How to Save Your Air Wiping Cost

An air wipe converts the potential energy of compressed air into kinetic energy by forcing the air through constricting orifices. Its performance is governed by 2 physical equations, namely:

          1. K. E. = ½ Mv² ...……    Equation of Kinetic Energy
          2. A1v1 = A2 v2   ……….   Equation of Continuity

where:   M = mass, which in an air wipe is the amount of air flow
              v = velocity of the air
             A = cross sectional area

The equation of Kinetic Energy (K. E.) reveals that K. E. is proportional to 1: 1 of the air flow but to square of the air velocity in an air wipe. For a twofold increase in air supply, the K. E. will increase merely by a factor of 2, while your cost of compressed air doubles. However, if you manage to raise the air velocity by twofold, the K. E. will upgrade by a factor of 4. No additional cost is involved.

This can be done by manipulating the equations. The Equation of Continuity can be re-written as follows:

          3. v2 = v1 ( A1/A2)

where in the case of an air wipe:

          v2 = air velocity in the constricting orifice
          v1 = air velocity in the air supply hose
          A2 = area of the constricting orifice
          A1 = area of the air supply hose

By substituting equation 3 into equation 1, you have:

          4. Kinetic Energy = ½ M (v1)² (A1/A2)²

this reveals that if M, v1 and A1 remain constant in an air wipe, the K. E. is inversely proportional to the square of the constricting orifice. In other words, you can upgrade the performance of your air wipe by reducing the cross sectional area of the individual orifices.

However, in practice, there are limitations. For instance, there is a lower limit to the cross sectional area of the individual orifices, particularly when working with air wipes made of ultra-hard material. Furthermore, it takes many smaller orifices to pass the same amount of air that goes through a larger orifice. In the end, it’s a matter of compromise in air wipe design on which you as the end-user is not involved with.

Your can opt to compare among air wipes to select an air wipe which delivers the maximum air velocity with the least amount of air consumption.

The 2nd measure is totally under your command.

Even after the air leaves the constricting orifice and enters the wiping cylinder of the wire wipe, it still behaves according to the Equation of Continuity. It now reads:

          5.                     v3 = v2 (A2/A3)

where v3 and A3 stand for air velocity in the wiping cylinder and its effective cross sectional area respectively. This cross sectional area is equal to:

        A3 = Area of the wiping cylinder – Ø of the wire = The Gap

That is to say:

V3 is inversely proportional to the cross sectional area of the gap or, the narrower the gap, the higher the air velocity, which translates into a higher efficiency air wipe with less air consumption.

Therefore it’s your move on how to maintain the narrowest possible gap between the wire and the air wipe (that is, the wiping cylinder), while taking into account the + manufacturing tolerances or the upper spec that must be added to the nominal wire Ø, to avoid wire jamming. For the lower limit of the gap, please see "Gap Dimension Governs Air Wipe Performance."

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Gap Dimensions and Performance Supersonic Air Wipe