A simple mathematical description of jet nebuliser performance

A simple mathematical model describing some aspects of jet nebuliser performance has been applied to three commercial medical jet nebulisers. The model gives the nebuliser efficiency E, defined as the volume fraction of water released as an aerosol or lost by evaporation, and the nebulisation time T, as functions of the initial volume of water V o. Model parameters include the volume flow rate q o of water to the nebulisation region and the fraction η of aerosol intercepted by the baffle and internal walls of the nebuliser. The model identifies an initial phase of nebuliser operation of duration T 1 during which nebuliser output is at a constant continuous rate and a subsequent intermittent phase. Two residence times τ 1, τ 2 are used in the model: τ 1 is the residence time associated with the rapid recycling of the majority (a fraction η 1) of the aerosol deposited on the walls while τ 2 is the longer residence time associated with the remaining fraction 1- η 1. Comparison between experiment and model predictions suggest broad agreement, though the model tends to underestimate T at low V o, possibly due to oversimplification of the intermittent phase description.