Basic Nebulizer Function

Abstract

ABSTRACT

The main function of a jet nebulizer is to aerosolize the contained liquid. The primary generation point is the orifice where the compressed air expands and increases in velocity. At this point the expanding air induces an underpressure and liquid is sucked up to the air orifice where it meets the rapidly expanding air. Droplets from the liquid surface are carried away with the airstream towards the baffle system. After cut-off by impaction on the baffle surface, secondary generation occurs on the baffle as droplets are produced due to high air velocity. Several different designs of nebulizer are available. The differences cause variation in the output characteristics; for example, in the liquid output and droplet size distribution. There is also disparity between individual nebulizers of the same brand. This is due to manufacturing errors. Repeated use of a single nebulizer over time causes ageing. This, in turn, causes the critical points of droplet generation to change. The most significant changes are the small increases in the diameter of the air orifice. This may be due to mechanical wear from the compressed air source or to extensive cleaning procedures. The effect of the increasing diameter, as seen by the user, is decreased driving pressure at a constant rate of air flow. There is also an effect on the output characteristic of the nebulizer. With decreasing driving pressure the air velocity decreases. This in turn, increases the droplet size generated at the air orifice. To maintain stable generation conditions the driving pressure should be kept constant despite the resulting increase in volumetric flow rate.