Collison Nebulizer Droplet Number Output

This describes a numerical analysis of the Collison nebulizer to determine the total number of droplets produced for a given back pressure and the count within 2 standard deviations of the mean droplet size (assuming a log-normal distribution).

The Collison nebulizer can be operated with a variety of “jet” numbers depending on the attachment. Each jet requires approximately 2 Lpm of air and produces droplets with an MMAD of 2.5 µm with a GSD of 1.8. The comparable CMAD is 0.89 µm.

As given in the table below, the amount of liquid in the nebulizer reservoir used per hour per jet varies depending on the back pressure applied to the nebulizer which can be computed with the following equation:

To determine the number of droplets produced per jet per hour by the Collison, a resulting log-normal distribution of droplet sizes was assumed. The central concept used to determine the number of droplets produced by the Collison is that the liquid volume contained in the total of all droplets produced must be equal to the volume of liquid produced by the Collison on a per time basis.

A spreadsheet was constructed with 600 diameters ranging from 0.05 µm to 20 µm in even increments on a log-basis (-3 to 3 by every 0.01 ln values). The frequency of occurrence of each diameter was computed with the use of the probability distribution function for a log-normal distribution. The volume associated with each diameter was computed using the equation for the volume of a sphere. The “Solver” function in Excel was then used to determine the counts for each diameter that caused the sum of all volumes (for each diameter) to be equal to the volume generated per hour (as per the equation above) while weighting the count for each diameter by their computed frequency of occurrence. From the total number, the count between
+/- 2 standard deviations of the mean was calculated. The results given in the table below were converted to a per minute basis and include the liquid output for a single jet as well as the estimated counts for a single, 3, 6, and 24 jet Collison.

The basis of the table is available for viewing