Ultrasound process variables

Garda-Perez, J. V., Carcel, J. A., Benedito, J., Riera, E., Mulet, A., 2007. Influence of process variables on hot air drying assisted by power ultrasound. Proceedings of 19th International Confess on Acoustics, Madrid. 

Thus, it can be concluded that the correct design of an ultrasonic system (generator, transducer and application systems) represents a key step towards the efficient application of ultrasound, and generates significant effects in drying. However, it is also extremely important to appreciate the influence that different process variables have on the levels of drying intensification linked to ultrasound application these aspects are addressed in the next section. 

Influence of the Main Process Variables on Drying Intensification by Ultrasound... 

Digestion. The influence of ultrasound on the dissolution kinetics of phosphate rock in HNO3 solutions [11] and variables affecting it (viz. particle size, reaction temperature, acid concentration, amplitude of US power) were studied by Tekin [12]. The term dissolution in the presence of auxiliary energy and an acid seems inappropriate in this case as the process is more like a true digestion. Another case in point is the dissolution of pyrite ores in acid and Fe2(S04)3 solutions, which is improved by 30% with respect to the absence of US energy [13]. 

The credibility of the hot spot theory is reinforced by its ability to account for the effects of extrinsic variables on the sonochemical process. Nevertheless, the frequency of ultrasound applied is surprisingly irrelevant to the course of the reaction. Cleaning baths produce a range of frequencies which often vary from day to day, or even during the course of a reaction, and yet this has no discemable effect on the sonochemistry observed. 

Clearly, a large number of variables - including product and process characteristics -are involved when ultrasound is applied with the aim of intensifying the drying, and hence it is difficult to draw general conclusions. For these reasons, the influence of the most important variables is addressed in the following subsections, and illustrated with examples of applications. 

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