Characteristic temperature Cloud

Recent space-probe and earth-based spectroscopic studies of the planet Venus suggest how much remains to be learned about the other planets. Earlier estimates of the surface temperature of Venus placed it near 60°C. The more detailed studies show, however, that two characteristic temperatures can be identified, —40°C and 430°C. The lower temperature is attributed to light emitted front high altitude cloud tops. The higher temperature is likely to be the average surface temperature. 

On a global scale, the atmosphere serves as the major pathway for the transport and deposition of contaminants from emission sources to terrestrial and aquatic ecosystem receptors (22, 27). Once a contaminant is airborne, the processes of atmospheric di sion, transport, transformation, and deposition act to determine its fate. These processes are complex and the degree to which they influence the fate of a particular contaminant is dependent on its physico-chemical characteristics, the properties and concentrations of coexisting substances, and the prevailing meteorological conditions, including wind, precipitation, humidity, temperature, clouds, fog, and solar irradiation. 

Surfactant blends of interest will exhibit clouding phenomena in aqueous solutions undergoing a phase transition from a one phase system to a two phase system at a discrete and characteristic temperature, referred to as the Cloud Point (CP). This value indicates the temperature at which sufficient dehydration of the oxyethylene portion of the surfactant molecule has occurred and this results in its "displacement" from solution. The addition of lyotropic salts will depress the CP, presumably due to the promotion of localised ordering of water molecules near the hydrophilic sheath of the surfactant molecule (8). Furthermore, the addition of different oils to surfactant solutions can induce either an elevation or a depression of the recorded CP and can be used to qualitatively predict the PIT (8x9). 

In temperate climates, diesel fuel must remain fluid at temperatures below the minimum expected temperature for the season. Through much of North America, winter diesel fuels have low temperature flow points below —30°C. Diesel fuels with low pour points have lower viscosity and often lack lubricity (110). These fuels typically provide little lubricity. For example, Noureddini (111) reports that biodiesel fuels that are simple esters of various vegetable oils have poor flow characteristics below a temperature of —2°C. To overcome this difficulty, a solvent consisting of mixed ethers of glycerol is added to the biodiesel. The resultant fluid has a low temperature cloud point below —32°F (—36°C). The pour point of this fluid is still above that necessary to effectively add to many winter diesels, as it may be necessary to pour the fuel component at temperatures as low as —45°C. 

If aqueous solutions of many nonionic surfactants are heated, they become turbid at a characteristic temperature called the cloud point (see Fig. 6.31 in section 6.4). Other nonionic surfactants have cloud points above 100 C. The process is reversible, that is, cooling the solution restores clarity. The turbidity at the cloud point is due to separation of the solution into two phases. At temperatures up to the cloud point an increase in... 

Many of the physical characteristics of the atmosphere, such as wind, temperature, cloud cover, humidity, and precipitation, are easily perceived. Sometimes, chemicals in the atmosphere also can be observed, as in smoke plumes and smog, and their physical transport tracked downwind just as downstream transport of substances in a river can be measured. Other atmospheric processes are less apparent to the unaided observer, however, occurring either on the microscopic scale of a chemical reaction, or on a global scale, or at high altitudes. Such processes may be detected only by instrumentation on satellites or some high-altitude aircraft. 

The Krafft temperature of ionic surfactants varies as a function of both the nature of the hydrophobic group and the ionic character of the head group. Nonionic surfactants, because of their different mechanism of solubilization, do not exhibit a Krafft temperature. They may, however, have a characteristic temperature-solubihty relationship in water in that they may become less soluble as the temperature increases. In some cases, phase separation is found to occur, producing a cloudy suspension of surfactant aggregates. The temperature at which that occurs is referred to as the cloud point. ... 

At lower temperatures, the crystals increase in size, and form networks that trap the liquid and hinder its ability to flow. The pour point is attained which can, depending on the diesel fuel, vary between -15 and -30°C. This characteristic (NF T 60-105) is determined, like the cloud point, with a very rudimentary device (maintaining a test tube in the horizontal position without apparent movement of the diesel fuel inside). 

In the dense interstellar medium characteristic of sites of star fonuation, for example, scattering of visible/UV light by sub-micron-sized dust grains makes molecular clouds optically opaque and lowers their internal temperature to only a few tens of Kelvin. The thenual radiation from such objects therefore peaks in the FIR and only becomes optically thin at even longer wavelengths. Rotational motions of small molecules and rovibrational transitions of larger species and clusters thus provide, in many cases, the only or the most powerfiil probes of the dense, cold gas and dust of the interstellar medium. 

Propylene is a colorless gas under normal conditions, has anesthetic properties at high concentrations, and can cause asphyxiation. It does not irritate the eyes and its odor is characteristic of olefins. Propjiene is a flammable gas under normal atmospheric conditions. Vapor-cloud formation from Hquid or vapor leaks is the main ha2ard that can lead to explosion. The autoignition temperature is 731 K in air and 696 K in oxygen (80). Evaporation of Hquid propylene can cause skin bums. Propylene also reacts vigorously with oxidising materials. Under unusual conditions, eg, 96.8 MPa (995 atm) and 600 K, it explodes. It reacts violentiy with NO2, N2O4, and N2O (81). Explosions have been reported when Hquid propylene contacts water at 315—348 K (82). Table 8 shows the ratio TJTp where is the initial water temperature, and T is the superheat limit temperature of the hydrocarbon. 

Volume of vessel (free volume V) Shape of vessel (area and aspect ratio) Type of dust cloud distribution (ISO method/pneumatic-loading method) Dust explosihility characteristics Maximum explosion overpressure P ax Maximum explosion constant K ax Minimum ignition temperature MIT Type of explosion suppressant and its suppression efficiency Type of HRD suppressors number and free volume of HRD suppressors and the outlet diameter and valve opening time Suppressant charge and propelling agent pressure Fittings elbow and/or stub pipe and type of nozzle Type of explosion detector(s) dynamic or threshold pressure, UV or IR radiation, effective system activation overpressure Hardware deployment location of HRD suppressor(s) on vessel... 

Cloud Point Measurements Cloud points were recorded by the visual observation of aqueous solutions containing 1% W/V surfactant. The measurement defines the temperature at which the system under test shows a characteristic transitional change from a clear solution to an opalescent or cloudy state. All cloud points were recorded in both ascending and descending temperature cycles to ensure data confidence. The influence of salt and/or oils on the cloud point were systematically evaluated. 

This cloud of fog is due to a significant drop in temperature in the headspace below the champagne surface, caused by the sudden gas expansion when the bottle is uncorked. Actually, this sudden temperature drop is responsible for the instantaneous condensation of water vapor into the form of this characteristic cloud of fog. Assuming an adiabatic expansion experienced by the gas volume of the headspace (from about 5 to 1 atm), the corresponding theoretical drop in temperature experienced by the gas volume may easily be accessed by the following and well-known relationship ... 

The cloud point test is one of the most commonly used methods to evaluate the low-temperature characteristics of distillate fuel. The cloud point temperature identifies the point when wax begins to form into crystals large enough to become visible in the fuel. At this temperature, wax can settle from fuel, deposit onto fuel filters, and interfere with the flow of fuel through small tubes and pipes. During cold weather months, distillate fuels with lower cloud point values are refined and blended to minimize the low-temperature problems associated with wax. 

Tlhis paper describes the physical and radiochemical characteristics of selected debris from the Kiwi Transient Nuclear Test (TNT) (6, 7). This transient test was conducted in Nevada by the Los Alamos Scientific Laboratory (LASL), and produced approximately 3 X 1020 fissions (1). Zero time was 1059 PST on 12 January 1965. About 5% of the reactor core was vaporized, and some 68% was converted to a cloud of particulate. The measured maximum temperature was 4250°K. (7). Large pieces of fuel rods were recovered near ground zero. 

A large body of work has been developed by DeSimone and co-workers on the solubility of fluorinated polymers, especially polyfl,l-dihydroper-fluorooctylacrylate) fPFOA), in C02 (Hsiao et al., 1995 Luna-Barcenas et al., 1998). An excellent example of utilizing creative chemistry to design a C02-soluble polymer, PFOA is one of the very few fluoropolymers that dissolves in C02 at modest temperatures and pressures less than 300 bar. The characteristics needed to make a fluoropolymer soluble in C02 can be ascertained from Figure 7.2, which shows the difference in cloud-point curves for polyfvinylidene fluoride) (PDVF), a statistically random copoly-... 

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