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Forced air drying assisted by air-borne ultrasound has been developed by applying stepped-plate ultrasound generators. Another procedure has been developed and tested in which the ultrasonic vibration is applied in direct contact with the vegetable samples and together with a static pressure. The good acoustic impedance matching between the vibrating plate of the transducer and the food material favours the deep penetration of acoustic energy and increases the effectiveness of the process. The vegetable is subjected to high ultrasonic stresses which, due to the rapid series of contractions and expansions, produce a kind of "sponge effect" and the quick migration of moisture through natural channels or other channels created by the wave propagation which result in moisture release from the product. In addition, the production of ultrasonic cavitation inside the liquid may help to the separation of the moisture strongly attached.
The drying effect remarkably improves with respect to the forced-air drying (with and without air-borne ultrasound). In fact, the dehydration process is not only quicker and less energy consuming but it is more powerful: the final moisture content could be less than 1%. In addition, due to the processing time and low temperature of the air flow, the product qualities are very well preserved.
Removal of fine particles (smaller than 2.5 microns) from industrial flue gases is, at present, one of the most important problems in air pollution abatement. These particles, which are hazardous because of their ability to penetrate deeply into the lungs, are difficult to remove by conventional separation technology. Sonic energy offers a means to solve this problem. The application of a high-intensity acoustic field to an aerosol induces agglomeration processes which changes the size distribution in favor of larger particles, which are then easier to precipitated with a conventional separator. It consists of an acoustic agglomeration chamber with a rectangular cross-section, driven by four high-power and highly directional stepped-plate transducers of 10 and/or 20kHz.
Another approach to the application of ultrasound in drying and dehydration has been also carried out by using a transducer with a cylindrical radiator inside which a fluidized bed is created .The product to be dried is kept in suspension within such bed which is sonicated in the whole volume by the cylindrical radiator of the transducer. Such process has been experimented positively in close cooperation with the Food Technology Department (ASPA Group) of the Polytechnic University of Valencia.
The procedure is based on the use of ultrasonic energy for washing flexible solids such as textiles. It is specially adequate for continuous washing of materials with an extended surface, (i.e., wiht shape of band, strip, sheet) and/for single pieces which can be placed on conveyor belts or similar transporting elements. The ultrasonic energy is applied to the textiles to be cleaned through flexional vibrating plates in direct contact or very close to the material to be washed, which have to be submerged in a thin layer of liquid. This washing process can be completed with an immediat rinse and once out of the liquid, the ultrasonic energy can be applied again by contact to eliminate an important part of the liquid in the washed material, producing a pre-drying effect.
Main advantages with respect to a conventional washing system:
Supercritical fluid extraction assisted by power ultrasound s is a new process based on the application of high-intensity ultrasound to accelerate the extraction effect of supercritical CO2. The new technology has shown to be efficient in a semi-industrial installation Supercritical fluid extraction (SFE) is a separation process based on the contact of a substance containing the extractable compound with a solvent in supercritical conditions. Today, C02 SFE has become a promising technique used in many areas. Some of the motivations for its employment are that the solvent is non-toxic, recyclable, cheap, relatively inert, non-flammable and the process improves product quality and product recovery. Nevertheless, fixed bed SFE of oil from a solid matrix has a slow dynamics even when solute free solvent is recirculated and therefore improvements in mass transfer are required. The use of high-intensity ultrasound represents a potential efficient way of enhancing mass transfer processes. This is due to the effects produced by compressions and decompressions, as well as by radiation pressure, streaming, etc. In addition, this is probably the unique practical way to produce agitation in SFE because the use of mechanical stirrers is unable.
Industrial coatings applied at high speed often contain bubbles from air entrapped during operation. Such bubbles will produce permanent surface defects after drying. Chemical additives are generally used to alleviate the problem, but they are difficult to dose and, if not properly handled, can create problems which may be even worse than the air retention.
High-intensity air-borne ultrasound may be an adequate contact-less method to break the bubbles. The majority of the existing studies about the application of high-intensity ultrasound in coating processes rely on the deaeration of the coating liquid previously to the coating process. Nevertheless, many of the bubbles within the coating layers are produced during the coating application. This work deals with a new process based on the direct application of air-borne ultrasound to break the bubbles which are semi-submerged within the coating layer.
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