Ultrasonic irradiation devices

As noted above this type of mechanical transducer is predominantly used for homo-genisation/emulsification. These devices differ markedly from the more usual bath and probe types in that they derive their power from the medium (by mechanical flow across the blade) rather than by the transfer of energy from an external source to the medium. The majority of the chemical effects observed on using whistle type transducers for the sonication of homogeneous reactions can be attributed mainly to the generation of very fine emulsions rather than the ultrasonic irradiation itself. 

Li et al. [100] studied the blends of HOPE and PA6 prepared by ultrasonic extrusion. The extruder set-up, equipped with a capillary die and an ultrasonic device, is shown in Figure 8.27. Ultrasonic irradiation led to the degradation of polymers and in-situ compatibilization of blends, as confirmed by variations in complex viscosity, storage modulus and loss modulus. The relationship between storage modulus and loss modulus indicated the effect of ultrasonic irradiation on the compatibility of HDPE/PA6 blends. Theoretically, in the linear viscoelastic region (co O), the G and G" of compatible polymer blends have the following relationship ... 

So far, a number of examples are known for the ultrasonic irradiation of fluids in microstructured devices for a broad variety of applications, for example, active micromixing and emulsiflcation [22], transport and/or separation of particles, substances, or cells [23], against clogging [24], and for synthetic applications [25]. 

Industry uses special devices similar to ultrasonic baths and probes but appropriately scaled up in size and ultrasound irradiation power. The UIP16000 model from Hielscher Ultrasound Technology is by far the most powerful ultrasonic processor available worldwide the apparatus is capable of delivering a continuous power of 16000 W at efficiency above 80%. Such powerful systems have been developed in response to the demand for the ultrasonic treatment of liquids on a large scale in fact, the ultrasound power required usually increases in proportion to the amount of liquid to be treated within a certain time. 

It is often difficult to compare the sonochemical results reported from different laboratories (the reproducibility problem in sonochemistry). The sonochemical power irradiated into the reaction system can be different for different instruments. Several methods are available to estimate the amount of ultrasonic power entered into a sonochemical reaction, the most common being calorimetry. This experiment involves measurement of the initial rate of a temperature rise produced when a system is irradiated by power ultrasound. It has been shown that calorimetric methods combined with the Weissler reaction can be used to standardize the ultrasonic power of individual ultrasonic devices. ... 

The irradiation time is highly dependent on the power of the ultrasonic device. A color change of the reaction mixture from orange-brown to deep purple indicates reduction of the diphosphene to the corresponding anion radial. If this occurs, the flask should be removed from the ultrasonic bath. Addition of few drops of MeOH restores the orange color. 

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