Enrique Riera

Separation method or supercritical fluid extraction assisted by high intensity ultrasound. Process for separation processes or supercritical fluid extraction assisted by high intensity ultrasound. The process of the present invention proposes the application of high intensity ultrasound to accelerate and improve the efficiency of the process of mass transfer in supercritical fluids, based on the separation process by contacting a substance containing extractable components with a solvent under supercritical or near to critical conditions. For the application of this procedure it has been developed based on the generation of a stationary ultrasonic field intense inside a vessel at standard pressure for supercritical fluids, and part of the present invention device. Finally, part of the present invention using the procedure described for the separation or extraction of natural products useful in fields, among others, such as food, chemical, cosmetic and pharmaceutical.

Power ultrasound in food industry processing represents a novel tool, which is becoming increasingly appreciated. The use of ultrasonic energy is very promising because it can act without affecting the main characteristics and quality of the products. This work investigates the kinetics of ultrasonic dehydration processes of vegetables by direct contact vibrator-product. To that purpose, a parametric study of the relative influence of the main physical parameters involved in the process has been carried out. A specific experimental set-up has been designed, developed and tested. Trials were carried out with potatoes and apples. A 20kHz resonant transducer was designed with the aim to obtain high-amplitude displacements. Assessment of the properties of the samples (residuary moisture content and viscoelastic constants) is obtained from the analysis of high frequency (0.5-1MHz) wideband ultrasonic signals transmitted through the samples by using air-coupled transducers. The dehydratio...

During severe accidents of nuclear power plants radioactive material can be released from fuel and form aerosols that, even though highly unlikely, might reach the environment. There exist a number of systems to mitigate any potential emission from a nuclear power plant and, in particular, what is known as Filtered Containment Venting System (FCVS). After the Fukushima accident some investigations have been launched to boost the efficiency of those systems as much as possible under any foreseen conditions. This work deals with an experimental study about the potential application of a power ultrasonic system as an innovative approach to precondition the particle load reaching the first filtration stages of the FCVS. This study includes the design and acoustic characterization of an ultrasonic agglomeration chamber at 21 kHz in which a high intensity standing wave field is established. This system has been tested with SiO2 aerosols of diameters of 0.3 μm, 1 μm and 2.5 μm, and polydis...

Power ultrasound application on convective drying of foodstuffs may be considered an emergent technology. Acoustic energy may improve drying rate without significantly heating the material due to phenomena affecting mass transfer resistances. As a consequence, ultrasound application on the drying of heat sensitive materials or in process carried out at low temperatures is quite interesting. The aim of this work was to address the influence of the main processing variables on the convective drying assisted by power ultrasound (21.7 kHz) of different foodstuffs. The influence of air velocity and temperature, raw material characteristics, mass load density and ultrasonic power applied was addressed. From the experimental results, a significant influence of the application of power ultrasound on both external and internal resistance to mass transfer has been found. Nevertheless, the ultrasonic effects depended strongly on the experimental conditions used. In the case of carrot drying at...

Aerosol particles inside a high-amplitude ultrasonic field can experience an agglomeration process that causes their size distribution to be changed. The overall effect of this process can be measured by the particle diameter growth, in terms for instance of the Aerodynamic Count Median Diameter (ACMD). However, the analysis of a poly-dispersed particle mixture requires a complex evaluation of the aerosol size distribution. In this work a method consisting on fitting the measured aerodynamic particle size distributions by lognormal functions is proposed. The aerosols used in the experiments were composed by SiO2 particles of different sizes: 0.3 μm, 1 μm, and 2.5 μm, with different concentrations and exposed to a intense ultrasonic standing wave field with an average sound pressure level of about 155 dB and a frequency of 21 kHz.

Ultrasonics processing is becoming an increasily attractive field due to the sustainable character of the use of ultrasonic waves: low energy consumption and no contaminating processes. However the applications of ultrasonic energy in fluids, and more specifically in gases, have been limited for the difficulty to generate efficiently such energy in large scale processes. To overcome this problem a new family of ultrasonic generators with extensive radiators were developed during the last years. Such new generators opened possibilities to study and implement new processes in fluids at industrial level. This paper deals with the characteristics and performance of some new sonoprocesses in gases and multiphase media developed at industrial and/or semi-industrial level for environmental and industrial applications.

6 pp.-- PACS nrs.: 43.25.-x; 43.35.-c.-- Comunicacion presentada en los siguientes congresos: II Congreso Iberoamericano de Acustica. XXXI Congreso Nacional de Acustica – TecniAcustica 2000. II Jornadas Iberoamericanas de Ultrasonidos. II Congreso Iberico de Acustica. EAA Symposium on Architectural Acoustics (Madrid, 16-20 Octubre 2000).

Mass transfer processes in supercritical fluid extraction (SFE) can be enhanced by power ultrasound. This is probably the unique practical way to produce a deep agitation under the high-pressure conditions of SFE because the use of mechanical stirrers is unable on an industrial scale. For the generation of the ultrasound a 20kHz sandwich-type piezoelectric transducer for a power capacity of about 100W was designed, constructed and characterized. To drive and keep it at resonance during the trials, a specific electronic system was developed. This system permits to generate constant output power in the fluid under conditions ranging from the normal gas regime (1bar and 20oC) up to the supercritical regimen (280bar and 55oC). The feasibility of the ultrasonic technology to assist supercritical extraction processes was demonstrated in almond oil extraction where improvements of about 30% in the kinetic of the process were reached. Introduction Ultrasonic energy is a tool with a wider ap...

Industrial processes assisted by high-power ultrasound (HPU) have become an attractive field for industries because of its sustainability (low energy consumption, non-pollutant processes). These processes are based on the proper exploitation of the non-linear effects associated to finite-amplitudewave propagation that are able to enhance mass transfer processes in food dehydration. The main objective of this work is the analysis of the acoustic field, generated by a high power ultrasonic transducer with circular radiator confined in a drying chamber, and obtained by numerical methods; as well as the parametric study of the sample location inside the chamber, in order to optimize the system efficiency.

8 pages, 8 figures.-- Comunicacion presentada en: XXXV Congreso Espanol de Acustica – TecniAcustica 2004, IV Congreso Iberoamericano de Acustica, IV Congreso Iberico de Acustica y EAA Symposium "Environmental and Architectural Acoustics" (Guimaraes, 14-17 Sep 2004).

Industrial processing assisted by high-power ultrasound has become an attractive field for industries due to its sustainability (low energy consumption, non-pollutant processes). In order to obtain the desired effects, the high power ultrasonic transducers have to work properly, vibrating at the desired frequency and achieving high values of displacement with a minimum mechanical stress in its different parts (Langevin type vibrator, mechanical amplifier or horn, and plate radiator). The horn is the part of the transducer where the highest displacement amplification takes part, and also the place where the highest mechanical stresses occur, mainly in the connection point with the plate radiator and in the junction of the two different sections. The objective of this work is to show the behaviour, obtained by numerical methods, of a rectangular plate transducer when different shapes of mechanical amplifiers are designed.

The signal-to-noise ratios (SNR) of ultrasonic imaging and non-destructive evaluation (NDE) applications can be greatly improved by driving each piezoelectric transducer (single or in array) with tuned HV capacitive-discharge drivers. These can deliver spikes with kW pulsed power at PRF ≈ 5000 spikes/s, achieving levels higher even than in CW high-power ultrasound: up to 5 kWpp. These conclusions are reached here by applying a new strategy proposed for the accurate modeling of own-design re-configurable HV capacitive drivers. To obtain such rigorous spike modeling, the real effects of very high levels of pulsed intensities (3–10 A) and voltages (300–700 V) were computed. Unexpected phenomena were found: intense brief pulses of driving power and probe emitted force, as well as nonlinearities in semiconductors, though their catalog data include only linear ranges. Fortunately, our piezoelectric and circuital devices working in such an intense regime have not shown serious heating prob...

This paper in memory of Leif Bjorno deals with the non-linear acoustic problems linked to high-intensity ultrasonics, an area that he deeply cultivated. The generation, propagation and measurement of high intensity ultrasonic waves in air is highly conditioned by the nonlinearities that are inherent with high intensities such as wave distortion and saturation. Particularly in air the propagation of high-intensity ultrasonic waves is greatly affected by the strong non-linearity introduced by the medium itself which notably limits the attainable acoustic pressure levels. On the other hand the power capacity of the sources is also limited by nonlinear effects such as modal interactions and fatigue failure of its components. Finally, the characterization and measurement of the acoustic field of finite amplitude waves by means of probes of very small diameter with respect to the wavelength poses specific issues on the signal capture and the distortion introduced by the probe itself. All these problems will be reported and analyzed in this paper in light of the experimental work developed, partly on collaboration with Leif Bjorno.This paper in memory of Leif Bjorno deals with the non-linear acoustic problems linked to high-intensity ultrasonics, an area that he deeply cultivated. The generation, propagation and measurement of high intensity ultrasonic waves in air is highly conditioned by the nonlinearities that are inherent with high intensities such as wave distortion and saturation. Particularly in air the propagation of high-intensity ultrasonic waves is greatly affected by the strong non-linearity introduced by the medium itself which notably limits the attainable acoustic pressure levels. On the other hand the power capacity of the sources is also limited by nonlinear effects such as modal interactions and fatigue failure of its components. Finally, the characterization and measurement of the acoustic field of finite amplitude waves by means of probes of very small diameter with respect to the wavelength poses specific issues on the signal capture and the distortion introduced by the probe itself. All these problems will be ...

The application of high‐intensity acoustic fields to an aerosol can produce the agglomeration of the suspended particles, shifting their size distribution to a large range. Acoustic agglomeration is a process in which acoustic forces cause particles to interact and eventually to collide. The complex mechanism of this process involves orthokinetic and hydrodynamic effects. The orthokinetic effect refers to direct collisions produced among particles of different size and/or density which are differently entrained by the acoustic field. The hydrodynamic effects refer to particle interactions generated through the surrounding fluid by hydrodynamic forces induced by the acoustic field. One important hydrodynamic effect is the acoustic wake effect which is related to the asymmetry of the flow field around the moving particles. Acoustic agglomeration has a potential use in the separation of fine particles (smaller than 2.5 μm) which are emitted from industrial and residential combustion and from vehicle exhaust....

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 ...

Supercritical fluid extraction (SFE) is a recent technology that is based on the solvent power that some fluids exhibit under pressure and temperature above certain values named as critical point. This process, using supercritical CO 2 as solvent, has gained wide acceptance in the last years, because of its advantages compared to conventional solvent extraction ones. Nevertheless one of the difficulties of SFE is to achieve favourable kinetics due to the fact that mechanical stirring is not easily applied to an extractor vessel operating at high pressures. An interesting alternative is the use of power ultrasound (HPU). Ultrasonic radiation represents an efficient way to enhance mass transfer processes, because of mechanisms such as acoustic streaming, turbulence, radiation pressure, compressions and decompressions in the material, heat and/or cavitation.

In recent years, the application of numerical methods in engineering and in particular in the design of piezoelectric transducers, has supplied a tool with great potential for optimization and development of new high intensity ultrasonic transmitters for industrial applications. These issuers have a complex structure combining extensional to flexural vibrations. Basically radiators consist of extensive surface and phased-ribbed profile, excited at its center by a piezoelectric vibrator compound. These systems are designed for radiation transduction in fluids with high efficiency (η) and high quality factor (Q), which implies a very precise tuning of its components. This high tuning can be achieved with finite element modeling where such modeling was carried out with a precise and proven methodology.

This study evaluated the effect of drying temperature and ultrasound application in the antioxidant activity of dried peel of passion fruit. Drying experiments were carried out at four air temperatures (40, 50, 60 and 70ºC) without and with ultrasound (21.7 kHz, 75W) application. The antioxidant capacity (AC) and the total phenolic content (TPC) of dried samples were assessed. Highest temperatures and ultrasound application significantly reduced drying time. Both factors affected the AC and TPC of dried samples. Thus, at 40 and 50 ºC the ultrasonically assisted dried samples showed higher AC and TPC than the conventionally dried ones.

The main aim of this work was to evaluate the application of power ultrasound on the drying of salted cod at low temperature. For that purpose, drying experiments of salted cod slabs (length 50 x width 30 x thickness 5 mm) were conducted in a convective dryer with air recirculation, temperature and air velocity control, and an ultrasonically activated drying chamber. Air-drying (AIR) and ultrasonically assisted air-drying (AIR+US, 20.5 kW.m-3) experiments were carried out at -10, 0, 10 and 20°C at constant air velocity (2±1ºC m.s-1) and relative humidity (9±4%). A diffusion model was used in order to quantify the influence of ultrasound in drying kinetics. Drying rate increased as air temperature was higher. At all temperatures tested, ultrasound application increased the drying rate, achieving drying time reductions between 35 and 50% by ultrasound application. The diffusion model considered described adequately the drying kinetics. The application of high power ultrasound increase...

Removing very fine particles in the 0.01-1 micro m range generated in diesel combustion is important for air pollution abatement because of the impact such particles have on the environment. By forming larger particles, acoustic agglomeration of submicron particles is presented as a promising process for enhancing the efficiency of the current filtration systems for particle removal. Nevertheless, some authors have pointed out that acoustic agglomeration is much more efficient for larger particles than for smaller particles. This paper studies the effect of humidity on the acoustic agglomeration of diesel exhausts particles in the nanometer size range at 21 kHz. For the agglomeration tests, the experimental facility basically consists of a pilot scale plant with a diesel engine, an ultrasonic agglomeration chamber a dilution system, a nozzle atomizer, and an aerosol sampling and measuring station. The effect of the ultrasonic treatment, generated by a linear array of four high-power stepped-plate transducers on fumes at flow rates of 900 Nm(3)/h, was a small reduction in the number concentration of particles at the outlet of the chamber. However, the presence of humidity raised the agglomeration rate by decreasing the number particle concentration by up to 56%. A numerical study of the agglomeration process as a linear combination of the orthokinetic and hydrodynamic agglomeration coefficients resulting from mutual radiation pressure also found that acoustic agglomeration was enhanced by humidity. Both results confirm the benefit of using high-power ultrasound together with humidity to enhance the agglomeration of particles much smaller than 1 micro m.