Atmospheric condensation

If condensation requires gas stream cooling of more than 40—50°C, the rate of heat transfer may appreciably exceed the rate of mass transfer and a condensate fog may form. Fog seldom occurs in direct-contact condensers because of the close proximity of the bulk of the gas to the cold-Hquid droplets. When fog formation is unavoidable, it may be removed with a high efficiency mist collector designed for 0.5—5-p.m droplets. Collectors using Brownian diffusion are usually quite economical. If atmospheric condensation and a visible plume are to be avoided, the condenser must cool the gas sufftciendy to preclude further condensation in the atmosphere. 

Water contamination is a constant threat. The sources of water are many—atmospheric condensation, steam leaks, oil coolers, and reservoir leaks. Rusting of machine parts and the effects of rust particles in the oil system are the major results of water in oil. In addition, water forms an emulsion and, combined with other impurities, such as wear metal and rust particles, acts as a catalyst to promote oil oxidation. 

Water contamination in the oil system can cause serious damage to turbomachinery, and every reasonable effort should be made to, first, prevent its entrance into the system, and second, provide suitable removal equipment if water cannot be effectively kept out. Experience indicates that designers and equipment operators can be more effective in keeping water out of the system. Since the main sources of contamination are atmospheric condensation, steam leaks, and faulty oil coolers, preventive measures should be taken. 

When steam pressures in the chest are near atmospheric, condensate can rise in the shell and drastically reduce avail-ahle surface—if the trap is too small to dump steam into the condensate return system or if the condensate return pressure is greater than the calculated chest pressure required. In these cases, the steam pressure will have to rise in the chest to overcome this error, if steam pressure is available. If not, the rehoiler will not deliver design flux. 

Condensate normally contains no hardness and is very low in dissolved solids. Unless it has been excessively exposed to the atmosphere, condensate is also very low in dissolved oxygen. Therefore it represents the ideal feedwater, and the higher the proportion of recovered condensate in the feed, the easier it will be to maintain the boiler water within the desired limits. The percentage condensate return is thus basic to all considerations of water management for the boiler circuit. 

The atmospheric condenser is a simplified form of evaporative condenser, having plain tubes over a collecting tank and relying only on natural air draught. This will be located on an open roof or large open space to ensure a good flow of air. The space required is of the order of 0.2 m /kW, and such condensers are not much used because of this large space requirement. Atmospheric condensers can still be seen on the roofs of old breweries. They are in current use where space is plentiful. 

Since 1995, the sparks solvent/fuel site located in Sparks, Nevada, a remediation system consisting of MPE, air sparging, and SVE, has been operational. The treatment system consists of 29 MPE wells, an oil-water separator, and a fluidized bed bioreactor, with an influent flow rate of 23.3 L/s (370 gpm) and a retention time of 8 min. Vapors are sent through a condenser, followed by a thermal oxidizer, before its release to the atmosphere. Condensate is sent back through the oil-water separator. Performance data, available for the first 650 days of site operation, showed a reduction in MTBE concentration across the bioreactor from 2400 to 55 pg/L. No data were provided for reduction of MTBE concentrations in the aquifer.51... 

The nature and behavior of free Rn-d ions or atoms, i.e. not attached to atmospheric condensation nuclei, is still subject of controversy, particularly with regard to the influence of environmental atmospheric conditions, such as humidity and presence of other gases (Busigin et al., 1981). Free Rn-d atoms are one of the most critical parameters for the exposure-dose conversion. This can be of particular importance in indoor exposure situations with a large ratio of unattached to attached Rn-d. 

Hounam, R. F. The deposition of atmospheric condensation nuclei in the nasopharyngeal region of the human respiratory tract. Health Phys. 20 219-220, 1971. (letter)... 

Water contamination of fuel occurs. Water can originate from fuel processing, atmospheric condensation, or external sources. Water may contain dissolved salts, may be acidic or basic, or may contain solubilized organic compounds. Water-initiated corrosion can result. 

This has important implications for nucleation in the atmosphere. Condensation of a vapor such as water to form a liquid starts when a small number of water molecules form a cluster upon which other gaseous molecules can condense. However, the size of this initial cluster is very small, and from the Kelvin equation, the vapor pressure over the cluster would be so large that it would essentially immediately evaporate at the relatively small supersaturations found in the atmosphere, up to 2% (Prup-pacher and Klett, 1997). As a result, clouds and fogs would not form unless there was a preexisting particle upon which the water could initially condense. Such particles are known as cloud condensation nuclei, or CCN. 

The flash gas from the top of F-l passed through a wet-test meter to a sample tap and was vented to the atmosphere. Condensed liquid product was collected through a valve at the bottom of F-7, weighed, and analyzed. 

In the direct route, water molecules in the ocean evaporate into the atmosphere, condense to form clouds, and then precipitate into the ocean as either rain or snow, to begin the cycle anew. 

About 3800 million years ago, when the Earth had cooled below 100 °C, the water vapour in this atmosphere condensed and fell as rain. This caused the formation of the first oceans, lakes and seas on the now rapidly cooling Earth. Eventually, early forms of life developed in these oceans, lakes and seas at depths which prevented potentially harmful ultraviolet light from the Sun affecting them. 

A hydrophilic sphere of radius Rp = 5 /xm sits on a hydrophilic planar surface. Water from the surrounding atmosphere condenses into the gap. What is the circumference of the meniscus Make a plot of radius of circumference x versus humidity. At equilibrium the humidity is equal to P0K/-Po-... 

A bit of explanation is required here for those readers unfamiliar with the condensation concept, a key notion to describe polyelectrolytes. Consider as here a polyanion. If the charges are brought closer to one another, on the average, below a critical distance their mutual repulsion is such that — in order to continue to obey first principles electrostatics such as the Poisson equation — they screen themselves with an atmosphere of counterions. This atmospheric condensation, which can coexist with ionic binding at the individual sites, boosts the local concentration of counterions in the space surrounding the polyelectrolyte by as much as three orders of magnitude. The nmr measurements analyzed here focus on these water hydration molecules coordinated to condensed sodium counterions, next to the surface of the tactoids (see Fripiat s chapter). 

When the plant is located in built-up areas, there might also be an atmospheric condenser that receives the steam, which is vented during the startup to decrease the noise level at the plant. The auxiliary circuits of the steam turbine are the lube oil, control fluid, and vacuum system for the condenser. 

The determination of the mass and size of atmospheric condensation nuclei. Trans. Faraday Soc., 32 (Part 8) 1175-1179. 

Several areas in which chemical measurement technologies have become available and/or refined for airborne applications have been reviewed in this paper. It is a selective review and many important meteorological and cloud physics measurement capabilities of relevance to atmospheric chemistry and acid deposition (e.g., measurement of cloud liquid water content) have been ignored. In particular, we have not discussed particle size spectra measurements for various atmospheric condensed phases (aerosols, cloud droplets and precipitation). Further improvements in chemical measurement technologies can be anticipated especially in the areas of free radicals, oxidants, organics, and S02 and N02 at very low levels. Nevertheless, major incremental improvements in the understanding of acid deposition processes can be anticipated from the continuing airborne application of the techniques described in this review. 

Internal vessel heating and agitation add cost, but these capabilities are required to ensure uniform and efBcient contaminant removal. In addition, internal heating is required during pressure letdown to prevent atmospheric condensation on the parts when the vessel is opened. The parts may be below room temperature due to the cooling effect caused by the expansion of the carbon dioxide during depressurization. This is especially important if the cleaning is not performed in climate controlled atmospheres. 

By acting as condensation nuclei. It is well documented (e.g. Twomey. 1971) that atmospheric condensation nuclei consist mainly of ammonium sulfate. 

McWilliams, S., 1969 The concentration of atmospheric condensation nuclei at Valentia observatory. Irish Meteorological Service, Techn. Note No. 33, Dublin. 

Atmospheric chemistry is dominated by trace species, ranging in mixing ratios (mole fractions) from a few parts per million, for methane in the troposphere and ozone in the stratosphere, to hundredths of parts per trillion, or less, for highly reactive species such as the hydroxyl radical. It is also surprising that atmospheric condensed-phase material plays very important roles in atmospheric chemistry, since there is relatively so little of it. Atmospheric condensed-phase volume to gas-phase volume ratios range from about 3 x KT7 for tropospheric clouds to 3 x ICE14 for background stratospheric sulfate aerosol. 

Bashurova, V. S. et al. (1992) Measurements of atmospheric condensation nuclei size distributions in Siberia, J. Aerosol Sci. 23, 191-199. 

The presence of ions has been shown experimentally to enhance the rate of nucleation of liquid drops in a supersaturated vapor. Katz et al. (1994) showed, for example, that the nucleation rate of n-nonane, measured in an upward thermal diffusion cloud chamber, at an ion density of 16 x 106 ions cm-3, increased by a factor of 2500 over that in the absence of ions. These investigators also confirmed experimentally that the nucleation rate is directly proportional to the ion density. The phenomenon of ion-induced nucleation plays an important role in atmospheric condensation, particularly in the ionosphere. While both positive and negative ions increase the nucleation rate, many substances exhibit a preference for ions of one sign over the other. 

The stability and maintenance of a cleaned surface is often more critical than the final surface state which is achieved after the cleaning process. Storage in an ultraclean, controlled environment, a very expensive but most effective measure is usually seldom required. Instead of using a universal protection device, it is often easier and cheaper to identify the undesirable contaminants and to eliminate them from the storage environment. Such contaminants are usually the airborne ones, including various types of dust particles, atmospheric condensates of chemical vapours, and, last but not least, water vapour. The use of some preventive measures is, therefore, well worth considering. Contact with dust may be reduced drastically by storing the parts in a closed container or in a clean bench. 

Traces of heavy metals in waters are of industrial origin (waste waters from mining and treatment of ores, from metallurgical plants and rolling mills, metal finishing, photographic shops, from textile, leather, and chemical industry, and even from agriculture (e.g. cadmium from African phosphate fertilizers ). An additional source are atmospheric condensations contaminated by exhalations from combustion of fossile fuels and from motor vehicles. 

An atmospheric condenser may be required beyond the vacuum pump. 

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