Abstract
In this paper the basic theory for the efficiency of air cleaners and filters is developed. The intrinsic efficiency is a characteristic of the filter and conditions of operation, is independent of the size composition of the entrained dust, and is expressed by a graph of collection efficiency for individual particle sizes. Knowledge of the intrinsic efficiency of a filter enables the mass efficiency of collection to be calculated for any given size composition of dust burden.
A full description is given of the characteristics of natural airborne dusts, and of research which led to the formulation of a standardized test dust for cleaners and filters for the air supply to internal-combustion engines. The test dust specification for this purpose was adopted by the Ministry of Supply, and subsequently incorporated in British Standard 1701: 1950. Notes on the method of examination of dusts are included.
The object of the specification is to ensure that the test dust contains some of all particle sizes that are likely to be encountered in the practical operation of vehicles and aircraft. Furthermore, the particle size distribution in the test dust should be uniformly graded from the maximum to the minimum size.
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