Technology & Engineering
Cavitation
Cavitation is the formation and collapse of vapor bubbles in a liquid due to rapid changes in pressure. In engineering, it can occur in pumps, propellers, and other fluid systems, leading to erosion and damage. Understanding and managing cavitation is important for designing efficient and durable fluid-handling equipment.
Written by Perlego with AI-assistance
Related key terms
1 of 5
11 Key excerpts on "Cavitation"
eBook - ePub- John Carlton(Author)
- 2018(Publication Date)
- Butterworth-Heinemann(Publisher)
Chapter 9Cavitation
Abstract
Cavitation is a general fluid mechanics phenomenon that can occur whenever a liquid is used in a machine, which induces pressure and velocity fluctuations in the fluid. Consequently, pumps, turbines, propellers, bearings, and even the human body, for example, the heart and knee joints, are all examples of machines where the destructive consequences of Cavitation may occur. While Cavitation sometimes has undesirable consequences, this however need not always be the case in situations such as drug delivery, the cutting of rocks or steel plates.Keywords
Cavitation; Propeller; Vapor pressure; Velocity; Fluid; Cavitation inceptionChapter Outline-
9.1 The Basic Physics of Cavitation
-
9.2 Types of Cavitation Experienced by Propellers
-
9.2.1 Sheet Cavitation
-
9.2.2 Bubble Cavitation
-
9.2.3 Cloud Cavitation
-
9.2.4 Propeller Vortex Cavitation Types
-
9.2.5 Propulsor-Hull Vortex Cavitation
-
9.2.6 Full Scale Observations of Cavitation
-
9.2.1
-
9.3 Cavitation Considerations in Design
-
9.4 Cavitation Inception
-
9.5 Cavitation-Induced Damage
-
9.6 Cavitation Testing of Propellers
-
9.7 Analysis of Measured Pressure Data From a Cavitating Propeller
-
9.8 The Prediction of Cavitation
-
Bibliography
Cavitation is a general fluid mechanics phenomenon that can occur whenever a liquid is used in a machine, which induces pressure and velocity fluctuations in the fluid. Consequently, pumps, turbines, propellers, bearings, and even the human body, for example, the heart and knee joints, are all examples of machines where the destructive consequences of Cavitation may occur. While Cavitation sometimes has undesirable consequences, this however need not always be the case in situations such as drug delivery, the cutting of rocks or steel plates.The history of Cavitation has been traced back to the middle of the 18th century, when some attention was paid to the subject by the Swiss mathematician Euler (1756)
eBook - PDFTurbomachinery
Design and Theory
- Rama S.R. Gorla, Aijaz A. Khan(Authors)
- 2003(Publication Date)
- CRC Press(Publisher)
8 Cavitation in Hydraulic Machinery 8.1 INTRODUCTION Cavitation is caused by local vaporization of the fluid, when the local static pressure of a liquid falls below the vapor pressure of the liquid. Small bubbles or cavities filled with vapor are formed, which suddenly collapse on moving forward with the flow into regions of high pressure. These bubbles collapse with tremendous force, giving rise to as high a pressure as 3500 atm. In a centrifugal pump, these low-pressure zones are generally at the impeller inlet, where the fluid is locally accelerated over the vane surfaces. In turbines, Cavitation is most likely to occur at the downstream outlet end of a blade on the low- pressure leading face. When Cavitation occurs, it causes the following undesirable effects: 1. Local pitting of the impeller and erosion of the metal surface. 2. Serious damage can occur from prolonged Cavitation erosion. 3. Vibration of machine; noise is also generated in the form of sharp cracking sounds when Cavitation takes place. 4. A drop in efficiency due to vapor formation, which reduces the effective flow areas. The avoidance of Cavitation in conventionally designed machines can be regarded as one of the essential tasks of both pump and turbine designers. This Cavitation imposes limitations on the rate of discharge and speed of rotation of the pump. 8.2 STAGES AND TYPES OF Cavitation The term incipient stage describes Cavitation that is just barely detectable. The discernible bubbles of incipient Cavitation are small, and the zone over which Cavitation occurs is limited. With changes in conditions (pressure, velocity, temperature) toward promoting increased vaporization rates, Cavitation grows; the succeeding stages are distinguished from the incipient stage by the term developed. Traveling Cavitation is a type composed of individual transient cavities or bubbles, which form in the liquid, as they expand, shrink, and then collapse.
eBook - ePubCavitation
Bubble Trackers
- Yves Lecoffre(Author)
- 2021(Publication Date)
- Routledge(Publisher)
11Cavitation Erosion
11.1 INTRODUCTION
As indicated earlier, pressure reductions in high velocity flows can be so large that vaporisation may occur locally; this is the phenomenon termed ‘Cavitation’. Vaporous bubbles formed in the process are carried by the flow downstream of the cavitating zone. They condense suddenly; the higher the pressure gradients encountered, the more rapid the condensation.Fig. 11.1. Hydrodynamic mechanism of erosion by Cavitation.If this sudden condensation, often called ‘collapse’, occurs near a solid body, the velocity of the bubble walls at the end of the process can become sufficiently high to cause a local and steady attack of the material[295 ]. The combined effect of these impacts leads sooner or later to failure and tearing of the material; this is Cavitation erosion. Photo no. 15 is an example of the damage suffered by the rotor of a pump.11.2 RELEVANT COMPONENTS
Cavitation occurs in all standard hydraulic components, pumps, valves, turbines and propellers. As we have seen, when Cavitation develops under the influence of an increase in velocity, it is accompanied by the following effects:Photo no. 15. Cavitation erosion on the rotor of a pump.- — Noise. This is the first manifestation of the phenomenon. It is characterised either by a crackling sound in large machines or a whistling sound in regulating valves. The appearance of noise is regarded as a limit in the applications of naval propulsion. As soon as a liquid flow starts emitting noise it should be suspected that Cavitation has occurred:
- — Vibrations. When Cavitation develops, noise is replaced by vibrations. They are particularly troublesome in high power machines.
- — Erosion. When Cavitation is sufficiently extended and flow velocities large, erosion occurs on the walls of the components, often rapidly;
- — Loss of performance. Finally, in a highly developed state Cavitation leads to a loss of output of machines. This criterion is regarded as a limit for approval in the case of standard small hydraulic machines. In particular, the NPSH of commercial pumps corresponds to a loss of 3% in the output.
eBook - PDFAdvances in Hydroscience
Volume 12
- Ven Te Chow(Author)
- 2013(Publication Date)
- Academic Press(Publisher)
If the local pressure is lowered further, more profuse Cavitation occurs. Sometimes large vapor-filled cavities develop that remain attached to solid surfaces. When these cavities form on lifting surfaces, such as hydrofoils or the blades of pumps or turbines, there is a marked change in the flow field, resulting in performance degradation. Small bubbles are still formed on the surface of these cavities, and they are swept into the wake of the large cavity where collapse occurs. Again the result is the same: noise, vibration, and damage if the collapse is adjacent to a solid boundary. It should be mentioned at this point that although Cavitation is normally considered an undesirable effect or phenomenon, it sometimes serves useful purposes. A case in point is found in the ultrasonic cleaning of various surfaces, where intense sound waves are used to produce Cavitation, which in turn performs a cleaning function. For example, milk is homogenized using Cavitation. Various types of chemical processes are enhanced by Cavitation, such as coagulation and formation of suspensions. We use Cavitation for degassing liquids. Sometimes we can use Cavitation to increase heat and mass transfer in liquids, to promote crystallization, and to enhance various sonochemical reactions such as polymerization and polymer degradation. An enormous quantity of literature has been generated on the subject of Cavitation and several very extensive reviews are already available, e.g., the review by Eisenberg (10) and the book by Knapp et al. (77). It is not the intent of this review to cover the entire subject of Cavitation. An attempt is made to introduce the reader to the breadth of the subject, to illustrate the various aspects of Cavitation, and then finally to concentrate on recent research in the area of Cavitation inception, followed by a more cursory look at work going on in the areas of Cavitation erosion and Cavitation noise.
eBook - ePub- Richard M. Pashley, Marilyn E. Karaman(Authors)
- 2021(Publication Date)
- Wiley(Publisher)
In industry, the effects of Cavitation in fluid systems, Cavitation wear, fluid oxidation/degradation and fouling in aqueous systems are dealt with via design compromises and the development of new materials, coatings, various fluid additives and regular maintenance. It is well known that Cavitation phenomena have an effect on the efficiency of fluid transmission and lead to material degradation in hydraulic systems. All fluid pumping installations are designed to prevent Cavitation in order to ensure steady fluid flow through piping. Furthermore, the maximum shaft speed of centrifugal pumps and therefore the fluid velocity, flow rate and head obtainable from them are limited by the need to ensure that Cavitation does not occur at the leading edge of the pump impeller(s). Otherwise, unsteady and variable mass flow, noise, vibration and, in some instances, ‘choking’ or flow collapse results once sufficient air bubbles form at the impeller hub under the action of centrifugal forces.In fluid Cavitation, it is generally assumed that local suction pressures just below the vapour pressure of a fluid, at a given temperature, will nucleate bubbles which then implode once local hydrostatic pressure returns. In practice, there is a significant additional barrier to the formation of cavities in the absence of suitable nucleation sites, and it is actually very difficult to cavitate pure liquids in clean, smooth vessels. Nano‐sized cavities are usually the smallest structures which can be considered as a separate phase, and their growth or collapse controls the extent of Cavitation. The presence of dissolved atmospheric gases facilitates fluid Cavitation. For example, water can dissolve close to 20 mL of atmospheric gases per litre, and oils typically ten times more. The removal of these dissolved gases inhibits fluid Cavitation. The prevention of fluid Cavitation by degassing can improve a wide range of processes, such as pumping efficiency, reduce corrosion and wear in fluid systems, prevent oxidation and degradation of liquids and assist in the prevention of inorganic fouling related to corrosion. Degassing will also reduce bio‐fouling and related microbial growth in liquids and gels.
eBook - PDF- E.C. Fitch(Author)
- 2013(Publication Date)
- Elsevier Science(Publisher)
• Observation of surface discontinuities that can cause very high cavitating flow fields particu-larly if they occur on the low-pressure side of the flow passage and if the discontinuity turns away from the flow. The above discussion should show that no section within a fluid system subjected to flow-ing conditions is exempt from the possibility of Cavitation. All lines, filters, heat exchang-ers, line intrusive transducer, and fittings are susceptible. Even sealing interfaces are candi-date Cavitation areas—particularly rotary face seals. The Cavitation subject deserves con-siderable more research effort now that proper attention has been focused on its performance degradation and material destruction power. 6.9 Cavitation DAMAGE Cavitation is the dynamic process of cav-ity growth and collapse in a moving fluid. Cavitation damage of adjacent material takes place when fatigue action from microjets form from the implosion of vapor bubbles. These Cavitation jets form and produce such rapid effects that the fluid behaves like a solid, with pressures great enough to damage any mate-rial. Cavitation damage depends on many fac-tors. For a given material and fluid velocity, the following fluid characteristics are extremely important—vapor pressure, air content, surface tension, and fluid viscosity. The amount of material that the Cavitation process removes is proportional to the load imposed on the surface. The impact jet generates this load as bubbles collapse on the material's surface. The velocity of the Cavitation jet force is 2 to 8 times the bubble contraction velocity. The velocity required to create the necessary impact force is a function of the bubble size and bubble contraction velocity. The bubble size is a function of how close the system pressure is to the vapor pressure of the fluid. Low inlet pressures generate pressures close to vapor in the pump suction chamber as the graph in Fig.
eBook - PDF- P. Germain, M. Piau, D. Caillerie(Authors)
- 2012(Publication Date)
- North Holland(Publisher)
Theoretical and Applied Mechanics P. Germain, M. Piau and D. Caillerie (Editors) Elsevier Science Publishers B.V. (North-Holland) 369 © IUTAM, 1989 SOME PHYSICAL PHENOMENA ASSOCIATED WITH Cavitation J.H.J. VAN DER MEULEN Maritime Research Institute Netherlands Wageningen, The Netherlands The collapse of Cavitation bubbles near a boundary may be accompanied by jet or counterjet formation, the generation of a vortex cavity of toroidal shape, rebound shock waves and other physical phenomena. The important parameter appears to be the proximity of the bubble to the boundary. Physical effects associated with bubble collapse in acoustic or hydrodynamic Cavitation are luminescence, noise and erosion. It is shown that all of these effects can be used as measures of Cavitation intensity for hydrodynamic Cavitation. 1. INTRODUCTION Acoustic and hydrodynamic Cavitation are related to sound fields or low pressure regions in a flow field. In general, Cavitation can be regarded as a process in which different phases can be discerned. These phases are: inception, growth, motion and collapse. In recent years a considerable amount of both theoretical and experimental work has been done to predict and describe the implosion behaviour of single Cavitation bubbles, or clusters of cavities, near a boundary. In section 2 of the present paper new developments in this field are reviewed. The collapse of bubbles may produce physical effects, such as noise, erosion and luminescence. In the field of acoustic Cavitation, luminescence has been studied in great detail. Some work on the origin of this phenomenon is discussed in section 3 of this paper. In section A, it is shown that hydrodynamic Cavitation may also produce luminescence. The assessment of the intensity of hydrodynamic Cavitation can thus be based on measuring the intensity of noise, erosion or luminescence. Some new developments in this field are presented. 2.
eBook - PDF- Shengcai Li(Author)
- 2000(Publication Date)
- ICP(Publisher)
Nevertheless, the detailed information about the magnitude of pressures and the process of surface fracture caused by these impulses are still not available. It is still an ongoing research sub-ject. Cavitation in hydraulic machinery often appears in the cloud form 269 270 Cavitation I I f i Investigator Rayleigh Hickling and Plesset Ivany and Hammitt Plesset and Chapman Jones and Edwards Fujikawa and Akamatsu Tomita and Shima Bubbles Empty bubble Gas bubble Initial gas pressure: Pg=10 3 atm Gas bubble Initial gas pressure: Pg=10 3 atm Pg-10 * atm Vapour bubble Spark-induced hemisherical bubble H2 gas in a water shock tube Spark-induced bubble Methods for calculation or measurement of collapse pressure Spherical incompressible Spherical compressible Spherical compressible Based on micro jet velocity Piezoelectric pressure-bar guage Pressure guage Holographic interferometry Pressure transducer Photoelasticity Results 1260 atm at the stage of 1/20 of initial radius 4 <2 X 10 atm 6.77 X 10 4 atm 5.82 X 10 5 atm 2X 1 0 3 atm 10 4 atm Time duration: 2-3 us 10 4 -10 5 atm Several 10 MPa Ref. [1] [2] [3] [4] [5] [6] [7] Table 6.1: Bubble collapse pressures Cavitation Damage to Hydraulic Machinery 271 consisting of many Cavitation bubbles. When such a cloud collapses on or near the face of a boundary, the surface is exposed to such bubble-collapse pressures that possess different magnitudes. This is because the bubble size, shape and the collapsing location etc are all different. Each of these im-pulses acts in a localised tiny area and over a very short duration. The pressure acting area and the duration are important factors which affect the mechanism of Cavitation damage. Nowadays, some measuring techniques enable us to estimate these collapse pressures to a certain accuracy.
- Yufeng Zhou(Author)
- 2015(Publication Date)
- CRC Press(Publisher)
Brennen CE. Cavitation in biological and bioengineering contexts. 5th International Symposium on Cavitation , Osaka, Japan, 2003, pp. 1–9. Brenner MP, Hilgenfeldt S, Lohse D. Single-bubble sonolumines-cence . Reviews of Modern Physics 2002;74:425–484. Brett HWW, Jellinek HHG. Degradation of long chain molecules by ultrasonic waves. Part V. Cavitation and the effect of dissolved gases . Journal of Polymer Science Part A 1954;13:441–459. Briggs LJ. Limiting negative pressure of water . Journal of Applied Physics 1950;21:721–722. Brotchie A, Statham T, Zhou M, Dharmarathne L, Grieser F, Ashokkumar M. Acoustic bubble sizes, coalescence, and sonochemical activity in aqueous electrolyte solutions satu-rated with different gases . Langmuir 2010;26:12690–12695. Brujan E-A, Nahen K, Schmidt P, Vogel A. Dynamics of laser-induced Cavitation bubbles near an elastic boundary . Journal of Fluid Mechanics 2001;433:251–281. Caupin F, Herbert E. Cavitation in water: A review . Comptes Rendus Physique 2006;7:1000–1017. Ceccio SL, Brennen CE. Observations of the dynamics and acoustics of travelling bubble Cavitation . Journal of Fluid Mechanics 1991;233:633–660. Chen H, Kreider W, Brayman AA, Bailey MR, Matula TJ. Blood vessel deformations on microsecond time scales by ultrasonic Cavitation . Physical Review Letters 2011;106:034301. Chen W-S, Matula TJ, Brayman AA, Crum LA. A comparison of the fragmentation thresholds and inertial Cavitation doses of different ultrasound contrast agents . Journal of the Acoustical Society of America 2003;113:643–651. Chin CT, Lancée C, Borsboom J, Mastik F, Frijlink ME, de Jong N, Versluis M, Lohse D. Brandaris 128: A digital 25 million frames per second camera with 128 highly sensitive frames . Review of Scientific Instruments 2003;74:5026–5034. Church CC. A theoretical study of Cavitation generated by an extra-corporeal shock wave lithotripter . Journal of the Acoustical Society of America 1989;86:215–227.
eBook - PDF- Christopher Earls Brennen(Author)
- 2013(Publication Date)
- Cambridge University Press(Publisher)
(1955). On the mechanism of Cavitation damage. Trans. ASME, 1055–1064. Plesset, M.S. and Mitchell, T.P. (1956). On the stability of the spherical shape of a vapor cavity in a liquid. Quart. Appl. Math., 13, No. 4, 419–430. Plesset, M.S. and Chapman, R.B. (1971). Collapse of an initially spherical vapor cavity in the neighborhood of a solid boundary. J. Fluid Mech., 47, 283–290. 88 Cavitation Bubble Collapse Plesset, M.S. and Prosperetti, A. (1977). Bubble dynamics and Cavitation. Ann. Rev. Fluid Mech., 9, 145–185. Prosperetti, A. and Lezzi, A. (1986). Bubble dynamics in a compressible liquid. Part 1. First- order theory. J. Fluid Mech., 168, 457–478. Rayleigh, Lord (Strutt, John William). (1917). On the pressure developed in a liquid during the collapse of a spherical cavity. Phil. Mag., 34, 94–98. Schneider, A.J.R. (1949). Some compressibility effects in Cavitation bubble dynamics. Ph.D. Thesis, Calif. Inst. of Tech. Shima, A., Takayama, K., Tomita, Y., and Miura, N. (1981). An experimental study on effects of a solid wall on the motion of bubbles and shock waves in bubble collapse. Acustica, 48, 293–301. Shima, A., Takayama, K., Tomita, Y., and Ohsawa, N. (1983). Mechanism of impact pressure generation from spark-generated bubble collapse near a wall. AIAA J., 21, 55–59. Soyama,H., Kato, H., and Oba, R. (1992). Cavitation observations of severely erosive vortex Cavitation arising in a centrifugal pump. Proc. Third I. Mech. E. Int. Conf. on Cavitation, 103–110. Taylor, K.J. and Jarman, P.D. (1970). The spectra of sonoluminescence. Aust. J. Phys., 23, 319–334. Theofanous, T., Biasi, L., Isbin, H.S., and Fauske, H. (1969). A theoretical study on bubble growth in constant and time-dependent pressure fields. Chem. Eng. Sci., 24, 885–897. Thiruvengadam, A. (1967). The concept of erosion strength. In Erosion by Cavitation or impingement. Am. Soc. Testing Mats. STP 408, 22–35. Thiruvengadam, A.
eBook - ePub- John Carlton(Author)
- 2012(Publication Date)
- Butterworth-Heinemann(Publisher)
Notwithstanding the wavelet class of methods, the double integral approach has been shown to be the most successful at phenomenological discrimination. The pressure integration approach is essentially a time domain process, which together with visual observations of Cavitation can link the dynamics of visual events with the dynamics of pressure pulses. It is clear from both ship and model-scale analysis of such data that the more severe excitation events are generated by Cavitation which grows, collapses and rebounds in a small cylindrical sector of the propeller disc and slipstream which spans the wake peak. It is the passage of the propeller blades through this slow-speed region which causes the flare-up and collapse of cavity volumes on the blade and in the tip vortex shed by the advancing blade.9.8 The CFD Prediction of Cavitation
With the growth in computer-based capabilities, considerable effort is being expended in the development of methods to predict the extent and characteristics of the Cavitation development over propeller blades.Many of the computational fluid dynamics models that are used for Cavitation studies use a barotropic equation of state using the relationship ρ = ρ(p) which assumes that the mixture density is a function of the local pressure. This implies that all of the effects caused by bubble content are disregarded except for the compressibility and that the bubbly mixture can be regarded as a single-phase compressible fluid. Normally the methods employing a barotropic state law assume a continuous variation of density between liquid and vapor values in a range of pressures centered on the vapor pressure. Such approaches are attractive because of their simplicity but it has to be recognized that they assume equilibrium thermodynamics in their solution.In practice, the transient dynamics of Cavitation are important. Cavitation inception is associated with the growth of nuclei with diameters in the range 10−5 to 10−3
Index pages curate the most relevant extracts from our library of academic textbooks. They’ve been created using an in-house natural language model (NLM), each adding context and meaning to key research topics.
