- Entrained air in coolant fluids
Entrained Air/Dissolved Air(Foam) in Coolants & other fluids
Entrained and dissolved air that are present in coolants (machine tool industry), oils (cutting tools & hydraulics) andsolutions used in paper/pulp industries can cause various kinds of problems, including:a. Reduction of pump efficiency(cavitation) b. Bacterial growth c. Dirt flotation d. Reduced effectiveness of the fluid solution(s)f. Eventual downtime to clean tankse. Defoamer useg. Cost of replenishing the oil or solutionh. Cost of entire material rejection due to imperfections
The three main classes of air that are of concern to the mechanical systems area. Dissolved air; (Dissolved air behaves as part of the water phase, except that it can come out of solution as small bubbles (entrained air)b. Entrained air; (Entrained air consists of bubbles that are small enough to collect on top of a fluid.)c. Bubbles; (Bubbles that have sufficient buoyancy to rise to the surface and are described as foam.)
Although chemical factors can contribute to foam, it is important to consider mechanical factors that can contribute to airproblems:a. Leaky seals on pumpsb. High pressure pumpsc. Poor tank, pump inlet, outlet and manifold design
A most common solution to entrained air (foam) problems is to employ a defoamer product. A wide variety of chemicalformulas are available to promote coalescence of foam. An essential feature of a defoamer product is a low viscosity anda facility to spread rapidly on foamy surfaces.
An additional factor, often overlooked, with dissolved and entrained air, is that a problem can be expected if the coolant isexposed to acidic conditions below a pH value of 6.5 in that a reaction between certain chemical additives and a pH valuebelow 6.5 can lead to the release of carbon dioxide gas. The high solubility of CO2 means that a larger portion of this gaswill tend to remain dissolved in the water.Consequently, even when foam (bubbles) are gone from the surface, it is quite possible entrained/dissolved airwill remain, in the fluid and, eventually, cycle out as more foam (bubbles).
Conclusion, it is extremely important that the percent of entrained air, in any fluid, especially fluid in conjunction with a coolant filtration systems, hydraulic system oils and paper/pulp solutions, all systems that are associated with many high pressure pumps, and utilizing defoamer to control foam, be measured and determined, efficiently and accurately, on a daily basis, with a standard microprocessor, dial reading, entrained air measuring device,rather than the inaccurate laboratory procedure now employed.
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