Droplets Produced by Medical Nebulizers: Discussion (Part 1)

The fact that the nebulizer solution temperature of jet nebulizers falls during generation has been well documented. The heat loss is due to the evaporation of the nebulizer solution to saturate the gas used to generate the aerosol and some cooling due to adiabatic expansion of the generating gas. This evaporation also leads to an increase in solute concentration of the nebulizer solution. The gas from a compressed gas cylinder contains no water vapor, while an air compressor supplies air of ambient humidity. Less vapor is therefore required from the nebulizer solution to saturate the air from an air compressor and heat loss is therefore reduced. Of the energy imparted to the solution of an ultrasonic nebulizer, however, part is used to overcome the surface tension to disperse solution droplets and part to heat the solution itself. The nebulizer solution therefore warms during generation (Fig 2). ventolin inhaler

The initial output from the nebulizer depends on the type, the flow rate and the saturation of the generating gas. The change in jet nebulizer output measured during generation depends almost solely on the temperature of the nebulizer solution. The nebulizer solution provides both the solution output and the output of vapor necessary to saturate the generation gas with water vapor at the nebulizer temperature. Therefore, the amount of vapor carried by the generation gas decreases as the temperature falls and the reduction in total output mirrors these changes.