Fluid dynamics of acoustic and hydrodynamic cavitation in hydraulic power systems

Abstract

Cavitation is the transition from a liquid to a vapour phase, due to a drop in pressure to the level of the vapour tension of the fluid. Two kinds of cavitation have been reviewed here: acoustic cavitation and hydrodynamic cavitation. As acoustic cavitation in engineering systems is related to the propagation of waves through a region subjected to liquid vaporization, the available expressions of the sound speed are discussed. One of the main effects of hydrodynamic cavitation in the nozzles and orifices of hydraulic power systems is a reduction in flow permeability. Different discharge coefficient formulae are analysed in this paper: the Reynolds number and the cavitation number result to be the key fluid dynamical parameters for liquid and cavitating flows, respectively. The latest advances in the characterization of different cavitation regimes in a nozzle, as the cavitation number reduces, are presented. The physical cause of choked flows is explained, and an analogy between cavitation and supersonic aerodynamic flows is proposed. The main approaches to cavitation modelling in hydraulic power systems are also reviewed: these are divided into homogeneous-mixture and twophase models. The homogeneous-mixture models are further subdivided into barotropic and baroclinic models. The advantages and disadvantages of an implementation of the complete Rayleigh-Plesset equation are examined.

Treatment of Solvent-Contaminated Water Using Vortex-Based Cavitation: Influence of Operating Pressure Drop, Temperature, Aeration, and Reactor Scale

“…Collapsing cavities generate very high localised temperature and pressure which in turn generates strongly oxidative hydroxyl radicals (7). Cavitation can be realised either ultrasonically or hydro-dynamically (7)(8)(9). Ultrasonic cavitation is energy intensive and is difficult to scale up (10).…”

Prospects of Using Hydrodynamic Cavitation for Enhancement of Efficiency of Fluid Working Medium Preparation Technologies

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“…For proper selection of hardware, technology, preparation of emulsions and other liquids there is a need for a common criterion for evaluation of effectiveness of such plants [14,21]. Let's make the analysis of specific features of processing and distribution of energy in rotating hydrodynamic units (RGDU) of various designs.…”

“…Analyzing cavitation plants and methods of energy transfer to working fluids, when activating processed medium two process schemes of the devices can be identified: as passive, when energy is transmitted to the flow upstream before entering the plant, and active, creating a flow in the plant [14,21].…”

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