Hydrodynamic cavitation through a bio-inspired fast-closing plunger mechanism: experiments and simulations.

Experimental and numerical results are reported for the internal and external flow fields evolving in a bio-inspired snapping plunger. The experimental evidence underlines the nature of the dynamic-coupling between the processes taking place inside and outside the device. Two main structures dictate the properties of the external flow field: a strong jet which is followed by a vortex ring. Internally, complex patterns of cavitating structures are simultaneously produced in the chamber and the venturi-like conduit. We find the cavitation cycle to be suitably described by the Rayleigh-Plesset model and, thus, proceed to characterize the coupling of both fields in terms of the fluctuations of the velocity. All main parameters, as well as the energy released to the fluid during the collapse, are found to be within the same order-of-magnitude of previously known experimental results for isolated bubbles of comparable size.

Bioinspired snapping-claw apparatus to study hydrodynamic cavitation effects on the corrosion of metallic samples.

A creative low-cost and compact mechanical device that mimics the rapid closure of the pistol shrimp claw was used to conduct electrochemical experiments, in order to study the effects of hydrodynamic cavitation on the corrosion of aluminum and steel samples. Current-time curves show significant changes associated with local variations in dissolved O2 concentration, cavitation-induced erosion, and changes in the nature of the surface corrosion products.

Note: design of a novel rotating magnetic field device.

A novel device to produce a rotating magnetic field was designed, constructed, and tested. The system consists of a Helmholtz coil pair which is mechanically coupled to a dc electric motor whose angular velocity is controlled. The coil pair generates a uniform magnetic field; the whole system is rotated maintaining the coils energized using brushes. The magnetic field strength is uniform (≈5.8 mT) for a workspace of about 100 mm along the rotation axis. The system remains free of undesirable high amplitude mechanical vibrations for rotation frequencies below 10 Hz. We verified the performance of the apparatus by conducting experiments with magnetic swimmers.

Spectroscopic and thermodynamic features of conical bubble luminescence.

The influence on luminescence from conical bubble collapse (CBL) with varying Ar gas content while perturbing the liquid 1,2-Propanediol (PD) has been investigated. The temporal, spatial, and spectral features were analysed with regards to the dynamics of collapse and liquid degradation. Sulphuric acid and sodium chloride were added to disturb the liquid. The following three cases were studied: PD/Ar, (I), (PD + H(2)SO(4))/Ar, (II), and (PD + H(2)SO(4) + NaCl)/Ar, (III). The intensities of those cases decrease as III > II > I. Temporally, single and multiple light emissions were found to occur. The pulse shape exhibited a large variety of profiles with a main maximum and up to two local maxima around the main maximum. These local maxima resembled those generated by laser cavitation. Spatially, no radial symmetry was detected in the light emissions. Spectrally, the Swan, CH and CN lines were observed at low volumes of gas and driving pressure. The ·OH radical and OH-Ar bands, as well as the Na and K lines, consistently appeared superimposed on an underlying continuum that almost disappeared in (III). The Na line was observed with two satellite diffuse bands representing Na-Ar complexes in (I) and (II), whereas in (III), only the line of sodium could be seen. Weak and diffuse emission lines from the Ar atom in the near-IR region were observed in (I) and (II). The proposed mechanism of bright CBL was based on the energy transfer from electron-excited homolytic cleavage products to the chromophore molecules generated during the collapse-rebound time line (~8200 K and ~1 ms of collapse time from model), which had accumulated inside the liquid and remained on the walls of cavity during the repetition of the collapse. A general mechanism for the bright CBL is broached.

Influence of liquid density on the parametric shape instability of sonoluminescence bubbles in water and sulfuric acid.

Parametric shape instability of sonoluminescing argon bubbles in water and aqueous H(2)SO(4) was numerically analyzed considering gas and liquid density variations. The employed model couples Gilmore, Tait (liquid) and van der Waals (gas) equations to simulate radial dynamics and density changes, respectively. Shape stability-instability zones in the P(a)-R(0) space resulted from a linear stability analysis. For the argon-water and argon-water-acid systems, numerical results indicate a rapid rise in both gas and liquid densities during final stages of bubble implosion which result in a stabilizing effect on the parametric instability.