Modelling MDI Spray

The spray ejected from a pressurised canister has the potential to influence a lot of aspects of the inhaler design; spacer shape, size, material, nozzle design, disassembly for cleaning, etc.

To quickly model the ejected particle behaviour of Salbutamol Sulfate (the medicine used in Ventolin inhalers), we designed a simple experiment;

MDI Spray Modelling

In this experiment, the inhaler is repeatedly sprayed directly at several sheets of paper (or panes of glass), with the distance between the inhaler and the sheet increasing by a set increment each time. This should provide several cross-sections of the ejected spray, which can then be used to gauge its overall shape.

Because Salbutamol Sulfate is a fine white powder, it is hard to identify on any surface except at very close ranges. We tested the spray on matte black, white and transparent surfaces with little success. So to try and isolate the spray from its corresponding surface, we shone an Ultraviolet light on it. Many white particles and surfaces fluoresce under UV light...

Inhaler residue on black, white and glass

Residue under UV light

Unfortunately, Salbutamol Sulfate is not one of them.

Experiments are a necessary component of the design process, and a negative result can still prove to be enlightening. This time, however, we had to search for alternative sources of information...