Aglomeración acústica de partículas

PACS: 43.35, 43.25.-- Publicado en el Vol. XXXI, núm. 3-4, tercer y cuarto trimestre 2000 de la Revista de Acústica: Número especial dedicado al XXV Aniversario del Instituto de Acústica del C.S.I.C.[ES] En este trabajo se presenta una recopilación de las principales aportaciones llevadas a cabo en el campo de la aglomeración acústica de partículas desde 1972. A lo largo de este periodo de tiempo se ha consolidado esta línea de investigación. Se han estudiado y simulado numéricamente los mecanismos básicos del proceso de aglomeración. Paralelamente se han desarrollado y validado nuevos sistemas macrosónicos a escala de laboratorio y de planta piloto para la retención de partículas finas (0.1 - 2.5 μm) en efluentes industriales. Los principales logros científicos llevados a cabo en esta temática han dado lugar a más de setenta publicaciones internacionales.[EN] A summary of the most relevant R+D contributions since 1972 on the acoustic particle agglomeration is presented in this paper. Along this period the research topic has been well consolidated. The basic mechanisms involved in the agglomeration process have been studied and simulated numerically. In parallel, new macrosonic systems at laboratory and pilot plant scale have been developed and validated to reduce fine particle emissions (0.1 - 2.5 μm). The main scientific results obtained were published in more than seventy international papers.Peer reviewe

The Absorption of Sound in Suspensions Due to the Acoustic Wake Effect

Communication presented at the 17th International Congress on Acoustics, Rome, 2-7 September 2001.The absorption of sound in suspensions with particles much smaller than the acoustic wavelength is mainly due to the viscous drag between the fluid and the particles. In addition, viscous asymmetries generated in the flow field by the particles, partially entrained by the acoustic field, contribute to it. Such asymmetries, known as acoustic wakes, are considered in this work to derive the absorption coefficient based on the modification of the slip flow velocity. An experimental study is also presented where the value of the absorption coefficient is determined.Peer reviewe

Influence of the acoustic entrainment on aerosol particle interactions: experimental balance of the hydrodynamic mechanisms

6 pages, 5 figures.-- PACS nrs.: 43.25.Uv, 43.25.Nm.-- Communication presented at: Forum Acusticum Sevilla 2002 (Sevilla, Spain, 16-20 Sep 2002), comprising: 3rd European Congress on Acoustics; XXXIII Spanish Congress on Acoustics (TecniAcústica 2002); European and Japanese Symposium on Acoustics; 3rd Iberian Congress on Acoustics.-- Special issue of the journal Revista de Acústica, Vol. XXXIII, year 2002.A new experimental micro-scale study of particle interactions acoustically induced in monodisperse aerosols is presented in this work. It is devoted to the study of the influence exerted by the acoustic entrainment experienced by the single particles on their attraction processes and, in particular, on the hydrodynamic mechanisms that govern them. Glass spheres with certified diameters of 8.0 ± 0.9 μm immersed in air as dilute aerosols were subjected to homogeneous plane standing waves with a constant velocity amplitude U0 = 0.44 m/s at diverse frequencies, ranging from 200 Hz up to 5 kHz, at which the particles were much smaller than the respective acoustic wave-lengths.The experiments were carried out in the viscous forces domain with respect to the inertial forces, at a constant Reynolds number Re=0.24, in an emerging Oseen regime with very weak asymmetries in the flow field. For the first time this paper presents a complete collection of particle interactions at acoustic entrainments varying from qp=0.84 to qp =0.05, i.e., covering practically its complete range of variability.It is experimentally confirmed for the first time the presence of the mutual radiation pressure as a disturbing effect on the acoustic agglomeration generated on the aerosols, that is produced by the acoustic wake effect. Our results coincide with other previous researchs, agreeing with the theoretical prediction.Peer reviewe

Contribution of the Acoustic-Wake Effect to the Attenuation of Sound in Dilute Suspensions of Rigid Particles

5 páginas, 3 figuras, 1 tablaThis work deals with the attenuation of sound in dilute suspensions of rigid particles when the hydrodynamic mechanism of the acoustic-wake effect is considered. The study extends a previous model by considering asymmetric flow-field conditions around the particles, caused by other neighbor particles along the direction of propagation of the acoustic field. The attenuation coefficient is derived from the force equation for a spherical particle in an incompressible fluid that is oscillating at low frequencies and amplitudes within the range of Reynolds numbers of 0.1 < Re < 1. It acquires higher values than those obtained for the Stokes regime (Re << l), increasing up to ahout 8% at Reynolds numbers close to the unity. In the study we found the particle size as a significant parameter on the sound attenuation, together with concentration of particles.Peer reviewe

The influence of entrainment on acoustically induced interactions between aerosol particles—an experimental study

21 páginas, 15 figuras, 1 tablaAn experimental study of particle interactions acoustically induced in monodisperse aerosols is presented in this paper. It is mainly devoted to analyse the influence of the acoustic entrainment experienced by the single particles on their attraction processes and, in particular, on the hydrodynamic mechanisms that govern them. Glass micro-spheres immersed in air as very dilute aerosols were subjected to homogeneous plane standing waves at frequencies ranging from 200 Hz up to 5 kHz. At these variable acoustic conditions the particle experiences different acoustic entrainment coefficients, varying from qp=0:86 down to 0.05 and covering almost its complete range of variability. A collection of experimental particle interactions were filmed, from which the particle behaviours were analysed. Our results experimentally confirm for the first time the presence of the acoustic wake effect (AWE) as a dominant mechanism of attraction at every entrainment ratio. In addition, the mutual radiation pressure is observed as a repulsion mechanism acting on nearby particles (separated at few diameter distances). It produces a disturbing effect on the particle attractions due to the AWE. Its influence becomes negligible for entrainment coefficients below qp = 0:1.This work was supported by the Research Project CAM 07/M/0108/20009.Peer reviewe

Ultrasounds in cancer therapy: A summary of their use and unexplored potential

8 páginas, 2 tablasUltrasounds (US) are a non-ionizing mechanical wave, with less adverse effects than conventional pharmacological or surgical treatments. Different biological effects are induced in tissues and cells by ultrasound actuation depending on acoustic parameters, such as the wave intensity, frequency and treatment dose. This non-ionizing radiation has considerable applications in biomedicine including surgery, medical imaging, physical therapy and cancer therapy. Depending on the wave intensity, US are applied as high-intensity ultrasounds (HIUS) and low-intensity pulsed ultrasounds (LIPUS), with different effects on cells and tissues. HIUS produce thermal and mechanical effects, resulting in a large localized temperature increase, leading to tissue ablation and even tumor necrosis. This can be achieved by focusing low intensity waves emitted from different electrically shifted transducers, known as high-intensity focused ultrasounds (HIFU). LIPUS have been used extensively as a therapeutic, surgical and diagnostic tool, with diverse biological effects observed in tissues and cultured cells. US represent a non-invasive treatment strategy that can be applied to selected areas of the body, with limited adverse effects. In fact, tumor ablation using HIFU has been used as a curative treatment in patients with an early-stage pancreatic tumor and is an effective palliative treatment in patients with advanced stage disease. However, the biological effects, dose standardization, benefit-risk ratio and safety are not fully understood. Thus, it is an emerging field that requires further research in order to reach its full potential.The authors would like to acknowledge the following funding related with the effects of ultrasounds on cancer cells and tissues: Spanish National Plan project RETOS DPI 2017-90147-R. Intramural call for new research projects for clinical researchers and emerging research groups. IRYCIS. (2018/0240). Ibero-American Network CYTED-DITECROD-218RT0545

Precise measurements of particle entrainment in a standing-wave acoustic field between 20 and 3500 Hz

8 páginas, 6 figurasAn experimental study is presented to investigate entrainment coefficients of aerosol particles in a sonic wave. The experimental results are contrasted with a well-established analytical expressions for the entrainment coefficient derived from the Brandt-Freund-Hiedemann (BFH) equation. The measurements are carried out in a standing-wave field with an extremely homogeneous and well-determined acoustic velocity field. A CCD-camera with a microscope lens attachment is used to visualize the displacement amplitude of 7.9 km glass beads in the frequency range from 20 Hz to 3.5 kHz. The particle entrainment coefficients obtained with this visualization method are in good agreement with the theoretical predictions of the BFH equation and with earlier experimental data by Gucker and Doyle. While this prior study revealed some apparent experimental limitations, the present data is derived with an accurate and repeatable measurement technique. The large number of measurements in the current study helps to draw a detailed representation of the acoustic entrainment coefficient.This contract was supported by the research `Desarrollo y validacioó de nuevas tecnologías macrosónicas para la reducción de la emisión de partículas en efluentes gaseosos y líquidos de origen industrial" (proyecto CYCIT, AMB-96.1211-CO2-01) from the Spanish Ministery of Education and Science. The authors wish to acknowledge some valuable suggestions of Prof. S. Temkin.Peer reviewe

Visualization of Hydrodynamic Particle Interactions: Validation of a Numerical Model

8 páginas, 11 figurasAn experimental study is presented to investigate hydrodynamic interactions acoustically induced between particles in monodiperse aerosols. In particular, hydrodynamic mechanisms of viscous origin dominating these interactions are analyzed for several orientations of the particle center-lines with respect to the acoustic axis. The measurements were carried out in standing wave field with a homogeneous and well determined acoustic velocity field. A CCD-camera with a microscope lens attachment was used to visualize the displacements of 7.9 m glass beads in a frequency of 3 kHz under Oseen flow conditions. A number of 46 attraction processes between pairs of particles were visualized and quantified in the experiments. Maximal attractions were found for particles aligned along the acoustic field direction, requiring the shortest times to collide. These observations are in agreement with other previous experiments [1] carried out to verify the hydrodynamic interaction known as the “acoustic wake effect”. In the present paper the dependence of this interaction on the initial conditions of the particles is analyzed. Attractions become weaker when the angle formed by the particle center-line and the acoustic axis increases. Attraction patterns including collisions have been found and quantified for angles of the particle center-line up to 45Æ off the acoustic axis. The experimental data were positively compared with the results of a numerical study developed by the authors in a recent paper [2] in such a way that the numerical model has been now validated.This work was supported by the research projects CYCIT, TAP-93-0230 and CYCIT, AMB-96.1211-CO2-01) the Ministerio de Educaci´on y Ciencia of Spain. The authors would like thank D. Alfonso González and D. Enrique Costa for their valuable help in designing the optical setupPeer reviewe

Procedimiento y dispositivo ultrasónico para la eliminación de burbujas ocluidas en recubrimientos con pinturas y/o barnices aplicados a alta velocidad

Procedimiento y dispositivo ultrasónico para la eliminación de burbujas ocluidas en recubrimientos con pinturas y/o barnices aplicados a alta velocidad. Esta invención se refiere a un nuevo procedimiento ultrasónico y a un dispositivo para su implementación tecnológica destinado a eliminación de las burbujas ocluidas en las capas líquidas que constituyen los recubrimientos de superficies con pinturas y/o barnices. En estos procesos la formación de burbujas y microburbujas dentro de la capa líquida es relativamente frecuente. Tales burbujas, que se forman como consecuencia de la retención de aire, son difíciles de eliminar y particularmente en las aplicaciones a alta velocidad y en los procesos de secado rápido son causantes de imperfecciones e inhomogeneidades en el recubrimiento. El procedimiento objeto de la presente invención consiste en la aplicación de radiación ultrasónica de alta intensidad por vía aérea sobre la superficie de la capa líquida, inmediatamente después que esta haya sido depositada sobre el substrato y antes de que se produzca el secado del mismo.Peer reviewedConsejo Superior de Investigaciones Científicas (España)B1 Patente sin examen previ

Acoustophoretic particle manipulation in hybrid solid/gel resonators

10 páginas, 4 figuras, 1 tablaThis study presents a proof of concept to demonstrate the ability of ultrasounds to perform acoustophoretic processes in hybrid millifluidic resonators that include channels laterally embedded in extremely soft media with physical properties close to those of liquids. In our experiments, particles are driven by acoustic radiation forces toward hydrodynamic/acoustic equilibrium positions in a similar way to that produced in conventional microfluidic resonators with solid structures; 20 um-sized polystyrene beads immersed in deionized water flow channelized throughout an aqueous-based gel between an inlet and outlet in a resonant chamber while being exposed to ultrasounds at a frequency of 1.54 MHz. The liquid channel formed presents irregular walls and variable geometry defined by the sample injection pressure. Particles collect rapidly along a central line equidistant from the walls, regardless of whether they are parallel or not, as observed for different channel geometries and cross-sectional dimensions. Only when the flow stops, the particles collect in acoustic pressure nodes established with the 2D spatial distribution. These results break the paradigm of solid structures as essential physical elements to support acoustophoresis, demonstrating the ability to produce these processes in media without a consolidated structure. It opens a door to bioprinting applications.This research was supported and funded by the National Research Project DPI2017-90147-R of Spain and by the National Research Council of Spain CSIC through project i-COOPA20348. The trap device belonging to Bazou was used for the experiments