Entrainment foam, impact

Air may not immediately be thought of as a contaminant, but the presence of air in its various forms may have an impact on the ability of the lubricant to perform its design function. Almost all lubricating oil systems contain some air. Air is found in four phases free air, dissolved air, entrained air, and foam. Free air is trapped in a system, such as an air pocket in a hydraulic line, and may have minimal contact with the fluid. It can be a contributing factor to other air problems when lines are not bled properly during equipment startup and free air is drawn into circulating oils. 

Surface foam and entrained air can indeed be a serious hindrance to operations and quality in a paper miU. This can be a major economic problem recently it was estimated that the use of defoamers in the US paper industry alone in 2001 was over US 250 million and growing at over 5% annually. That is not the only cost of the problem - a much more significant impact to the papermaker would be the lost production and product quality problems that require the use of these products to control foam. 

Tissue In a mill manufacmring primarily facial grades from bisulfite pine and Kraft hardwood, the primary cause of foam is the wet strength resin used in production. The negative impact of foam is twofold. First, heavy foam would fill the basement, where the electrical room is located, creating the potential for a major fire. Second, entrained air in the stock would increase the workload on the fan pump, reducing machine efficiency and production. 

There is no substitute for hard work to survey the process systems and learn the pulp and papermaking process to understand potential incompatibilities and synergies with other wet-end additives and the process conditions, followed by laboratory studies evaluating different defoamer chemistries. Defoamers should be evaluated for their immediate effect to knock down surface foam and achieve longevity in performance, as well as impact entrained air. 

Nowadays, entrainment traps with string orifices are adopted. The vertical mesh orifice can be used as the section for final separation of liquid drops (Fig. 2.12, a), or to carry out preliminary separation and droplet coagulation (Fig. 2.12, b). In the latter case, the final separation of droplets is achieved in a horizontal mesh installed before the gas output branch pipe. In some gravitational gas-oil separators, the gas-liquid stream is directed toward a special reflector called a deflector (or baffle). The wall of the vertical separator can also act as a baffle. As a result of an impact of the liquid-gas mixture against the obstacle, the initial separation of gas from liquid occurs. To ensure smooth flow of liquid without foaming, separators are provided with a series of horizontal and inclined surfaces -shelves, cones, or hemispheres. 

It is well known that impact of inherent liquid drops can also cause air entrainment (see, e.g., reference [50]), a process that is in fact the basis of the well-known Ross-Miles pour test [51] (see Section 2.2.3). That drop impact can cause both the formation and destruction of foam would seem to be contradictory. It is, however, clearly a real effect that probably concerns the relative magnitude of variables such as the gas phase volume fraction in the foam, foam film thickness, and drop properties such as size, velocity, and frequency. Such a vague statement suggests the need for improved understanding of the phenomena associated with inherent liquid drop impact on foam and foam films. 

Features Provides foam control at significantly lower dose rates than many conventional water-based defoamers, without the negative impact of oil effective on both surface foam and entrained air RegiMory FDA 21 CFR 176.200,176.210... 

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