Entrained air in coolants

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Entrained Air (foam) in Coolant Filtration Systems Definitions, Causes, Problems and Solutions

The most general definition of entrained air (foam) is a substance that is formed by trapping many gas bubbles in a liquid. Entrained air (foam) can mean a “bubbly liquid” as in a soap solution but it is also produced as an often un-wanted by-product in manufacturing processes. Entrained air (foam) can be a serious problem, in chemical and biochemical solutions, especially when these solutions are agitated over long periods of time, without enough settling time to allow the bubbles to surface and break up.

Air( dissolved oxygen) can be found in any water based coolant or filtration system in several different forms including: A. Entrained air (small bubbles-foam) B. Air pockets (both free moving and trapped by tank and piping design of the system) C. Absorbed (dissolved air) (found in all non-purified water).

Entrained air (foam) and air pockets can be seen by the naked eye however, absorbed (dissolved) air is not visible to the naked eye. In some instances, tap water may contain as much as 3-8% dissolved air. Production problems caused by entrained air (foam) are: Reduction of pump efficiency Reduced effectiveness of the coolant solution Bacterial growth Administering of defoamers Dirt flotation Eventual downtime to clean tanks and change coolant

Entrained air (foam) situations, causing pump cavitation and coolant problems, can happen quite often post process installation as a result of inadequate engineering at conception or just as common, changing of conditions during component selection, consequently, no single fault or responsibility can be directly identified as the culprit, due to the influences of each discipline upon the other.

Pump installation layout, centerline dimensions, distance to obstructions, etc, are all well published and acknowledged guidelines and procedures and this may not be the root issue, because many times, the core culprit of a performance deficiency, is not that simple.

Coolant selection, in conjunction with water purity and other additives, can contribute to foam and as does coolant high-pressure delivery systems to work heads and, moreover, normally, coolant technicians, plant operational personnel and coolant management companies, unless instructed to do so, seldom perform routine testing of coolant for entrained air, from the various locations – tanks, nozzles, flumes, pumps and make up water.

The point is, if the entrained air values, on site, are in excess of the pump manufacturers limitations and coolant companies specifications, the entrained air problem must be recognized, by testing and corrected. It can not be allowed to continue to be treated solely by defoamers.

When pump and entrained air deficiencies are both present in a filtration system, the effect of one deficiency dramatically influences the degree of the other consequently, both become difficult to solve and to solve, cooperation between all disciplines, must be quite pragmatic. If this cooperation is not evident, there will be no progress.

Each of the disciplines involved will share responsibility for determination, identification and elimination of these coolant filtration process problems:

1. Verify all pump engineering details are correct within the filtration system specifications.

2. Verify, by using a Quick air test device, the entrained air volume, in the coolant solution, is under the maximum percent allowed by pump and coolant suppliers.

3. Verify the coolant and water choice are not different than originally planned and the entire system is not grossly contaminated.

4. Verify that tramp oil is not excessive and may or may not be a contributing entrained air factor because tramp oil or similar contaminants can weaken surface tension and the lack of surface tension can trap bubbles, eventually, creating foam.

5. Verify, at many different downstream and upstream locations, the percent of entrained air existing in the coolant.

6. If using a media filter to filter, ascertain small or large entrained air bubbles are not plugging the media as such a circumstance is quite prevalent with the presence of foam and will contribute to poor filtration.

7. A consequence of not ascertaining the presence of air bubbles (foam) is usually the recommendation to use defoamers and, not only that use may not be necessary but when used, will definitely increase manufacturing costs, beyond reasonable limits.

8. Even if all mechanical factors are verified good but entrained air (foam) remains in the coolant, it is still an identifiable culprit of overall performance issues and must be corrected.

9. Whatever is imparting and retaining the entrained air must be determined and eliminated in order that the system function properly and all other issues rendered moot.

10. All the issues could be/should be addressed and resolved consequently, the major solution, to a "real" coolant filtration solution or process component limitation, is the spirit of cooperation between responsible groups and this cooperation is essential and must be forthcoming from all parties before any problem can be solved.