Cavitation contact ultrasound

An interesting way to retard catalyst deactivation is to expose the reaction mixture to ultrasound. Ultrasound treatment of the mixture creates local hot spots, which lead to the formation of cavitation bubbles. These cavitation bubbles bombard the solid, dirty surface leading to the removal of carbonaceous deposits [38]. The ultrasound source can be inside the reactor vessel (ultrasound stick) or ultrasound generators can be placed in contact with the wall of the reactor. Both designs work in practice, and the catalyst lifetime can be essentially prolonged, leading to process intensification. The effects of ultrasound are discussed in detail in a review article [39]. 

Reason Initial fast reaction of Zn metal with acid decreases due to a thin oxide coating on the surface of the metal, hindering the further intimate contact of metal with acid. However, when the solution flask was immersed in the ultrasonic cleaning bath, the surface of the metal is cleaned by the agitation generated due to mechanical vibration and acoustic cavitation, exposing the fresh metal surface for reaction with the acid. As a secondary effect of ultrasound, the H2 gas bubbles... 

Direct contact of the body with liquids or solids subjected to high-intensity ultrasound of the sort used to promote chemical reactions should be avoided. (In contrast, ultrasound used for medical diagnostic imaging is relatively benign.) Under sonochemical conditions, cavitation is created in liquids, and it can induce high-energy chemistry in liquids and tissues. Cell death from... 

In contrast, contact as well as airborne ultrasound application avoids the occurrence of external cavitation and thus reduces the risk of related effects such as radical formation and oxidation. Thus, to the present author s knowledge, no important quality impairment due to such ultrasound-assisted processes has yet been reported. Soria et al. (2010) found only minor changes in the reducing sugar... 

In these studies, we used unfocused ultrasound with a frequency of 0.88 MHz and an intensity of 2 W/cm. Cavitation properties of gels containing impurities and without them were comparatively estimated using an IS-3 MS cavitation indicator developed at the Belarusian State University of Informatics and Radioelectronics. The device s operating principle is based on the measurement of the level of scattered noise in a frequency band from 2 to 10 MHz, received by a broadband hydrophone. An emitter 2 cm in diameter was in direct contact with the face of the cylindrical gel sample (2 cm high and 2.5 cm in diameter), that is, measurements were performed in the transducer s near field. The hydrophone with a sensitive element 2 mm in diameter was placed in the immediate vicinity from the side surface of the sample. 

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