|
|
 |
Scientific news from Division 1 | ||
|
First steps towards a quantitative characterization of ultrasound cleaning vessels |
|||
|
Although ultrasound baths are already in broad use in industry, trade and in the private sector, designing a device for a special purpose has so far required long series of tests and has been based on the individual empirical values of the manufacturers. The reason for this is that the underlying physical effect – cavitation – is, by nature, highly stochastic and depends on a whole series of ambient parameters. Bringing some order into the chaos has now been achieved at PTB. |
|||
|
Ultrasound is used for the most diverse applications in medicine and technology. In liquid media, these are often based on cavitation processes. Due to the stochastic nature and the many influence parameters, it is extremely difficult to check, to control and to optimize all application processes. This hinders especially the manufacturers - who are usually small- and medium-sized companies - from developing and designing ultrasound baths for the broad range of application possibilities. To overcome this problem, a project has been carried out at PTB which was funded via the AiF. The aim of this project was to improve the quantitative description of the processes occurring in ultrasound baths of the small and the medium performance classes with the aid of simple measurements of physical quantities. The most essential approach hereby was the measurement of the sound field quantities. The objective of this project was to develop this approach further and to complement it by new measuring procedures by which the cavitation effects can be determined. For this purpose, different model processes were investigated and suitable indicators for cavitation were developed - among these indicators for the erosion (see Fig. 1), for the chemical effect and for sonoluminescence (see Fig. 2). The indicators serve to describe possible applications quantitatively, and also to determine the actual effect. For this purpose, the relationships of the indicators among each other were investigated and their dependence on the operating parameters determined. An essential element of this was multivariate data analysis. By means of a factor analysis, statistical analyses were carried out and a general procedure was developed by which indicators - or other output quantities of a cavitation process - can be described as a function of easily measurable input quantities (see Figure 3). |
|||
 |
|||
| Figure 1: Cavitation corrosion on an aluminium foil which has been exposed to ultrasound for only a few seconds |
|||
 |
|||
| Figure 2: The bright areas show the chemoluminescence of a sensor placed in the ultrasound bath and the sonoluminescence of the surrounding water |
|||
 |
|||
| Figure 3: Several easily measurable input quantities at the ultrasound cleaning vessel - of which each one for itself does not seem to have any relation to the cavitation effect - can be set together to one fictive quantity which describes the process well. In this example, the water temperature, the sound pressure of the fundamentals and the sound pressure of the cavitation noise constitute a generalized quantity zc which exhibits a good relationship with the erosion effect. |
|||
| Another task was to investigate a filled cleaning bath. For that purpose, representative "workpieces" were selected and a new control of the sensor was developed which takes the position of the workpiece during the measurement into account. It was investigated to what extent the cleaning product changes the sound fields in the bath, and where cavitation takes effect and where not. The methods developed and the results obtained are very helpful for a process description. Cleaning and reaction effects can be estimated quantitatively, and the operating parameters can be optimized. This not only makes it possible for the manufacturers to develop ultrasound baths for a special purpose, but the users also obtain a tool for quality management. The project "Investigation, measurement and optimization of the sound field and its effects in cleaning baths and sonochemical reactors" of the AiF Research Association DECHEMA Society for Chemical Technique and Biotechnology e.V. was funded via the AiF within the scope of the "Programme for the promotion of industrial joint research and development (IGF)" of the Federal Ministry of Economics and Technology. |
|||
| Contact person: | |||
Matthias Jüschke, Dept. 1.6, WG 1.62, E-mail: matthias.jueschke@ptb.de
|