Frost point

The eyeles in these power reeovery applieations are relatively simple. Figures 1-2 and 1-3 are typieal examples. The eyele eonfigura-tions involve the removal of solids or liquids ahead of the expander, and often the ineoming stream is heated so its temperature will not reaeh its frost point at the diseharge. This addition of heat also inereases the amount of available power. Some examples of this applieation are expansion of waste gas, waste produets of eombustion in oxidation proeesses, waste earbon dioxide, and expansion of high-pressure synthesis gas streams. 

The composition of the earth s atmosphere differs from day to day, from altitude to altitude, and from place to place. The largest variation is in the concentration of water vapor. Water evaporates continually from the hydrosphere, from the soil, from leaves, from clothes drying, etc. At intervals, parts of the atmosphere become chilled until the dew point or frost point is reached and then any vapor in excess of the saturation amount is precipitated as rain or snow. 

At any rate, these PSCs, which can be either liquid or solid, are known as Type I PSCs and form at temperatures about 2-5 K above the ice frost point. They are believed to contain large amounts of nitric acid and water (Fahey et al., 1989 Pueschel etal., 1989,... 

As the temperature falls below the ice frost point, water condenses out as ice, forming large particles (Fig. 12.21). These are known as Type II PSCs. They are formed at lower temperatures corresponding to the frost point of water ( 188 K for stratospheric conditions), or possibly 2-3 K below that (Tabazadeh et al., 1997). They are much larger than Type I PSCs, of the order of 5-50 jum in diameter, and consist mainly of... 

LIDAR measurements of stratospheric aerosols (Browell et al., 1990) show that above the frost point, PSCs can be solids, perhaps solid SAT. Pure SAT, which does not form PSCs very efficiently, does not melt until quite high temperatures, about 210-215 K (Middlebrook et al., 1993 Iraci et al., 1995). However,... 

However, at lower HNO, concentrations than assumed, e.g., in a denitrified atmosphere, the formation of the liquid is shifted to temperatures about 3 K lower than shown in Fig. 12.22 (Martin et al., 1998). In addition, Martin et al. (1998) predict that under these conditions, SAT will not deliquesce to a liquid solution at temperatures above the frost point as shown in Fig. 12.22. Their experiments also suggest that the formation of the liquid, although thermodynamically favored, may be too slow to be important under stratospheric conditions. 

This reactive nitrogen may then be actually removed from the air parcel when the particles containing it grow large enough, at least several micrometers in diameter, to gravitationally settle out in less than a day (26). The mechanisms for this particle growth are not completely understood, but one possibility is that water vapor condenses on the nitric acid-water core as the temperature decreases below the frost point. These particles then be-... 

DEW POINT. The temperature to which a given parcel of air must be cooled at constant pressure and constant watervapnr content in order for saturation to occur, ihc temperature at which the saturation vapor pressure of the parcel is equal tu the actual vapor pressure of ihc contained water vapor. Any further cooling usually results in the formation of dew or frost. Also called dewpoint temperature. When this temperature is below 0 C.. it is sometimes called the frost point. 

Therefore, the partial pressure of water v tiptir in air is directly related Io the measurement of humidity This vapor pressure varies horn 1.22 x 10 mb imillihan of mercury (0.122 Pascal) at the -7 C frost point of "hone dry" arctic or industrial dry air—to 1.013 x I01 mb ol mercury 10.1013 x IO1 Pasculi at ihe IIX) C dew poini of saturated hot air in a product drier This is a change of almost a million to one over the span of interest in industrial humidity measurement,... 

FISH (Fast In-situ Stratospheric Hygrometer) is a stratospheric hygrometer based on the Lyman-alpha photofragment fluorescence technique. The instrument performs measurements of the stratospheric water vapour content (total water and gas phase) in the range 500 - 0.2 ppmv (precision < 4 %, accuracy 0.2 ppmv) with a time resolution of 1 s. The instrument is calibrated in the laboratory against a frost point hygrometer at real stratospheric conditions. 

Figure J. Possible pathways for stratospheric aerosol formation Left path the conventional 3-stage model ( SAT, NAT, [ice) the aerosol remains solid. Right path the aerosols remains liquid, takes up HNOj forming ternary supercooled solution, and freezes out below the frost point [15,28].

Nitrogen is used to blanket the reaction and the raw materials to stop the absorption of moisture and to prevent oxidation of the product. The dew point of a gas is the temperature at which the water vapor present in the gas saturates the gas and begins to condense. Dew points of below 0°C are sometimes called the hoar-frost point. Industrial-grade nitrogen gas normally is dry enough for use. 

Aviator s breathing grade oxygen, used because of its low moisture content, was delivered to the ozonator through a pressure regulator, an iron case meter, and an orifice manometer. Suitable connections were provided for measuring the frost point, pressure, and temperature. 

P. Pressure T. Temperature W. Water S. Sample P.P. Frost point... 

In this experiment, where hydrogen was admixed with the oxygen, the amount of water produced in the ozonator was determined by the frost point method. The difference between inlet and outlet moisture content was taken as the amoimt produced by the reaction. Only about 4% of the hydrogen added was converted to water. The reduction in energy yield of ozone generation was greater than would be produced by this amount of water added as such. 

It is concluded that for optimum ozonator operation, the oxygen feed should be dried to a frost point of at least —60° C., and that introduction of water to the oxygen should be avoided in all cases. 

Oltmans, S.J., H. Vohnel, D.J. Hofmann, K. Rosenlof, and D. Kley, The increase in stratospheric water vapor from balloon-borne frost point hygrometer measurements at Washington, DC and Boulder, Colorado. Geophys Res Lett 27, 3453, 2000. 

Partly because of limited analysis of Antarctic stratospheric temperatures, early studies that followed the discovery of the ozone hole were not specific about the type of particles of which the observed PSCs were composed. It was generally assumed that the particles were mainly water ice (Steele et al., 1983). Stratospheric ice clouds are frequently optically thick and brilliant in color. Such clouds form when temperatures drop below the temperature at which ice forms (frost point), and are now referred to as Type 2 PSCs. However, sensitive satellite measurements (McCormick et al, 1982) suggested that optically thinner PSCs were also present at warmer temperatures. 

Polar stratospheric clouds have been classified into two broad types, so-called Type I and Type II (Table 4.1). Type I PSCs have been further subdivided into Type la and Type Ib. Type la PSCs have traditionally been identified as crystals of nitric acid trihydrate, HNO, 3 H2O, denoted NAT, that form once temperatures fall below about 195 K. Type lb PSCs consist of supercooled ternary solutions of HNO3/H2SO4/H2O, also forming at about the same temperature threshold. Type II PSCs are largely frozen water ice, nonspherical crystalline particles, that form at temperatures below the ice frost point. The ice frost point, for example, at 3 X 10 Torr H O is 191 K. Despite the above classification, the composition of PSCs is still uncertain (Toon and Tolbert, 1995). 

It has been pointed out recently, that the question of homogenous and heterogeneous freezing of stratospheric aerosols is one of the key questions in the understanding of the physico-chemical behavior of the PSCs. According to the phase diagram of liquid sulfuric acid solutions, PSCs were initially believed to consist solely of solid particles, while it now seems clear from experimental observations and theoretical considerations that most of the PSCs stay liquid above the ice frost point.It is still not clear, however, why sometimes solid PSCs are found above the ice frost point, and how they are formed. 

Dew/frost-point hygrometer Thermometer Measures water in gases range 10" -90% water... 

Dew/frost-point hygrometer - utilizing a chilled mirror surface. The mirror is maintained at the dew-point temperature by automatically controlling the current through a thermoelectric cooler. A 100-Q platinum resistance thermometer is... 

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