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Questioning Particle Generation Due to Cavitation Erosion as a Source of Contamination

Ultrasonic cleaning is widely used for removing particles from surfaces.  It is generally agreed that the high energy of implosions of cavitation bubbles break the bonds holding particles to the surface being cleaned and that liquid motion (streaming) carries the particles away once they have been dislodged.  However, it is also well known that ultrasonic cavitation and implosion will generate particles as material is eroded from surfaces as cavitation bubbles implode in proximity to them by a process of ultrasonic erosion similar to that seen on a ship's propell

Conductivity Calculations

Previous blogs have talked about heat conductivity in very general terms to produce a foundation for this somewhat more technical view for those of you who like formulas and numbers. Conductive heat transfer can be expressed with "Fourier's Law"
  • q = k A dT / s
  • where
  • q = heat transfer (W, J/s, Btu/hr)
  • A = heat transfer area (m2, ft2)

Heat Conductivity and Convection

Heat conductivity is a measure of the ability of a material to transfer heat within itself.  For example, if you heat one end of a short piece of copper wire, the heat is quickly distributed throughout the wire by conduction.  This can be easily demonstrated using a short piece (1 to 2 inches) of heavy gage copper wire and a small torch or gas lighter.  Hold the wire at one end and apply the torch to the other.  It won't take long before the copper becomes too hot to hold.

Exhausting Gasses Produced by the Cleaning Process

In many industrial cleaning processes it is necessary to exhaust emissions that unavoidably result from the cleaning process.  The reasons for exhaust can take on a large range -
  • Remove heat that would otherwise raise the temperature in the cleaning area
  • Remove humidity that would otherwise raise the humidity in the cleaning area
  • Remove toxic fumes that might otherwise be dangerous to workers
  • Remove mists of oil and other contaminants
  • Remove dust and other particles to prevent air contamination

How do you measure surface tension?

In the world of industrial cleaning technology we talk about surface tension a lot! So much so, in fact, that it is hard to enter into any discussion of cleaning without having the subject of surface tension arise.  In cleaning chemistry, for example, we are always looking for lower surface tension to promote penetration of small surface features and blind holes.  Surface tension has a major effect on ultrasonic cavitation and implosion.  A less well-known fact is that surface tension has a significant effect on the droplet size and pattern produced by spray nozzles.  So, if this thing called

Surface Tension and/or Wettability

A few days ago, I sat down to write what I thought would be a simple explanation of surface tension and how it is measured in the laboratory (a blog which will be published shortly if I can figure all of this out).  In doing the normal background research, however, I started to see contradictions that did not align with what I thought I knew about surface tension.  The culprit was wettability.  Soon I was in a circular argument with myself regarding the two and how to differentiate them. 

Ultrasonic Drying - Not Yet but Possible???

There has been a lot of buzz lately on the internet regarding work at the Oak Ridge National Laboratory to develop a dryer that uses ultrasonics instead of heat to dry things.  The major thrust seems to be to replace the conventional domestic clothes dryer (which uses heat to evaporate water) with one that uses ultrasonics to atomize instead of vaporize water to dry clothes.  Claims include drastically reduced energy consumption and shorter drying times.  As a result, there has also been some buzz about using the same idea (ultrasonics) to dry parts after ultrasonic cleaning.  The logic being

Venting

The environment in the area of an industrial cleaning system is often not a "healthy" one for personnel or equipment.  Caustic and acidic cleaning chemistries rise as mist above cleaning processes along with humidity and heat.  Although our first thought is to protect personnel from these hazards, the equipment can also suffer serious consequences as a result of long term exposure to the unfriendly and corrosive environment.  Although the problem is relatively easy to grasp, solutions are a bit more difficult and often prove to be more challenging than one might expect.