Machinery Lubrication magazine published by Noria Corporation
Issue link: https://www.e-digitaleditions.com/i/1289708
AS I SEE IT e first sample is dry oil while the middle sample and the right sample have increasing amounts of emulsified water, hence the cloudy, turbid appearance. ere are two common ways emulsi- fied water can form in oil. e first is from colloidal condensation due to a supersaturated state of water in oil. is occurs when the oil's temperature drops below its dew point. e dissolved water concentration in oil is 100% when it is at its dew point. e colder the oil gets, the cloudier the oil becomes from condensation. e dew point temperature is influenced by the polar chemistry of both the oil's basestock and additives. e second way an emulsion can occur is from shear or mechanical agitation. In this case, free water is crushed by high mechanical mixing into the oil, similar to how mayon- naise is made in a blender. Crushing can occur by pumping, by fine filtration, from turbulent flow and at frictional zones (gears, bearings, etc.). Crushing can increase the interfacial (touching) surface area between the oil and the water by over one million times. is, combined with polar chemistry, locks the water in the oil, preventing it from stratifying downward easily. Typically, the size of micro-globules of water in oil is about 5-10 microns. Invert-Emulsion, the 4th State Above, I referred to water as being emul- sified in the form of micro-globules. In such case the oil is the continuous phase and the water globules are discontinuous (separated by oil). e 4th state relates to the inversion of water and oil as an emulsion. When an inversion happens, the water is in the contin- 4 | September - October 2020 | www . machinerylubrication.com Figure 1 Shown here is dry hydraulic fluid on the left and increasing amounts of emulsified water (water-in-oil) to the right. Figure 2. Illustrated example of the presence of the four states of water in oil. ere are so many determining factors that influence where the water is and how much water there is in each zone. uous phase and the oil is the discontinuous phase. e oil is the globule or micro-globule, not the water. e invert-emulsion typically occurs either at the interface between oil and free water or in the rare case when there is more water than there is oil in a turbulent vessel or circulating system. Many metal-working fluids and coolants are high-water based fluids, i.e., oil-in-water emulsions. e same is true for certain fire-resistant hydraulic fluids. Emulsified oil-in-water can easily be composed of 90% water or more. e high density of the water holds it down in sumps and reservoirs, meaning it is generally not as mobilized like its unruly sibling (water-in-oil). Figure 3 shows two oil samples that are clearly exhibiting evidence of all four states of water in oil. Figure 2 shows an annotated illus- tration of the common appearance and