Compressed air jets, widely used in industry for drying, can emit excessive levels of noise from the high jet discharge. One manufacturer measured A-weighted noise levels of 96 dB at operator positions coming from a bank of plain-ended, 6 mm diameter copper pipes being used to dry small components emerging from a washer on a conveyor line.
Noise reduction was achieved by replacing the plain jets with induced-flow type air knives. This followed the aerodynamic principle, known as the 'Coanda Effect', by which an air stream discharged at high velocity immediately next to a surface attaches itself to that surface and follows its contour.
In this case the contour was a rounded corner of a metal block. The effect of discharging the jet along one face was to produce a high velocity air flow along the other face at right angles to it. The air then left the second face to become a high-velocity free-stream flow directed at the washer conveyor line.
The primary flow was drawn along with a secondary flow from the still air through which it passed, so reducing the noise-generated turbulence. Primary air consumption was also reduced, resulting from the more efficient movement of secondary air.
A noise reduction of 9 dB. The company has since reported a four week cost recovery on the installation and overall annual savings of some £6000 on the cost of compressed air production.
Report supplied by Meech Exair.