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Quieter by design - air knives

The problem

Many manufacturing processes use air 'curtains' for drying, film control and product wiping. The air knife, for example, consists of a tubular plenum chamber stretching across the width of the product line, with a slot along its length. Air is supplied to the plenum at high pressure and leaves the slot as a high velocity 'blade' of air directed to strike the product line passing below.

A-weighted noise levels of between 90 and 95 dB can be generated by a conventional multi-jet system supplied with air from belt-driven, single-stage blowers.

The solution

The use of a long continuous single jet rather than multiple individual jets can decrease velocity, thus reducing noise output from the jet itself. Jet noise can be further reduced if the air supply plenum is designed to have an aerodynamically smooth approach to the blade nozzle entry.

One manufacturer of this type of dryer used two direct-drive, multi-stage, centrifugal blowers for the air source to produce a flow of some 112 litres per second and a static pressure of up to 16 kilopascals (KPa).

Cross-section of an air knife

Air knive diagram

Use of single jet

Usage of a single jet diagram

The cost

About £2000. (1995)

The result

A noise reduction of about 15 dB at 3 m.

Source

Equipment supplied by Air Control Installations (Chard) Limited.

Updated 2010-04-02