Cavitation Pressure Research Articles

Testing hypotheses that link wood anatomy to cavitation resistance and hydraulic conductivity in the genus Acer

• Vulnerability to cavitation and conductive efficiency depend on xylem anatomy. We tested a large range of structure-function hypotheses, some for the first time, within a single genus to minimize phylogenetic 'noise' and maximize detection of functionally relevant variation. • This integrative study combined in-depth anatomical observations using light, scanning and transmission electron microscopy of seven Acer taxa, and compared these observations with empirical measures of xylem hydraulics. • Our results reveal a 2 MPa range in species' mean cavitation pressure (MCP). MCP was strongly correlated with intervessel pit structure (membrane thickness and porosity, chamber depth), weakly correlated with pit number per vessel, and not related to pit area per vessel. At the tissue level, there was a strong correlation between MCP and mechanical strength parameters, and some of the first evidence is provided for the functional significance of vessel grouping and thickenings on inner vessel walls. In addition, a strong trade-off was observed between xylem-specific conductivity and MCP. Vessel length and intervessel wall characteristics were implicated in this safety-efficiency trade-off. • Cavitation resistance and hydraulic conductivity in Acer appear to be controlled by a very complex interaction between tissue, vessel network and pit characteristics.

Numerical study of cavitation on the surface of the guide vane in three gorges hydropower unit

Large-area erosions such as rust and obvious cavitation were found on the surface of the guide vane in Three Gorges hydropower units. A numerical explanation of the cavitation is given in this article. At first, based on the characteristic performance curves of the prototype hydro-turbine supplied by ALSTOM together with the actual operating conditions, an operating point is chosen for numerical analysis using the Reynolds-Averaged Navier-Stokes (RANS) equations. The flow passages from the inlet of the spiral case to the outlet of the draft tube are included in the computational domain. The results show that the static pressure on the guide vane surface is much higher than the critical pressure of cavitation. Secondly, a tiny protrusion on the guide vane surface is considered and the problem is simplified to a 2-D problem to study the local detailed flow near the guide vane surface. The protrusion is 0.5 mm in height and is 5.0 mm in width. On the basis of the results of RANS simulations, the 2-D problem is studied using the Large Eddy Simulation (LES). It is shown that there exists a region in which the static pressure reaches a level below the vapor pressure of the water. Thirdly, a cavitation model is included for the 0.5 mm protrusion case and another tiny pit case, with a tiny pit 0.3 mm in depth and 1.0 mm in width. The results show that vapor bubble exists at the protrusion entrance and the pit exit as the low pressure regions.

Estimation of Deep Penetration Resistance with Spherical Specific Cavitation Energy

A simple model is suggested for deep penetration resistance of rigid, axially-symmetric, nose-pointed projectiles penetrating ductile metal targets. Model is based on power balance between the power supplied by the projectile during steady-state penetration and elastoplastic power needed for expanding penetration hole. The latter is approximated with the aid of the spherical specific cavitation energy (spherical cavitation pressure). Frictionless model includes an empirical parameter which is found to be practically independent of target material characteristics but reflects the shape of head profile. For ogival nose projectiles (with the spherical nose as a special case) the empirical parameter values are limited to a narrow range, slightly lower than one. Friction resistance is included by the Prandtl friction model leading to a general expression for the deep penetration hardness. Experimental data of spherical and ogival nose projectiles penetrating aluminium targets is compared with analytical predictions for penetration depth and an optimal ogival nose projectile is discussed.

Negative pressure cavitation extraction and antioxidant activity of genistein and genistin from the roots of pigeon pea [ Cajanus cajan (L.) Millsp.

A new method—negative pressure cavitation extraction (NPCE) was proposed and investigated for the extraction of the main isoflavonoids, namely genistein and genistin from pigeon pea roots. The effects of extraction time and particle size on the extraction yields were firstly optimized, then a central composite design (CCD) combined with response surface methodology (RSM) was used to study the effects of negative pressure, ethanol concentration and liquid/solid ratio on the extraction yields. The maximum extraction yields of genistein and genistin reached 0.418 and 0.398 mg/g, respectively, under the optimal conditions: extraction time 45 min, particle size 50 mesh, negative pressure −0.05 MPa, ethanol concentration 70% and liquid/solid ratio 44:1. Furthermore, the antioxidant activity of NPCE extract was assessed by 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical-scavenging assay. NPCE extract possessed notable concentration-dependent antioxidant activity with IC 50 value of 0.062 mg/ml.

Ballistic Limit Predictions with Quasi-Static Cavitation Fields

Recent work on ductile hole enlargement under plane-stress conditions has revealed that while the internal pressure does not reach a saturation level, the energy increment required to create a nominal hole volume increment admits a finite asymptotic value. This specific cavitation energy, which is identified with the cavitation pressure required for plane-strain and spherical cavitation patterns, suggests a possible new view of cavitation states in energetic terms. Based on the specific cavitation energy the ballistic limits of monolithic targets are estimated from a simple energy balance and residual velocities are found from the Recht-Ipson formula. This plate perforation model is independent of projectile head profile and neglects friction. Albeit the simplicity, comparison with experimental and numerical data from various sources, for conical and ogival-nose projectiles, shows good agreement. In fact, over a practical range of h/ D ratio, residual velocities are bounded between plane-stress and plane-strain predictions, gradually shifting from plane-stress limit to plane-strain bound as h/ D increases. Spherical cavitation fields are also discussed in conjunction with limits of validity of cavity expansion models and connection between plane-stress cavitation and the ultimate tensile stress is demonstrated.

The Effects of Negative Pressure Cavitation Method (NPC) on Adsorption of Heavy Metals Solution by <i>Candida utilis</i>

In this study, a new method (negative pressure cavitation method, NPC) for metal ions removal from industry waste water has been studied. Under the identical adsorption conditions，we have seen some different effects among static adsorption, shaking adsorption and NPC adsorption. The results are as following: four kind metal ions showed the accordant phenomenon that the sequence of adsorption capacity is NPC adsorption>shaking adsorption>static adsorption. The different metal ions have different improvement of removal ratio. The sequence is Cd>Hg>Pb>Cu. The intercellular pH of absorbed yeast cells increased with the adsorption process from acidic to alkaline. These may suggest that the Candida utilis has certain resistance against heavy metals. The increased pH is also an environment stress response of Candida utilis. So NPC adsorption may have potential values to removal of metal ions.

Enhanced extraction of astragalosides from Radix Astragali by negative pressure cavitation-accelerated enzyme pretreatment

The optimal conditions for extraction of astragalosides III and IV (AGs III and IV) in Radix Astragali by negative pressure cavitation-accelerated enzyme pretreatment were studied on the basis of a Box–Behnken design and response surface methodology. Experimental results showed that negative pressure, amount of enzyme and incubation temperature were the main factors governing the enzyme pretreatment of Radix Astragali. The optimum parameters were obtained as follows: negative pressure −0.08 Mpa, amount of enzyme 1.48% (w/w of materials) and incubation temperature 45 °C. Under the optimal conditions, the maximal extraction yields of AGs III and IV were 0.103 and 0.325 mg/g, which were 41.67% and 65.31% increased as compared to those without enzyme pretreatment, respectively. The effect of negative pressure cavitation and enzyme pretreatment on the structural changes of plant cells was observed by scanning electron microscopy. In conclusion, negative pressure cavitation-accelerated enzyme pretreatment was proved to be environment-friendly and economical, and could be used in secondary metabolites production.

Improved identification of squeeze-film damper models for aeroengine vibration analysis

Numerical solution of the Reynolds equation imposes a prohibitive computational cost on the dynamic analysis of practical squeeze film damped turbomachinery. To surmount this problem, the present paper develops the use of Chebyshev polynomial fits to identify finite difference (FD) solution of the incompressible Reynolds equation. The proposed method manipulates the Reynolds equation to allow efficient and accurate identification in the presence of cavitation, the feed-groove, feed-ports, end-plate seals and supply pressure. The ability of Chebyshev polynomials to rapidly reproduce FD routines is demonstrated. The bearing models developed are experimentally proven to give more accurate results than alternative analytical bearing models.

Cavitation in Metastable Liquid Nitrogen Confined to Nanoscale Pores

We studied cavitation in metastable fluids drawing on the example of liquid nitrogen confined to spheroidal pores of specially prepared well-characterized mesoporous silica materials with mean pore diameters ranging from approximately 6 to approximately 35 nm. Cavitation was monitored in the process of evaporation/desorption from fully saturated samples with gradually decreasing vapor pressure at the isothermal conditions. The onset of cavitation was displayed by a sharp step on the desorption isotherm. We found that the vapor pressure at the onset of cavitation depended on the pore size for the samples with pores smaller than approximately 11 nm and remained practically unchanged for the samples with larger pores. We suggest that the observed independence of the cavitation pressure on the size of confinement indicates that the conditions of bubble nucleation in pores larger than approximately 11 nm approach the nucleation conditions in the bulk metastable liquid. To test this hypothesis and to evaluate the nucleation barriers, we performed grand canonical and gauge cell Monte Carlo simulations of nitrogen adsorption and desorption in spherical silica pores ranging from 5.5 to 10 nm in diameter. Simulated and experimental adsorption isotherms were in good agreement. Exploiting the correlation between the experimental cavitation pressure and the simulated nucleation barrier, we found that the nucleation barrier increased almost linearly from approximately 40 to approximately 70 k(B)T in the range of pores from approximately 6 to approximately 11 nm, and varied in diapason of 70-75 k(B)T in larger pores, up to 35 nm. We constructed the dependence of the nucleation barrier on the vapor pressure, which asymptotically approaches the predictions of the classical nucleation theory for the metastable bulk liquid at larger relative pressures (>0.6). Our findings suggest that there is a limit to the influence of the confinement on the onset of cavitation, and thus, cavitation of nanoconfined fluids may be employed to explore cavitation in macroscopic systems.

0410 キャビテーションにおけるクラウド発生・消滅挙動の観察とその定量化画像解析(OS4-2 キャビテーションおよびマイクロバブル効果とその応用技術,オーガナイズドセッション)

There are many observations of cavitating flow using a high-speed video camera. They give us instantaneous and spatial images of cavitation clouds and surrounding small bubble behavior. In this study, we show some cavitation clouds behaviors using a high-speed video camera with an image analysis in order to estimate the behavior quantitatively. Especially, We show good advantages of frame difference method to analyze the behavior related to cavitating flow with small bubbles: e.g. growing and collapsing behavior of cavitation clouds and pressure wave propagation.

Determination of paclitaxel and its analogues in the needles of Taxus species by using negative pressure cavitation extraction followed by HPLC‐MS‐MS

A new separation method, negative pressure cavitation (NPC) extraction followed by HPLC-MS-MS for the determination of paclitaxel and its analogues in the needles of Taxus species is described in this study. Compared with three conventional extraction methods, NPC is a more effective, economical, and facile method for the separation of nature compounds from herbal plants. In contrast to high-temperature extraction, NPC at low temperature can minimize undesirable reactions such as thermal decomposition or degradation. In addition, the extraction mechanism of NPC was also illuminated. The effects of vacuum degree, extraction solvent, ratio of solid to liquid, time, and times extraction were studied and optimized. The optimum extraction conditions were as follows: vacuum degree -0.03 MPa, solvent 80% v/v alcohol, ratio of material to liquid 1:15 (g/mL), extraction time 60 min, extraction (x3). Using these conditions, the recoveries of 10-deacetyl-7-xylosylpaclitaxel, 10-deacetylpaclitaxel, cephalomannine, and paclitaxel were higher than 95.88, 95.82, 94.85, and 96.18%, respectively. The contents of paclitaxel, 10-deacetyl-7-xylosylpaclitaxel, 10-deacetylpaclitaxel, and cephalomannine for Taxus chinensis were 0.0053, 0.0467, 0.0132, and 0.0076%, and 0.0067, 0.0153, 0.0047, and 0.0064% for Taxus cuspidata, respectively. Furthermore, a comparison of SEM images observed the morphological changes of microstructures and cellular damage in yew needles.

Cavitation, aeration and negative pressures in siphonic roof drainage systems

The main purpose of this study was to examine negative pressures in siphonic downpipes and to see whether these can be controlled through breaking the siphonic action by injecting air at certain points in a vertical downpipe. The study also investigated cavitation and its propagation through a prototype scale siphonic system. The paper presents methods for limiting the minimum pressure in siphonic downpipes in tall buildings. A distinctive drop in pressure between approximately —70 kN/m2 and —96 kN/m2 occurred in a 80 mm diameter downpipe and it was not possible to sustain pressures between these limits. The pressure drop to -96 kN/m2 caused the formation of a distinctive cavitation zone. Any increase in downpipe length, beyond the cavitation zone, produced a proportional increase in the cavitation zone length. Practical application: Cavitation is perceived to be a serious problem for designers of siphonic drainage systems to be installed in tall buildings. Using full-scale testing this paper provides evidence that in practice cavitation in plastic downpipes is unlikely to cause damage. The paper also provides guidelines for maximum spacing of air inlets to limit the minimum pressure to ∼70 kN/m 2 below atmospheric pressure without significantly decreasing the system capacity.

Testing the 'rare pit' hypothesis for xylem cavitation resistance in three species of Acer.

Eudicot angiosperms with greater vulnerability to xylem cavitation tend to have vessels with greater total area of inter-vessel pits, which inspired the 'rare pit' hypothesis: the more pits per vessel, by chance the leakier will be the vessel's single air-seeding pit and the lower the air-seeding threshold for cavitation to spread between vessels. Here, we demonstrate the feasibility of the hypothesis, using probability theory to model the axial propagation of air through air-injected stems. In the presence of rare, leaky pits, air-seeding pressures through short stems with few vessel ends in series should be low; pressures should increase in longer stems as more end-walls must be breached. Measurements on three Acer species conformed closely to model predictions, confirming the rare presence of leaky pits. The model indicated that pits air-seeding at or below the mean cavitation pressure (MCP) occurred at similarly low frequencies in all species. Average end-wall air-seeding pressures predicted by the model closely matched species' MCPs. Differences in species' vulnerability were primarily attributed to differences in frequency of the leakiest pits rather than pit number or area per vessel. Adjustments in membrane properties and extent of pitting per vessel apparently combine to influence cavitation resistance across species.

Two-bubble interaction under the sound field

The paper established the motion equation of two-bubble walls under the sound field, and obtained the resonant frequency, vibration radius and radiation pressure of the double-bubble cavitation. From the frequency equation, radius of vibration and sound pressure equation we can see that the movement of two-bubble is different from a single bubble. Resonance frequency, resonance amplitude and radiation pressure are related to the distance between the bubble. By carrying out the numerical solution by MATLAB, we found that the resonance frequency and amplitude resonance increased with the distance between the two-bubble.

373 ピストンスラップによる冷却水内圧力変動とライナキャビテーションに関する研究

373 ピストンスラップによる冷却水内圧力変動とライナキャビテーションに関する研究

Deep penetration analysis with dynamic cylindrical cavitation fields

Dynamic cylindrical cavitation fields are studied for a family of plastic orthotropic solids with arbitrary strain hardening response. Analysis is within the framework of plane-strain, steady state flow theory of associated plasticity. New formulae for cavitation pressure are validated against accurate numerical analysis and contact is made with existing studies. A uniform procedure is presented for estimating penetration depth of rigid axisymmetric projectiles at normal impact. Comparison with available experimental data reveals a very good agreement for both spherical and cylindrical dynamic cavitation models. Quasi-static cavitation pressure formulae can predict penetration depth with an appropriate scaling of the yield stress. The scaling factors appear to be independent of material properties but reflect the shape of head profile.

Decisive influence of the ionization strength of cosmic rays on the cavitation characteristics of pure water

The experiment result in this article shows that the initial and critical cavitation pressure of pure water are both increasing along with the increase of height above sea level, and the ionization strength of cosmic rays in the lower aerosphere is the crucial factor which influences the cavitation pressure of pure water. The author concludes the relationship between the cavitaion pressure of pure water and the height above sea level. Moreover, air particles in water caused by the radiation of cosmic rays can exist in the water for a long time and will not escape.

CFD Modeling of a Thermal and Shear-Thinning Elastohydrodynamic Line Contact

In this paper a computational fluid dynamics (CFD) approach for solving elastohydrodynamic lubrication using the freely available package OPENFOAM is introduced. The full Navier–Stokes equations are solved, which enables the entire flow domain to be modeled and all gradients inside the lubricated contact to be resolved. The phenomenon of cavitation is taken into account by employing a homogenous equilibrium cavitation model, which maintains a specified cavitation pressure inside the cavitating region. The energy equation used considers the effects of heat conduction and convection, viscous heating, and the heat of evaporation. The developed method has been applied to a series of cases of lubricated metal-on-metal line contact with an entrainment velocity of uent=2.5m∕s, viscosities η0=[0.01,1]Pas, and slide-to-roll ratios SRR=[0,1,2] under both thermal and isothermal conditions. The isothermal results are compared to the Reynolds theory and most results agree very well. Only the high-viscosity pure rolling case shows small differences. The combined effects of temperature, pressure, and shear-thinning are studied for the thermal cases. A temperature-induced shear band occurs in the case of sliding combined with very large viscosity compared to the isothermal case, which results in significant pressure variations across the thickness of the film. The impact of temperature on the friction force is discussed, showing differences of up to −88.5% compared to the isothermal case. The developed method is capable of giving new insights into the physics of elastohydrodynamic lubrication, especially in cases where the usual assumptions of the Reynolds theory break down.

Optical measurements of the hot spot and incandescent shock from high pressure cavitation in water

Spontaneous acoustic cavitation in water at static pressure up to 300 bar has been experimentally investigated. Cavities are initiated by negative pressure and then collapse due to both acoustic pressure and shock waves reflected from the inner surface of the spherical resonator. The implosions result in intense (Mbar) shock waves and bright (1 nJ) light flashes which last from 5 to 40 nanoseconds. The optical spectrum of the flash is measured with a grating monochromator and intensified array detector for high wavelength resolution (̃5 nm) but slow time resolution, and with a multiple-anode microchannel plate photomultiplier tube along with bandpass filters for fast time resolution (̃1 ns) but poor wavelength resolution. The spectrum is generally broad-band and featureless, matching roughly to a Planck spectrum at 5000 to 8000K. The spectral and temporal structure of the flashes is matched to hydrocode simulations. The model suggest the flashes are due to a shell of hot, opaque, shocked water which surrounds and obscures the central hot core. (SMDC contract W9113M-07-C-0178)

Surface Roughness and Pressure Effect on Viscosity in Elastohydrodynamic Lubrication Model of Engine Bearings (Friction)

In this study, Patir and Cheng's surface roughness model is introduced in a mass conserving elastohydrodynamic lubrication model of a dynamically loaded journal bearing and described consistent with the model of regular striations. The lubrication model is based on a modified Elrod's cavitation algorithm and pressure effect on viscosity is expressed by Barus's equation. The model was applied to a con-rod big-end bearing of an engine and the effect of surface texture, roughness and striations, on friction power loss was calculated. The friction power loss of the bearing with circumferential striations is the lowest and is as much as that of the bearing with a smooth surface. The friction power loss of the bearing with transversal striations is the highest. The friction power losses of the bearing with the surface roughness take the value between them according to directional ratio. The results also showed the pressure effect on viscosity plays an important role in the friction power loss.