Forschungs- & Entwicklungsinformationsdienst der Gemeinschaft - CORDIS

Properties of various electrostatic air cleaning techniques (electrostatic precipitators, electret fliters and electified fibrous filters). Efficiency. Humidity effects. Loading characteristics.

The performance studies of commercially available cabin air filters were supplemented with laboratory studies on various electrostatic air cleaning techniques. Measurements were made with
- electrified fibrous filters
- electret filters (together with a corona charger)
- electrostatic precipitators

The experiments with the electrified fibrous filter (i.e. a fibrous filter exposed to an external electric field) indicated that an improvement of efficiency can be achieved in dry conditions. However, the combination of a contaminated filter material and high air humidity causes a significant degradation of efficiency. Thus, this technique was excluded from the further considerations.

The combination of the corona charger and an electret filter was found to provide quite good filtration performance. This system seemed to perform quite well also in the laboratory loading test, i.e. efficiency of the filter exposed to simulated test aerosol (diesel fume and ISO Coarse test dust) remained at a reasonable level. Laboratory experiments may, however, produce too optimistic picture about the performance, because the high concentration of electrically charged loading test aerosol generates strong electric fields, which will not occur in normal operation conditions. It seems that determining the true performance of corona charger & electret filter requires extensive field studies.

The experiments with cigarette smoke indicated that a significant degradation of electret filter efficiency took place, i.e. relatively low amounts of cigarette smoke caused a strong efficiency decrease. Thus, it seems that electret filters are unsuitable for conditions where filter becomes exposed to cigarette smoke. There is also some evidence that similar behaviour is observed when electret filter is exposed to fine combustion aerosol. Thus, it is very questionable if the good efficiency of the corona charger & electret air cleaning system could be maintained at all operation conditions.

The properties of the electrostatic precipitators were studied by using two commercially available devices and with two-miniature laboratory prototypes prepared for CLEANRCAB purposes. The results indicated that high efficiency for fine particles could be achieved with moderate pressure drop level. Also, it was observed that good efficiency could be achieved with the compact or miniature electrostatic collectors.

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