Cavitation Threshold Of Water Research Articles

Numerical modelling of acoustic cavitation threshold in water with non-condensable bubble nuclei

Numerical modelling of acoustic cavitation threshold in water is presented taking into account non-condensable bubble nuclei, which are composed of water vapor and non-condensable air. The cavitation bubble growth and collapse dynamics are modeled by solving the Rayleigh-Plesset or Keller-Miksis equation, which is combined with the energy equations for both the bubble and liquid domains, and directly evaluating the phase-change rate from the liquid and bubble side temperature gradients. The present work focuses on elucidating acoustic cavitation in water with a wide range of cavitation thresholds (0.02–30 MPa) reported in the literature. Computations for different nucleus sizes and acoustic frequencies are performed to investigate their effects on bubble growth and cavitation threshold. The numerical predictions are observed to be comparable to the experimental data in the previous works and show that the cavitation threshold in water has a wide range depending on the bubble nucleus size.

Modelling and measurement of laser-generated focused ultrasound: Can interventional transducers achieve therapeutic effects?

Laser-generated focused ultrasound (LGFU) transducers used for ultrasound therapy commonly have large diameters (6–15 mm), but smaller lateral dimensions (<4 mm) are required for interventional applications. To address the question of whether miniaturized LGFU transducers could generate sufficient pressure at the focus to enable therapeutic effects, a modelling and measurement study is performed. Measurements are carried out for both linear and nonlinear propagation for various illumination schemes and compared with the model. The model comprises several innovations. First, the model allows for radially varying acoustic input distributions on the surface of the LGFU transducer, which arise from the excitation light impinging on the curved transducer surfaces. This realistic representation of the source prevents the overestimation of the achievable pressures (shown here to be as high as 1.8 times). Second, an alternative inverse Gaussian illumination paradigm is proposed to achieve higher pressures; a 35% increase is observed in the measurements. Simulations show that LGFU transducers as small as 3.5 mm could generate sufficient peak negative pressures at the focus to exceed the cavitation threshold in water and blood. Transducers of this scale could be integrated with interventional devices, thereby opening new opportunities for therapeutic applications from inside the body.

An Analysis of Acoustic Cavitation Thresholds of Water Based on the Incubation Time Criterion Approach

Researchers are still working on the development of models that facilitate the accurate estimation of acoustic cavitation threshold. In this paper, we have analyzed the possibility of using the incubation time criterion to calculate the threshold of the onset of acoustic cavitation depending on the ultrasound frequency, hydrostatic pressure, and temperature of a liquid. This criterion has been successfully used by earlier studies to calculate the dynamic strength of solids and has recently been proposed in an adapted version for calculating the cavitation threshold. The analysis is carried out for various experimental data for water presented in the literature. Although the criterion assumes the use of macroparameters of a liquid, we also considered the possibility of taking into account the size of cavitation nuclei and its influence on the calculation result. We compared the results of cavitation threshold calculations done using the incubation time criterion of cavitation and the classical nucleation theory. Our results showed that the incubation time criterion more qualitatively models the results of experiments using only three parameters of the liquid. We then discussed a possible relationship between the parameters of the two approaches. The results of our study showed that the criterion under consideration has a good potential and can be conveniently used for applications where there are special requirements for ultrasound parameters, maximum negative pressure, and liquid temperature.

Acoustic Measurements of Nucleus Size Distribution at the Cavitation Threshold

An understanding of the acoustic cavitation threshold is essential for minimizing cavitation bio-effects in diagnostic ultrasound and for controlling cavitation-mediated tissue ablation in focused ultrasound procedures. The homogeneous cavitation threshold is an intrinsic material property of recognized importance to biomedical ultrasound as well as a variety of other applications requiring cavitation control. However, measurements of the acoustic cavitation threshold in water differ from those predicted by classic nucleation theories. This persistent discrepancy is explained by combining recently developed methods for acoustically nucleating single bubbles at threshold with numerical modeling to obtain a nucleus size distribution consistent with first-principles estimates for ion-stabilized nuclei. We identify acoustic cavitation at threshold as a reproducible subtype of heterogeneous cavitation with a characteristic nucleus size distribution. Knowledge of the nucleus size distribution could inspire new approaches to achieving cavitation control in water, tissue and a variety of other media.

Shock Propagation Effects in Multilayer Assembly Including a Liquid Phase

During a ballistic impact, the protective material that plays the role of armour has to dissipate the kinetic energy in order to limit the projectile penetration in the target. Our aim is to emphasis on the role played by a liquid-filled system on the impact energy mitigation due to cavitation inception and later bubble expansion. To observe this, small scale experiments have been carried out on a three layers sample (Aluminium-Water-PMMA) submitted to shock waves induced by laser impact applied on the Al face. Rapid camera visualizations allow reproducing, at small scale, the effects of projectiles on armours for various monitored impact energies. We observe the formation of bubbles for sufficiently intense impacts due to traction effects in the water caused by the multiple reflections of waves within the sample. The cavitation threshold of water under dynamic loading is then experimentally investigated for two samples: one with 600 μm thick Al / 400 μm of water and 3 mm of PMMA, the other with 1000 μm thick Al / 1600 μm of water and 3 mm of PMMA. Using dimensional analysis, we show that the energy taken during the process of inception and bubble expansion becomes more important as the energy of the impact increases.

Enhanced antimicrobial effect of ultrasound by the food colorant Erythrosin B

The synergistic combination of the food colorant Erythrosin B (E-B, FD&C 3) (0, 25, and 50μM) and low-frequency ultrasound (20kHz, 0.86–0.90WmL−1) was evaluated against Listeria innocua. Although E-B was antibacterial by itself, the inactivation rate significantly increased in a concentration-dependent manner upon exposure to ultrasound and followed a sigmoidal behavior. The enhanced antimicrobial effect of E-B in the presence of ultrasound can be explained in part from a microbubble disappearance study in which it was confirmed that the presence of E-B enhances inertial cavitation, thereby enhancing the antimicrobial effect of ultrasound. The inactivation rate in a sequential treatment, where L. innocua was sonicated for 4min followed by exposure to 25μM Erythrosin B, was comparable to that obtained by the simultaneous treatment, indicating complementary mechanisms of inactivation. Fluorescence microscopy showed attachment of E-B to the cells, which may explain its intrinsic antimicrobial property. Other mechanism may include the confirmed decrease in the cavitation threshold of water by addition of E-B, resulting in more effective cavitation. The study offers a proof-of-concept of a novel approach to complement ultrasound treatment for enhanced microbial inactivation.

The mechanical index and bubbles in tissue, an evidentiary review

The mechanical index (MI) quantifies the likelihood that diagnostic ultrasound will produce an adverse biological effect by a non-thermal mechanism. The current formulation of the MI is based on inertial cavitation thresholds in water and blood as calculated for a pulse duration of one period. However, tissue is not a liquid but a viscoelastic solid, and imaging pulses may be much longer. The importance of these differences has been quantified using the Gilmore equation for water and blood and a form of the Keller-Miksis equation modified for soft tissue. It is shown that the threshold for cavitation is higher in soft tissues, and much higher in muscle, than in blood. Experimentally determined thresholds in tissue lie above these theoretical results by up to an order of magnitude. This suggests that use of the MI as part of the FDA 501(k) approval process may unnecessarily restrict the outputs of diagnostic ultrasound machines. Additionally, a simple analysis of another potential mechanism for biological effects, radiation force, indicates that the very form of the MI does not include all non-thermal mechanisms but, perhaps, only one. These results cast doubt on the value of the MI as a reliable means of assessing patient safety.

Inertial cavitation threshold dependence on high static pressures.

The creation of a bubble in a liquid is energetically favorable when the liquid is subject to a net/an overall tension less than of its saturated vapor pressure. This gain is offset by the creation of a liquid-vapor/gas interface, and only bubbles larger than some critical size will spontaneously grow. The magnitude of the acoustic pressure required to produce a cavity of the critical size is termed the cavitation threshold of the liquid. The dependence of the cavitation threshold on hydrostatic pressure has previously been reported up to 130 bars in terms of electrical power applied to the acoustic driving transducer. These measurements used a standing wave set-up in a stainless steel spherical resonator (24.1 cm outer diameter, 1.9 cm thick) with a Q &amp;gt; 10 000 when fluid loaded. This work will extend into higher pressure regimes and will be used to extrapolate the cavitation threshold at 1 kbar.

Enhancement of Drug Delivery in Tumors by Using Interaction of Nanoparticles with Ultrasound Radiation

Efficacy and safety of cancer chemo- and biotherapy are limited by poor penetration of anti-cancer drugs from blood into tumor cells. Tumor blood vessel wall, slow diffusion in the interstitium, and cancer cell membrane create physiological barriers for anti-cancer drugs, in particular promising macromolecular agents. Recently, we proposed to use selective accumulation of exogenous nano- and microparticles in tumors followed by ultrasound-induced cavitation for safe and efficient drug and gene delivery. In this paper, we first investigated the influence of polystyrene nanoparticles (100 and 280 nm in diameter and concentration up to 0.2% w/w) on cavitation threshold in water at the frequency of 20 kHz. Then, using optimal irradiation parameters found in the first part of this work, we studied efficacy of cancer chemotherapy with this technique. The experiments were performed in athymic nude mice bearing human colon KM20 tumors, which are highly resistant to chemotherapy. Ultrasound with the frequency of 20 kHz in combination with i.v. injected polystyrene nanoparticles was applied to enhance delivery of chemotherapeutic agent 5-fluorouracil. Our studies demonstrated that ultrasound irradiation in combination with the nanoparticle and drug injections significantly decreased tumor volume and resulted in complete tumor regression at optimal irradiation conditions, while the volume of control (non-irradiated) tumors increased despite drug injections. These data suggest that ultrasound-induced drug delivery may improve efficacy of current cancer treatment regimens.

Applying spectrum analysis and cepstrum analysis to examine the cavitation threshold in water and in salt solution

The paper presents the way of determining the cavitation threshold by means of classical spectral analysis and proposes the usage of cepstrum analysis in examining the cavitation phenomenon. Cepstrum analysis enables a more lucid interpretation of signals generated in the cavitation process than the universally used Fourier analysis. This refers above all to evaluating the relationship between particular frequencies as well as frequency groups. The research conducted allowed us to observe the changes of spectrum near the cavitation threshold in water, in water partly degassed and in salt solution in the free field and in the standing wave field. Differences of spectrum structure for particular cases were noted, especially for the third harmonic and the first subharmonic. The measurements done in the standing wave field showed differences in spectrum, depending on whether the measurements were done in the loop or in the node of the wave. In particular, what was not observed was the occurrence of subharmonics with a frequency two times lower than the basic frequency which were typical of the free field. Other characteristic spectrum elements that could unmistakably point to reaching the cavitation threshold were not noticed either. The cepstrum analysis proved the existence of irregularities, hardly visible in the classical Fourier spectrum. This refers especially the range below the signal’s basic frequency.

Applications of the compensating pressure theory of water transport

Some predictions of the recently proposed theory of long-distance water transport in plants (the Compensating Pressure Theory) have been verified experimentally in sunflower leaves. The xylem sap cavitates early in the day under quite small water stress, and the compensating pressure P (applied as the tissue pressure of turgid cells) pushes water into embolized vessels, refilling them during active transpiration. The water potential, as measured by the pressure chamber or psychrometer, is not a measure of the pressure in the xylem, but (as predicted by the theory) a measure of the compensating pressure P. As transpiration increases, P is increased to provide more rapid embolism repair. In many leaf petioles this increase in P is achieved by the hydrolysis of starch in the starch sheath to soluble sugars. At night P falls as starch is reformed. A hypothesis is proposed to explain these observations by pressure-driven reverse osmosis of water from the ground parenchyma of the petiole. Similar processes occur in roots and are manifested as root pressure. The theory requires a pump to transfer water from the soil into the root xylem. A mechanism is proposed by which this pump may function, in which the endodermis acts as a one-way valve and a pressure-confining barrier. Rays and xylem parenchyma of wood act like the xylem parenchyma of petioles and roots to repair embolisms in trees. The postulated root pump permits a re-appraisal of the work done by evaporation during transpiration, leading to the proposal that in tall trees there is no hydrostatic gradient to be overcome in lifting water. Some published observations are re-interpreted in terms of the theory: doubt is cast on the validity of measurements of hydraulic conductance of wood; vulnerability curves are found not to measure the cavitation threshold of water in the xylem, but the osmotic pressure of the xylem parenchyma; if measures of xylem pressure and of hydraulic conductance are both suspect, the accepted view of the hydraulic architecture of trees needs drastic revision; observations that xylem feeding insects feed faster as the water potential becomes more negative are in accord with the theory; tyloses, which have been shown to form in vessels especially vulnerable to cavitation, are seen as necessary for the maintenance of P, and to conserve the supplementary refilling water. Far from being a metastable system on the edge of disaster, the water transport system of the xylem is ultrastable: robust and self-sustaining in response to many kinds of stress.

Negative Pressure Generated by Octopus Suckers: A Study of the Tensile Strength of Water in Nature

ABSTRACT The decrease in hydrostatic pressure generated by octopus suckers adhering to wettable and non-wettable surfaces was measured using a flush-mounted miniature pressure transducer. The cavitation thresholds, or lowest sustainable pressures, of sea water on the same surfaces were also measured and were compared with the pressures generated by octopuses. It is shown that suckers can generate hydrostatic pressures below 0MPa on moderately wettable surfaces. This disproves the commonly repeated assumption that suckers cannot produce pressures below a vacuum and suggests that the importance of suction in attachment mechanisms may have been overlooked. On epoxy, the lowest recorded pressure was —0.168MPa (0.268MPa or 2.66atm below ambient), and the octopus generated negative pressure in 35 % of the pulls that were considered maximal efforts. The suckers never generated negative pressures on non-wettable surfaces. These results are in agreement with the range of pressures that sea water can sustain on the same surfaces. It is suggested, therefore, that cavitation, the failure of water in tension, limits the attachment force of suckers. The difference between the cavitation threshold of water in nature and the cavitation threshold of pure water is discussed.

The past, present, and future of acoustic cavitation nucleation

Those familiar with the field do not need to be reminded that acoustic cavitation is the cornerstone of sonoluminescence and sonochemistry. However, an equally important and often overlooked statement is that nucleation is the cornerstone of acoustic cavitation. So critical is the nature of the nucleus to the cavitation process that the acoustic cavitation threshold in water can be varied from a few atmospheres to a few hundred atmospheres just by altering the distribution and properties of the nuclei. (The acoustic cavitation threshold is the maximum acoustic pressure amplitude to which a liquid can be exposed before cavitation inception.) The fundamentals of acoustic cavitation nucleation will be presented in this paper, which is intended to be tutorial in nature. Topics include homogeneous and heterogeneous nucleation, stabilization mechanisms, models of heterogeneous cavitation nuclei, and the dependence of the cavitation threshold on the properties of the nucleus. [Work supported by ONR and the NPS Res. Program]

Thresholds for transient cavitation produced by pulsed ultrasound in a controlled nuclei environment

Transient cavitation is a discrete phenomenon that relies on the existence of stabilized nuclei, or pockets of gas within a host fluid, for its genesis. A convenient descriptor for assessing the likelihood of transient cavitation is the threshold pressure, or the minimum acoustic pressure necessary to initiate bubble growth and subsequent collapse. An automated experimental apparatus has been developed to determine thresholds for cavitation produced in a fluid by short tone bursts of ultrasound at 0.76, 0.99, and 2.30 MHz. A fluid jet was used to convect potential cavitation nuclei through the focal region of the insonifying transducer. Potential nuclei tested include 1-microns polystyrene spheres, microbubbles in the 1- to 10-microns range that are stabilized with human serum albumin, and whole blood constituents. Cavitation was detected by a passive acoustical technique that is sensitive to sound scattered from cavitation bubbles. Measurements of the transient cavitation threshold in water, in a fluid of higher viscosity, and in diluted whole blood are presented. These experimental measurements of cavitation thresholds elucidate the importance of ultrasound, host fluid, and nuclei parameters in determining these thresholds. These results are interpreted in the context of an approximate analytical theory for the prediction of the onset of cavitation.

Cavitation threshold measurements for microsecond length pulses of ultrasound.

The acoustic cavitation threshold of an aqueous solution has been measured at megahertz frequencies as a function of pulse width and pulse repetition frequency for various combinations of these quantities. The fluid tested was a 0.1M KOH-H3BO3 buffer solution with pH 10.9, which contained luminol, was saturated with argon, and filtered to 25 mu. The presence of cavitation was detected by a photomultiplier tube that required the emission of visible light that was both larger in magnitude and longer in duration than a preset criterion. It was observed that the cavitation threshold of water under pulse conditions decreases both when the pulse width is fixed and the pulse repetition frequency is increased, and when the pulse repetition frequency is fixed and the pulse width is increased. Acoustic cavitation thresholds measured in aqueous solutions are significantly less than those acoustic pressures associated with instruments that are currently in widespread use in medicine.

Effect of Dilute Polymer Additives on the Acoustic Cavitation Threshold of Water

Measurements are presented of the variation of the acoustic cavitation threshold of water with concentration of the polymer additives polyethylene oxide and guar gum. It was found that small amounts of these additives could significantly increase the cavitation threshold. A theoretical model, based upon nucleation of a gas bubble from a Harvey-type crevice in a mote or solid particle, is developed that gives good agreement with the measurements. The applicability of this approach to an explanation of cavitation index reduction in flow-generated or confined jet cavitation, when polymer additives are introduced, is discussed.

EXPERIMENTAL INVESTIGATION ON NONLINEAR REFLECTION OF SHORT IMPULSIVE UNDERWATER SOUND AT WATER SURFACE

The nonlinear phenomena in the vicinity of free surface of water, induced by the incidence of high intensity underwater compressional pulse, are experimentally investigated. The behaviors of cavitation bubbles and water surface are observed by photographical visualization. It is concluded that the transmission and the reflection at the free surface are linear, and the limitation of negative pressure observed in the reflected pulse must be due to the onset of cavitation. Utilizing the phenomena, the cavitation threshold of water for negative pressure pulse of about 10 µs duration is measured. Obtained threshold value of air-saturated tap water is about 10 atm., and after water is degassified to 20% of saturation it becomes about 20atm., at 20°C. The dependence of the threshold on temperature is also investigated.

Effect of Surface Tension on the Cavitation Threshold of Water

The threshold for transient cavitation in degassed water has been measured in a stationary wave system as a function of surface tension. A surfactant was used to vary the surface tension of water from approximately 70 to 30 dyn/cm2. The cavitation threshold was found to vary inversely with the surface tension in disagreement with the theoretical predictions of Apfel [J. Acoust. Soc. Amer. 48, 1179–1186 (1970)]. Glass capillary tubes were used to construct macroscopic models of microscopic crevices thought to nucleate cavitation. The crevices were coated with polystyrene in order to obtain a nonwettable surface. Measurements made of the receding contact angle of an air-water interface moving in the model crevice showed a critical dependence of the contact angle upon surface tension. Motion pictures will be shown of the receding contact angle as a function of surface tension and how this receding interface may nucleate cavitation. If an empirical relationship is made between the contact angle and the surface tension, and this empirical dependence used in Apfel's theory, then good agreement is obtained between theory and experiment. [Work supported by the Office of Naval Research and the Naval Academy Research Council.]

Thresholds of Acoustic Cavitation in Water

Cavitation thresholds in water have been measured as a function of frequency, dissolved gas, ambient pressure, and suspended-particle size. The apparatus used comprises a 2-1 volume of water enclosed by a spherical glass shell driven at its radially symmetric resonance frequencies by 8 multiresonant piezoelectric transducers. Large acoustic pressures can be produced, ranging from 10 bar at 27 kc/sec to 200 bar at 1.16 Mc/sec. The threshold data can be divided into three regions: In region A—defined by f&amp;lt;200 kc/sec, acoustic pressure Pa&amp;lt;3 bar, and air saturation presure Ps&amp;gt;600 mm Hg—small air bubbles grow by rectified diffusion and stabilize at the pressure nodes. In region B—defined by f&amp;lt;200 kc/sec, Pa&amp;gt;3 bar, and Ps&amp;lt;500 mm Hg—transient cavities are formed that can be detected visually and aurally. In region C—where f&amp;gt;200 kc/sec, Pa&amp;gt;5 bar, for any value of Ps—transient cavities are formed, but their presence can be detected acoustically only. The threshold tends to a slope of 12 dB/octave for frequencies above 1 Mc/sec. Experiments on cavitation at pressures larger than the threshold indicate that only a finite number of cavitation events can be produced in a given sample of water when it is isolated from contamination by airborne motes. In this way, water can be “strengthened” by a factor of at least 8 by repeated cavitation.

Ultrasonic Cavitation Thresholds in Water

The temperature dependence of the minimum sound pressure needed to produce cavitation in gassy water has been measured over a range of 0 to 30°C. Both plane progressive and focused waves of frequency one megacycle per second were used. The cavitation pressure threshold Pc is not a linear function of temperature, and increases by a factor of 2.5 between 30 and 0°C. About 50 percent higher sound-pressure amplitude is needed to initiate cavitation than to maintain it. The relation of Pc to the reciprocal temperature, to viscosity, and to the degree of undersaturation is discussed.