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A lower noise alternative for compressed air drying

The problem

Air knives diagram

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.

The solution

Air flows diagram

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.

The cost

About £900, plus installation. (1995)

The result

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.

Source

Report supplied by Meech Exair.

Updated 2010-04-02