Hydrodynamic cavitation dynamics

It can be said that acoustic and hydrodynamic cavitation are the result of the tensions prevailing in a liquid, while optic and particle cavitation are the consequence of the local deposition of energy. The classification scheme for the phenomena of cavitation has been shown schematically in Fig. 2.1. Once the cavities are generated, subsequent expansion of the minute cavity may be achieved by reducing the ambient pressure using static or dynamic means. The surrounding... 

Kanthale PM, Gogate PR, Wilhelm AM, Pandit AB (2005) Dynamics of cavitational bubbles and design of a hydrodynamic cavitational reactor cluster approach. Ultrason Sonochem 12 441 -52... 

Analysis on the Basis of Bubble Dynamics The bubble behavior and hence the pressure pulse generated at the collapse of the cavity in the case of hydrodynamic cavitation depends upon the operating conditions as well as the geometry of the mechanical constriction that results in the generation of cavitating conditions downstream of the orifice. Thus, as a first step towards the design of hydrodynamic-cavitation reactors, it is important to understand the relationship between the cavity behavior and the operating parameters and possibly quantify the intensity of cavitation and then the net cavitational effects as a direct function... 

The effect of polymeric additives on collective phenomena, associated with the dynamics of bubbles, can be illustrated by the example of hydrodynamic cavitation, caused by abrupt decrease in local pressure (in flows around bodies, after stream contraction, in jets). It has been found that the use of polymers permits to decrease the cavitation noise, lower the cavitation erosion, and delay the cavitation inception. For example, adding a small amount of POE to a water jet issuing from the orifice caused the decrease of the critical cavitation number, K , by 35-40%. In experiments with rotating disk flic value of K, was decreased by 65% with addition of 500 ppm POE. Note, however, that these features are linked not only to the changes in individual bubble dynamics, but to the influence of macromolecules on the total flow regime as well. In particular, phenomena listed above are... 

A.P. Keller and E.A. Weitendorf, A determination of the free air content and velocity in front of the Sydney-Express propeller in connection with pressure fluctuation measurements, in Twelfth Symposium on Naval Hydrodynamics Boundary Layer Stability and Transition, Ship Boundary Layers and Propeller-Hull Interaction, Cavitation, and Geophysical Fluid Dynamics, National Academy of Sciences, Wash. DC, 1979, pp. 300-318. 

The bubble-dynamics equations are very similar to acoustic cavitation the only difference being the fact that the surrounding fluctuating pressure field is driven by hydrodynamic conditions existing downstream of the constriction, whereas in the case of acoustic cavitation, it is dependent on the frequency and intensity of the ultrasonic irradiation (sinusoidal variation). There are two approaches used for the estimation of the local pressure at any location downstream of the constriction (the typical pressure recovery profiles are shown in Fig. 8.2.6). 

This paper presents the results of a theoretical study of the oil film forces, arising from combined hydrodynamic squeeze and wedge actions, in a dynamically loaded bearing. In particular, it shows how the non-linearity of the force-journal velocity relationship is dependent upon cavitation. Simple equations for the total oil film force components, at any given eccentricity ratio, are fitted to the predicted force-velocity data. These equations introduce five velocity coefficients, which take account of the non-linear behaviour. Application of these equations to a fast journal orbit analysis, including comparison with experimental results, is described in reference (5). 

However, hydrodynamic similarity in both the steadily and dynamically loaded situations is also dependent upon the geometric similarity of the cavitation zone boundary relative to the bearing surface boundary. The cavitation zone boundary is dependent on the oil film boundary pressures P3 and P(,. In order to fulfil the above requirement for geometric similarity with respect to cavitation, the following dimensionless parameters must also be held constant ... 

Cavitation, the phenomenon that causes liquids to rupture and to form vaporous/gas cavities when subjected to sufficiently low pressures, can occur in any machine handling liquid when requisite hydrodynamic conditions develop (Fig. 1). Cavitation, in many cases, is an undesirable phenomenon in hydraulic machinery that can limit performance, lower efficiency, introduce sever structural vibration, generate acoustic noise, choke flow and cause catastrophic damage [1]. The pernicious effects of hydro-dynamic cavitation on conventional fluid machinery have been recognized and actively researched in the last century. Present knowledge (experimental and analytical) of cavitation has contributed immensely towards improving the design of conventional scale fluid machinery. 

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