Spray Under Immersion – Like a Jacuzzi!

Liquid motion within and around a submerged part is one of many ways of enhancing both cleaning and rising processes.  In an earlier blog,

The BIG Four

agitation was described as one of the “big four” variables having a major impact on cleaning and rinsing.  In simple terms, agitation means moving the processing liquid relative to the part surface.  There are many ways to create agitation in a liquid processing system.  Probably the most common way is to simply agitate or move the parts being processed either up and down or from side to side.  This can be done manually or using simple automation consisting of an agitating platform in the tank or a suspending device above the tank which imparts vertical agitation.

In the above cases, motion of the part through the liquid creates the relative motion between the part and the liquid.  In cases where part agitation is not practical for one reason or another (weight, physical size, geometry, etc.), one option to enhancing cleaning or rinsing by providing agitation is a submerged spray.  This can be accomplished by simply pumping liquid from the tank and returning it through a submerged pipe, perforated tube or other device to provide relative motion between the part and the liquid.  Think of this very much like a Jacuzzi for parts cleaning.  Although effective when properly applied, this approach also has some serious limitations.

One major limitation is that the effect of a stream of liquid being introduced through a traditional nozzle rapidly diminishes as the distance from the source is increased.  Anyone who has had the opportunity to sit in a Jacuzzi bath (I’ve done hours of research this way) knows that you have to be pretty close to a nozzle to feel its effect.  In the center of the bath, there is liquid movement, but not much force.  In order to enhance the effect and perhaps make it more far-reaching, it is necessary to resort to either more pressure (larger pump, etc.) or the use of a special kind of nozzle called an “eductor.”  An eductor nozzle uses the venturi effect to increase the amount of liquid flow generated by a given rate of flow of liquid under pressure.

Illustration of an Eductor Nozzle

The first stage nozzle increases the velocity of the high pressure liquid being delivered. The resulting high velocity flow creates a low pressure area due to the Venturi effect which pulls additional liquid into the stream of flow.

Eductor nozzles, in general, increase the amount of liquid being moved, but they do not necessarily increase the velocity or effective “reach” of the effect.  The conservation of energy is preserved by the fact that the resulting overall flow if liquid has no more energy when it is returned through an eductor nozzle than it would have being returned through an open pipe or other conventional nozzle.  There is simply more liquid being moved but at a slower speed.

Eductor nozzles can be effective in increasing the amount of liquid movement but do not change the limitations of spray under immersion with regard to access to internal part surfaces and do not increase the force of the liquid stream delivered.  The only way to increase force is to move closer to a more conventional high velocity nozzle.

The next blog will discuss the effect of spray under immersion vs. agitation used in combination with ultrasonics to maximize cleaning and rinsing effects.


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