gas-phase structures at the orifice exit. The emulator framework involves the construction of deep autoencoders for efficient dimensionality reduction of the flowfields. Deep artificial neural networks were then employed for prediction of the flowfields for unknown operating conditions. The emulated flowfields were then tested by evaluating spray and combustion predictions from one-way coupling spray simulations. The analysis of the spray predictions from CFD-generated and emulator-predicted injections maps revealed that the emulation framework is capable of reproducing spray predictions with similar level of accuracy, yet at a fraction of the computational cost. The maximum achievable speed-up using the emulator framework is up to 2 million times over the traditional CFD approach for generating static coupling injection maps. The emulation framework provides an efficient pathway for integrating detailed injector simulations into spray and engine simulations.</div></div>

Assessing Fuel Property Effects on Cavitation and Erosion Propensity Using a Computational Fuel Screening Tool

Abstract To advance compression ignition combustion strategies, researchers have evaluated fuel property effects and their impact on achieving higher efficiencies and lower emissions levels relative to current capabilities. Within the Department of Energy's Co-Optima initiative, there has been a recent focus on understanding the influence of fuel properties on fuel injection performance. To help identify candidate fuels that can meet desired injector performance metrics, a computational fuel screening tool is under development that can link fuel properties with the tendency of a given fuel to cavitate and lead to cavitation-induced erosion. In the initial development of this tool, five liquid fuel properties were selected to represent candidate fuels, namely, density, viscosity, vapor pressure, surface tension, and heat of vaporization. A design of experiments methodology was used to generate a set of pseudofuel cases, which can represent the main effects and interactions among the fuel properties and be related to cavitation erosion predictions. Large eddy simulations were performed using a mixture modeling approach to predict the cavitation and erosion propensity of these pseudofuels in terms of the mean fuel vapor mole fraction and stored impact energy from repeated cloud collapse events. The low-order regression models generated from this study revealed the importance of liquid fuel density on cavitation formation, whereas liquid viscosity was found to have a strong negative correlation with erosion severity. The surrogate models were then used in the fuel screening tool to rank the cavitation and erosion tendency of four candidate single-component fuels: methyl decanoate, iso-octane, ethanol, and n-dodecane. While the fuel screening tool was not able to quantitatively predict the cavitation and erosion response metrics, the tool was able to accurately rank the relative cavitation and erosion propensity of the four fuels. Overall, ethanol and iso-octane were observed to produce the highest levels of cavitation and erosion, respectively.

In-nozzle flow and spray characteristics of large two-stroke marine diesel fuel injectors

To further increase efficiency as well as to reduce emissions of large two-stroke marine Diesel engines, the understanding of the fuel injection processes and the resulting spray atomization characteristics is of high importance. The sheer dimensions, the uniflow scavenging design with the central exhaust valve position and the high swirl motion of the charge air is imposing the need for peripheral multiple fuel injector arrangement. The two or three fuel injectors are arranged by 180° resp. 120° and hence, a strongly asymmetrical and eccentrical atomizer design is given as all of the typically five orifices face a similar direction which is defined by the injector position and swirl flow. Experiments have shown that these characteristic nozzle tip bore arrangements lead to a strong spray deflection due to inhomogeneous velocity profiles induced by cavitation inside the orifice. Specifically designed transparent nozzles have been utilized to qualitatively investigate the in-nozzle cavitation flow phenomena. Furthermore, the influence on the subsequent atomization behaviour by simultaneously acquiring the spray morphology has been studied. A simplified transparent one-hole nozzle was used with a matching nozzle tip geometry representative for a large two-stroke marine Diesel engine injector. Fuel pressures of 50 MPa were applied to meet engine realistic injection conditions. Moreover, different degrees of hydro-erosive grinding were applied to the orifices to investigate the effects on the spray morphology with decreasing levels of in-nozzle flow cavitation derived by increasing inlet radii between main nozzle tip bore and orifice.

Non-invasive ultrasonic modulation of visual evoked response by GABA delivery through the blood brain barrier

GABA is an inhibitory neurotransmitter that is maintained outside the brain by the blood brain barrier in normal condition. In this paper we demonstrate the feasibility of modulating brain activity in the visual cortex of non-human primates by transiently permeabilizing the blood brain barrier (BBB) using focused ultrasound (FUS) coupled with ultrasound contrast agents (UCA), followed by intra-venous injection of GABA. The visual evoked potentials exhibited a significant and GABA-dose-depend decrease in activity. The effect of the sonication only (with and without UCA) was also investigated and was shown to decrease the activity 8.7 times less than the GABA-induced inhibition enabled by BBB permeabilization. Finally, the UCA harmonic response was monitored during sonication to estimate the level of stable cavitation (a signature of the effectiveness of BBB permeabilization) and to avoid damage due to inertial cavitation (the sonication was automatically shut down when this condition was detected). Our results extend the promise of the exploration and treatment of the brain using non-invasive, controllable, repeatable, and reversible neuromodulation.

The secondary Bjerknes force between two oscillating bubbles in Kelvin-Voigt-type viscoelastic fluids driven by harmonic ultrasonic pressure

The interaction between two small bubbles experiencing transient cavitation in a nonlinear Kelvin-Voigt fluid is investigated. The time-delay effect in the interaction is incorporated in the coupled Keller-Miksis model. The refined model predicts that bubbles with radii smaller than 2μm will be repelled by large bubbles, in contrast to predictions from previous models. The matching pressure needed to obtain same level of transient cavitation in different Kelvin-Voigt fluids is shown to depend mainly on the shear modulus and is insensitive to other parameters, which makes it a useful parameter to correlate the results. When the radii of the bubbles fall between 4μm and 6μm, the secondary Bjerknes force obtained with matching pressures shows only weak dependence on the shear modulus. For the pressure amplitudes investigated, equilibrium distances can be found between two bubbles when the equilibrium radius of one of the bubbles is in a narrow range around 2 μm. The equilibrium distance decreases when the shear modulus is increased. A simple relation between the two quantities is established.

Recommended Procedures to Test the Resistance of Materials to Cavitation Erosion

Abstract Predicting cavitation erosion under full-scale operating conditions is difficult and relies on laboratory testing using accelerated methods such as ASTM G32-09, Standard Test Method for Cavitation Erosion Using Vibratory Apparatus, and ASTM G134-95, Standard Test Method for Erosion of Solid Materials by a Cavitating Liquid Jet. The main difficulty is that full-scale cavitation intensity is often unknown, and correlating cavitation field characteristics of the accelerated method and the full scale is not obvious. The problem is more acute for compliant polymeric coatings, used for protection or repair of parts subject to cavitation. Extensive testing of such materials shows that, unlike metallic surfaces, they are highly resistant to low-intensity cavitation but fail catastrophically when the intensity exceeds a certain threshold. Such behavior creates the risk of accepting a candidate coating for its resistance to cavitation if the coating was tested at a low cavitation intensity not representative of the application field conditions. This highlights the need to conduct tests with a range of cavitation intensities rather than a single intensity. This article uses results from extensive tests under various forms of cavitation to propose a generalized definition of cavitation intensity. It then presents data on the response of both metals and polymeric coatings to various levels of accelerated cavitation. A new method to test the coatings at varying cavitation intensities is then presented. Such tests provide maps of material resistance to different levels of cavitation and are helpful to make an informed decision. The tests also show that during cavitation exposure, the coatings are subjected not only to mechanical stress but also to significant heating, which dynamically modifies their properties during the exposure. Temperature rise in the coating when exposed to cavitation is directly connected to the cavitation intensity to which it is exposed, and this interaction needs to be considered.

Registration of the cavitation regime in liquids under the action of ultrasonic vibrations

Ultrasonic vibrations are widely used in various industries and production: in metallurgy, in the chemical and food industries, in mechanical engineering, and in medicine. This is due to the physicochemical changes in the substance when superimposed sound fields. Cavitation in the ultrasonic field causes dispersion and emulsification of certain substances, promotes coagulation and degassing, affects the processes of crystallization and dissolution, it is known that ultrasonic vibrations cause a variety of chemical transformations of the substance, including oxidation, reduction, polymerization and depolymerization reactions. The researchers find the explanation of these phenomena in the diverse effect of cavitation on matter: shock waves, micro streams, acoustic wind. The experiments were carried out in a liquid medium (un-distilled water). The volume of the experimental test was 10 dm3. To obtain ultrasonic vibrations, the method of magnetostriction was used, the principle of which is to convert electric oscillations into mechanical ones. To assess the cavitation regime, the level of cavitation was recorded in two stages: the degree of erosion of the artificial obstacle, the measurement of the intensity of the cavitation noise in the volume

Optimum Extraction of Algae-oil from Microalgae using Hydrodynamic Cavitation

Abstrac t - The production of microalgae biodiesel is one solution to solve the energy problem in the future, especially in the transportation sector. Some advantages of the development of the production of biodiesel from microalgae is high productivity, food security friendly and global warming problem-solving . The main problem in the production of microalgae biodiesel is the high production cost due to the high cost of lipid extraction. Several studies have been conducted to find a low cost extraction process. In this research, the Nannochloropsis sp. microalgae lipid extraction utilizing hydrodynamic cavitation has been studied. Effects of the concentration of solids, specific energy and time on the extraction have been examined. The study was conducted in a batch with a combined solvent of methanol and hexane. The influence of specific energy given at the same level of cavitation of increasing specific energy would increase the yield where it would be higher at the beginning and remain stable at the end of the process. At the same specific energy and level of cavitation, the value of concentration that provides the lowest extraction energy requirement was 0.105 g/g. The optimum of cavitation levels for the same specific energy and concentration at the value of cavitation number was 0.126. The optimum temperature for the extraction process was 42°C. The lowest extraction energy requirement was 16.743 MJ/kg lipid.

Determination of the cavity mode in the water

Ultrasonic oscillations find their wide application in various sectors and industries: metallurgy, chemical and food industries, in engineering, in medicine. This is due to physical and chemical changes when exposed to the sound field. Cavitation in ultrasonic field causes the dispersion and emulsification of certain substances and promotes coagulation and degassing affects of crystallization and dissolution. It is known that ultrasonic vibrations also cause a variety of chemical transformations of substances such as oxidation, recovery, polymerization, and depolymerization. Researchers of cavitation action on the matter find the explanation of these phenomena: shock waves and, consequently, acoustic wind. The experiments were conducted in liquid environment (non-distilled water). The volume of the experimental sample amounted to 10 dm3. Method of the magnetostriction was applied to receive ultrasonic vibration, the principle of which consists in transforming electrical oscillations into mechanical. The level of cavitation was checked in two stages to evaluate the cavitation mode according to the degree of erosion of the artificial barriers and to measure the intensity of cavitation noise in the volume.

Cavitation intensity monitoring in an axial flow pump based on vibration signals using multi-class support vector machine

The cavitation phenomenon, which is rampant in axial flow pumps, should be avoided due to its undesirable effects on the pump’s performance. Therefore, in this study the cavitation performance of an axial flow pump is monitored based on vibration signals. For this purpose, experimental vibration data is collected for five different levels of cavitation. Time-domain features are extracted based on statistical behavior of the measured signals. Considering the nonlinear and high-frequency nature of the cavitation noise in the signal, the second set of features including both time- and frequency-domain parameters are obtained based on statistical behavior of the first intrinsic mode function, via empirical mode decomposition combined with Hilbert Huang transform. Compensation distance evaluation technique is applied to pick the appropriate features. Multi-class support vector machine is trained for classification of the various levels of cavitation intensity. The results of testing the support vector machine algorithm show that the developed methodology can monitor the pump’s cavitation intensity in onsite operation with high accuracy.

Activation of microbubbles by low-intensity pulsed ultrasound enhances the cytotoxicity of curcumin involving apoptosis induction and cell motility inhibition in human breast cancer MDA-MB-231 cells

Ultrasound and microbubbles-mediated drug delivery has become a promising strategy to promote drug delivery and its therapeutic efficacy. The aim of this research was to assess the effects of microbubbles (MBs)-combined low-intensity pulsed ultrasound (LPUS) on the delivery and cytotoxicity of curcumin (Cur) to human breast cancer MDA-MB-231 cells. Under the experimental condition, MBs raised the level of acoustic cavitation and enhanced plasma membrane permeability; and cellular uptake of Cur was notably improved by LPUS–MBs treatment, aggravating Cur-induced MDA-MB-231 cells death. The combined treatment markedly caused more obvious changes of cell morphology, F-actin cytoskeleton damage and cell migration inhibition. Our results demonstrated that combination of MBs and LPUS may be an efficient strategy for improving anti-tumor effect of Cur, suggesting a potential effective method for antineoplastic therapy.