Cooling Fogging

I think one will develop cold fog — super-cool fog which of course in itself may mean an enormous hazard to vegetation. This is a hting we have not discussed so far, but that could be extremely hazardous for land vegetation. 

Fog and stratus are clouds, but the base of fog rests on the Earth s surface and stratus clouds are above the surface. Although the substance of fog and cloud is the same, their processes of formation are different. Clouds form mainly because air rises, expands, and cools. Fog results from the cooling of air that remains at the Earth s surface. Scientists at the University of Nevada recently revealed the following characteristics for convection over oceans when warm air flows over cooler water, the air layer over the sea will usually convect even when the water surface... 

The mechanism of this spring fog is different from typical spring and summer fog. The spring and summer fog is almost advection cooling fog in previous research, while in this spring fog, the intersection of south and north winds over Yellow Sea increased the relative humidity, and then formed the mixing fog at first. And then after May 9, it slowly turned into evaporation advection fog due to the decrease of air temperature. 

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. 

Cooling-Tower Plumes. An important consideration in the acceptabiHty of either a mechanical-draft or a natural-draft tower cooling system is the effect on the environment. The plume emitted by a cooling tower is seen by the surrounding community and can lead to trouble if it is a source of severe ground fog under some atmospheric conditions. The natural-draft tower is much less likely to produce fogging than is the mechanical-draft tower. Nonetheless, it is desirable to devise techniques for predicting plume trajectory and attenuation. 

Not only may the cooling-tower plume be a source of fog, which in some weather conditions can ice roadways, but the plume also carries salts from the cooling water itself. These salts may come from salinity in the water, or may be added by the cooling-tower operator to prevent corrosion and biological attack in the column. 

Although the dew-point method may be considered a fundamental technique for determining humidity several uncertainties occur in its use. It is not always possible to measure precisely the temperature of the polished surface or to eliminate gradients across the surface. It is also difficult to detect the appearance or disappearance of fog the usual practice is to take the dew point as the average of the temperatures when fog first appears on cooling and disappears on heating. 

Evaporative methods-direct water fogging Refrigerated inlet cooling systems-ical refrigeration... 

Direct inlet fogging, is a type of evaporative cooling method, where de-mineralized water is converted into a fog by means of high-pressure nozzles operating at 1000-3000 psi. (67-200 Bar) This fog then provides cooling... 

Condensation occurs when air temperatures cool. The cooling occurs in one of two ways. Either the air vapor cools as it rises and expands or as it comes into contact with a cool object such as a cold landmass or an ice-covered area. Air rises for several reasons. It can be forced up as it encounters a cooler, denser body of air, or when it meets mountains or other raised land masses. It can rise as it meets a very warm surface, like a desert, and become more buoyant than the surrounding air. Air also can be forced to rise by storms—during tornadoes particles of air circling to the center of a cyclone collide and are forced up. When the water vapor collides with a cold object, it can become fog, dew, or frost as it condenses. The vapor cools as it rises into the atmosphere and condenses to form clouds and, sometimes, rain. 

The running of a cool airflow under a warm wind is another cause of temperature inversion. As a rule, the presence of an inversion implies a highly stable atmosphere one in which vertical air movements is rapidly damped out. In such a situation, fog and airborne pollutants collect, being unable to move freely or be dissipated by convection. 

M14. Moeck, E. O., Dryout in a 19-rod bundle cooled by steam/water fog at 515 psia, ASME Paper 65-HT-50 (1965). 

The formation of dew and fog are consequences of this variation in relative humidity. Warm air at high relative humidity may cool below the temperature at which its partial pressure of H2O equals the vapor pressure. When air temperature falls below this temperature, called the dew point, some H2 O must condense from the atmosphere. Example shows how to work with vapor pressure variations with temperature, and our Chemistry and the Environment Box explores how variations in other trace gases affect climate. 

Fog forms when humid warm air from above a body of water moves inland and cools. What is the highest temperature at which fog could form from air that is at 65% relative humidity when its temperature is 27.5 ... 

Cloud Chambers A chamber containing air saturated with vapor is used. Radioactive particles ionize air molecules in the chamber. Cooling the chamber causes droplets of liquid to condense on these ions, giving observable fog-like tracks. 

Evaporative Technologies These TIC technologies cool the inlet air by vaporizing water in direct contact with the inlet air, using the latent heat of vaporization of water. These technologies either spray water directly into the airstream as a fog or mist or evaporate the water from fixed wetted media placed in the airstream. 

Give 0.2 ml of cone, sulfuric acid to 1 - 2 ml of aqueous sample. Concentrate the liquid carefully in a hood at about 130 °C and then heat to 280 °C until white fog appears. After cooling, add one to two drops of cone, nitric add and heat again until nitrous gases are visible. After cooling, add 2 ml of Soln. D, boil the solution for a short period, and fill up to 5.0 ml with ddH20. 

Nitrous acid/nitrite can also be oxidized in the aqueous solutions found in the atmosphere in the form of fogs, clouds, and particles. Nitrite is well known to be slowly oxidized in the dark to nitrate by dissolved oxygen in the liquid phase. However, it has been reported that the rate of this oxidation increases remarkably during freezing of the solution containing the nitrite (Takenaka et al., 1992, 1996). Figure 7.11, for example, shows the rate of nitrate formation in a nitrite solution at 25°C and in one with the cooling bath at — 21°C (Takenaka et al., 1992). This unusual phenomenon has also been observed with respect to the... 

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