Efficiency dust spot

Efficiency, dust spot The capability of a filter to remove the staining portion of atmospheric dust from a gas under set test conditions, expressed as a percentage. 

EN 779 1993 in principle contains two different test methods. The filter is tested both with untreated outdoor air and with the addition of synthetic dust. In the first case, the filter s dust spot efficiency is determined, i.e., its capacity to clean normal outdoor air. In the second case, the filter s arrestance is measured, i.e., its capacity to separate synthetic dust. The average value for dust spot efficiency or arrestance during the course of the test is used for classification of the filter. 

In EUROVENT 4/9 the dust spot efficiency has been replaced by measurement of the degree of separation of particles within the 0.2-3 pm range, with a particle size of 0.4 pm used for classification of the filter. 

Fine filter, 0.4 im efficiency Fine filter, dust spot efficiency Average ( ) efficiency, % ... 

To be classified as an F-filter, EN 779 requires that the dust spot efficiency for new filters be greater than 20%, whereas Eurovent 4/5 has no such requirement. 

Atmospheric dust spot efficiency A test to measure the extent to which a filter paper is soiled after dust-laden air has passed through it. 

This forms the basis of Eurovent 4/5. There are two tests. The atmospheric dust spot efficiency test, assessing the... 

AFI Dust Spot Efficiency [Atin ospheric Dust) ... 

BS 6540 (Pt 1) 1985 Methods of test for atmospheric dust spot and efficiency, and synthetic dust weight arrestance HSE Guidance Notes, HMSO, London MS 13 Asbestos (1988)... 

The determination of atmospheric dust spot efficiency is a staining test, described in detail in BS EN 779, and used for AC and ventilation filters. It is based on the intensity of staining of a target ultrafine filter paper caused by the flow through it of a quantity of dusty air. The intensity of staining is measured by an opacity meter, and provides an empirical measurement of the concentration of contaminant in the air stream. In the filter test, the downstream air flows constantly through its collection paper, while the upstream air is sampled for only a proportion of the time (because of its much higher dust concentration), and this proportion is controlled to yield an equivalent stain to that from the downstream flow. The flow ratio can then be converted to a filtration efficiency. 

These classifications are considered to be a proven method for designing air filtration media according to average synthetic dust weight arrestance and average dust spot efficiency, although it should be slated that the whole test situation is complicated by not only the diverse test procedure but the diversity of particulate materials specified for them. 

If the only cause of dust-particle detachment were the ionic wind, the efficiency of particle removal should increase with increasing electrode potential. This however, is not in accord with the actual facts (Fig. VII.5). With relatively small distances between the electrode and the treated surface (1-3 mm), the clean spot diameter increases as the electrode potential is increased up to 3.2 kV, but further increases in potential fail to produce any increase in the clean spot... 

The efficiency of the operation of the ac electric field was estimated by reference to the area, or rather the diameter, of the sharply defined dust-free spot formed on the grounded surface opposite to the detaching electrode. 

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