Challenge

A low-volume syringe-pump spray system was used to coat a medical-device component. Bubbles were forming within the fluid circuit, resulting in unstable and erratic spray performance. Cavitation was suspected as the source of the problem.

Engineering Approach

The pressure distribution throughout the fluid system was investigated using first-principles mathematical analysis and CFD. The analysis demonstrated that local pressures did not fall sufficiently low for conventional vaporous cavitation to occur, eliminating the initially suspected failure mechanism. Further investigation established that the bubbles resulted instead from gaseous cavitation with dissolved gas coming out of solution as pressure varied within the system. The effect was particularly significant in the acetone-based solvent. A range of potential solutions was then developed and assessed, including alternative valve designs and actuation rates, changes to tubing diameter, control of system baseline pressure and fluid degassing.

Outcome

The underlying mechanism responsible for bubble formation was identified and appropriate modifications were developed and implemented. Bubble formation was eliminated, restoring stable spray performance.