Mist traps

Mist traps limit the amount of the aerosols of mechanical pump oils from leaving the pump and drifting into the room containing the pump. These traps are different from the other traps in that they go on the exhaust of the mechanical pump and do not protect the pump or the system, only the operators. 

Mist traps trap oil aerosols (> 0.3 microns) from the exhaust port of mechanical pumps to minimize exposure to workers in the area. Since they cannot trap gases, vent tubes going to fume hoods are still recommended (see Fig. 7.14). 

Oxygen evolved from the anodes as well as some hydrogen from the cathodes produces a mist which is trapped by a froth maintained by adding cresyhc acid, sodium siUcate, and gum arabic, or glue plus cresol. Alkaline-earth carbonates prevent lead contamination of the cathode ziac. Most of the lead is deposited ia the cell sludge as iasoluble carbonate—sulfate. 

When oil buffered seals are used, oil will move past an inner seal toward the process side of the compressor. The oil is prevented from moving into the compressor by a set of labyrinths and is captured in an inner drain cavity. From the cavity, it is piped to the outside where it is collected in either a pot or trap. Figure 8-13 shows several alternative arrangements and equipment. The user must choose between automatic or manual drainers. If the gas from the top of the drainers is to be directly returned to the compressor, it is important that mist eliminators be used. The oil collected in the drainers is reclaimed or disposed of, based on the level of contamination and the user s disposal practices. 

In yet another incident a hydraulie hose leaked, and an oil mist was sueked into the air inlet of a diesel engine. It continued to run for three to five minutes after the normal fuel supply was isolated. The air filter on the engine was missing. Had it been present, it would probably have trapped the oil mist [23]. 

All the experiments were eondueted at the lowest volume veloeity of eompressed air that would generate a suitable mist. The volume veloeity was 5.7 liters per minute. The flow meter reading was 6 liters per minute. A horizontal glass trap 37.5 inehes long eonneeted the nebulizer with the interior of the ehamber. The internal diameter of the trap was approximately equal to that of the nebulizer output tube (approximately 5/8 internal diameter). The orifiee of the trap was flush with the inside wall of the ehamber. 

All exhaust from a mechanical pump should be vented to a fume hood regardless of the room s ventilation quality or the type of pumped gases. Each time you bring new samples into vacuum conditions, your system is pumping at atmospheric pressured Because pump oils have low vapor pressures, and pump oils themselves are considered nontoxic, there is little concern for breathing pump oil mist. However, there may be dangers from trapped vapors within the pump oils. Regardless, there is little reason to breathe the pump oil mist if it can be avoided. Check with the manufacturer or distributor of your pump for an oil mist filter for your pump. If you use a condensate trap, be sure you position your exhaust line so that material does not drain back into the pump (see Fig. 7.14). 

These traps do not significantly affect the flow rate, but without them, destructive wearing of the pump mechanism could result. Contact your pump supplier for filters to fit your specific pump. t This pumping tends to froth the oil, and the addition of an oil mist filter is imperative. 

Hatches Vents Characteristics Flame traps, reactions, exposures and solids Discharge, dispersion, radiation and mists Sludges, residues and fouling materials... 

The heat transfer mechanisms that are active in boiling in micro-channels can be summarized as follows (i) in bubbly flow, nucleate boiling and liquid convection would appear to be dominant, (ii) in slug flow, the thin film evaporation of the liquid film trapped between the bubble and the wall and convection to the liquid and vapor slugs between two successive bubbles are the most important heat transfer mechanisms, also in terms of their relative residence times, (iii) in annular flow, laminar or turbulent convective evaporation across the liquid film should be dominant, and (iv) in mist flow, vapor phase heat transfer with droplet impingement will be the primary mode of heat transfer. For those interested, a large number of two-phase videos for micro-channel flows from numerous laboratories can be seen in the e-book of Thome [22]. 

The deposition of fog droplets (diameter of a few pm) is sometimes separated from dry and wet deposition. In exposed sites of the higher altitudes of the mountain region (highlands), the precipitations within the forest stand may stem up to 50% from the trapping effect of cloud and fog droplets. Coniferous forests are efficient scavengers of mist and cloud droplets. Compared with rain water, in these deposits trace substances are accumulated (Schemenauer 1986, Kroll and Winkler 1988, Constantin 1993). Fog water contains nitrate- and sulfate-concentrations which are 10- to 100-fold larger than the concentrations in rain or snow. 

Small quantities of liquid should always be expected in column vapor outlets. The origin of this liquid can either be entrainment from the column (fine droplets can pass even through mist eliminators and coalesce in the overhead line), or atmospheric condensation. Low points in vapor outlet lines should be avoided as these tend to trap and accumulate liquid. The accumulated liquid back-pressures the column, causing instability, erratic operation, and slug flow into the downstream unit one case history where this occurred has been reported (203). Vapor outlet lines should be sloped (i.e., self-draining) ei-... 

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