Search results for "Cavitation"

Contribution to the study of spray formation

2012

The work of this thesis aims to provide and validate tools useful to study and understand the phenomena involved in the injection of fuel, mainly focused on intra-flow injector. These tools are numeric and simulate the formation of a spray. A first part focuses on zero-dimensional modelling. Models which predict these following characteristics of spray like the spray angle, the spray penetration or the liquid length are compared with experimental data. The conclusions are that zero-dimensional modelling provides good results very quickly in some cases. Although, a better understanding of the influence of cavitation on the spray, which requires an understanding of the intra-flow injector, co…

Thermal nucleation of cavities in liquid helium at negative pressures

1993

We have investigated the nucleation rate at which cavities are formed in $^{4}\mathrm{He}$ and $^{3}\mathrm{He}$ at negative pressures due to thermal fluctuations. To this end, we have used a density functional that reproduces the He liquid-gas interface along the coexistence line. The inclusion of thermal effects in the calculation of the barrier against nucleation results in a sizable decrease of the absolute value of the tensile strength above 1.5 K.

Magnetically Induced Cavitation for the Dispersion of Particles in Liquid Metals

2018

A contactless excitation of cavitation is possible by superposition of induction heating with a static axial magnetic field. This creates an alternating electromagnetic body force in a liquid metal which in turn produces pressure oscillations. Using this method, the onset of cavitation has been clearly observed in various liquid metals (tin, zinc, aluminum, steel SAE 304) at pressure oscillations in the range of 28…50 kPa. The present study aims to extend the previous work by producing steel metal matrix composites (MMC) and assessing the feasibility of the proposed method for particle dispersion in steel. Stainless steel (SAE 316L) samples with different ceramic inclusions, e.g. TiN, Al2O3…

A Numerical Approach to Finite Journal Bearings Lubricated With Ferrofluid

1987

Several cases of cylindrical bearings lubricated with ferrofluid are examined by means of a finite-difference numerical procedure. The subregion of cavitation is determined by imposing mass conservation across the “rupture” and “reformation” boundaries of the complete film. The examined cases refer to bearings confined by sealing rings formed by the lubricant itself, for which there is no need of external supply. In each case the most significant parameters are calculated and it is possible to see that the use of these bearings is favorable when speeds are low, clearances large, and loads light, because in such conditions the magnetic effects are comparable with the pure hydrodynamic ones a…

High-speed rotational angioplasty-induced echo contrast in vivo and in vitro optical analysis

1992

High-speed rotational angioplasty is being evaluated as an alternative interventional device for the endovascular treatment of chronic coronary occlusions. It has been postulated that this type of angioplasty device may produce particulate debris or cavitations that induce myocardial ischemia. To determine the clinical presence of myocardial ischemia during rotational angioplasty, echocardiographic monitoring for wall motion abnormalities was performed in 9 patients undergoing rotational atheroablation using the Auth Rotablator for 10-sec intervals at 150,000 and 170,000 rpm. No wall motion abnormalities were detected in 5 patients evaluated with transesophageal echocardiography or in 4 pat…

2019

Abstract The fatigue life of thermally sprayed Al2O3- and Cr2O3-based coatings has been studied under low-energy (0.7–5 mJ) impact conditions. A threshold impact energy and amount of repetitions the coatings can endure with said energy before catastrophic failure was obtained. The catastrophic failure was determined to occur when the fracture mode of the coating switched from brittle cone cracking to quasi-plastic radial cracking. The results are examined relative to the microstructural features along with other properties of the coatings - hardness and cavitation resistance. The experiment provided a new approach for a straightforward comparison of the micro-scale impact fatigue life of th…

Influence of pressure on ultrasonic cavitation activity in room temperature ionic liquids: An electrochemical study

2019

Abstract This paper provides proofs of the respective contributions of dissolved gases and solvent vapor on cavitation activity in sonoreactors. This activity can be detected by electrochemistry because the fluctuating events measured at the electrode surface are only linked to physical effects of cavitation. As ionic liquids present very low volatilities, their vaporization is reduced, and cavitation bubbles only depend on the presence of gases. Then, cavitation activity may be trigged by reactor atmosphere control. Applying severe depression within an irradiated ionic liquid medium contributes to removing dissolved gases, thus quenching cavitation activity. A specific sonoelectrochemical …

The use of non-cavitating coupling fluids for intensifying sonoelectrochemical processes

2020

Abstract For the first time, we have investigated the beneficial effects of non-cavitating coupling fluids and their moderate overpressures in enhancing mass-transfer and acoustic energy transfer in a double cell micro-sonoreactor. Silicon and engine oils of different viscosities were used as non-cavitating coupling fluids. A formulated monoethylene glycol (FMG), which is a regular cooling fluid, was also used as reference. It was found that silicon oil yielded a maximum acoustic energy transfer (3.05 W/cm2) from the double jacketed cell to the inner cell volume, at 1 bar of coupling fluid overpressure which was 2.5 times higher than the regular FMG cooling fluid. It was also found that the…

A micro-mechanical model for grain-boundary cavitation in polycrystalline materials

2015

In this work, the grain-boundary cavitation in polycrystalline aggregates is investigated by means of a grain-scale model. Polycrystalline aggregates are generated using Voronoi tessellations, which have been extensively shown to retain the statistical features of real microstructures. Nucleation, thickening and sliding of cavities at grain boundaries are represented by specific cohesive laws embodying the damage parameters, whose time evolution equations are coupled to the mechanical model. The formulation is presented within the framework of a grain-boundary formulation, which only requires the discretization of the grain surfaces. Some numerical tests are presented to demonstrate the fea…

Ultrasound-assisted bleaching: Mathematical and 3D computational fluid dynamics simulation of ultrasound parameters on microbubble formation and cavi…

2019

Abstract The implementation of ultrasound-assisted bleaching (UAB) is gaining interest in commercial oil refining, as an alternative to the current bleaching procedure (BP), because this technique has several advantages compared to the conventional BP. The mathematical and 3D computational fluid dynamics (CFD) simulation of the influence of ultrasound power, frequency and temperature for predicting microbubble formation and heat transfer in the ultrasonic treatment of soybean oil was assessed in order to optimize the UAB process. The fluctuation frequency and wave speed showed opposite effects on system response to the imposed pressure pulse. As the bubble radius shrinks to zero (after bubb…