BASIC NEBULIZER FUNCTION

The main function of a jet nebulizer is to aerosolize the contained li quid. The primary generation point is the orifice where the compressed air expands and increases in velocity. At this point the expanding ai r induces an underpressure and liquid is sucked up to the air orifice where it meets the rapidly expanding air. Droplets from the liquid sur face are carried away with the airstream towards the baffle system. Af ter cut-off by impaction on the baffle surface, secondary generation o ccurs 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 li quid output and droplet size distribution. There is also disparity bet ween individual nebulizers of the same brand. This is due to manufactu ring errors. Repeated use of a single nebulizer over time causes agein g. This, in turn, causes the critical points of droplet generation to change. The most significant changes are the small increases in the di ameter 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 t he output characteristic of the nebulizer. With decreasing driving pre ssure the air velocity decreases. This in turn, increases the droplet size generated at the air orifice. To maintain stable generation condi tions the driving pressure should be kept constant despite the resulti ng increase in volumetric flow rate.