Heavy clouds

Colorless gas that forms heavy clouds in moist air. It has a sharp, irritating and suffocating odor similar to hydrogen chloride. This material is hazardous through inhalation and produces local skin/eye impacts. 

Two volunteers exposed to a concentration of Img/m for 8 hours developed a persistent cough, which lasted for 8 days 21 days after the original exposure, reexposure for 5 minutes to a heavy cloud of vanadium pentoxide dust occurred and, within 16 hours, marked cough developed the following day, rales and expiratory wheezes were present throughout the entire lung field, but pulmonary function was... 

Similarly, titanium tetrachloride (TiCl 4) rapidly reacts with moist air to produce a heavy cloud of titanium hydroxide - Ti(OH) - and HCl. 

The density of the cloud or plume and its interaction with the ambient air affect the dispersion process. A buoyant cloud has a density less than that of the surrounding air. A heavy cloud has a density greater than the surrounding air. The density of a neutrally buoyant cloud is equal to that of the surrounding air. 

Over the European continent, the North-Atlantic cyclones weaken during their eastward propagation, but often they cause the weather to be quite variable. That means, a very diverse but usually heavy cloud cover with occasional precipitation prevails over the Baltic Sea. It is generally moist, cool, and rather windy. The global west-wind jet carries moist and cool air masses from the North Atlantic and the North Sea to central and northern Europe (Nehring et al., 1990). This leads to a predominantly maritime influence on the Baltic Sea region. This... 

Colorless gas very pungent odor similar to that of hydrogen chloride. Forms heavy clouds with moist air. Dec by water into silicic acid and HF. Sublimes —95.7 mp —90.2 ... 

The summer sun was blazing over the southern part of the city and the city center was covered with black smoke and fire, which kept shooting up to the sky like a tornado. The place where we were was dark with heavy clouds hanging over our heads. The entire city looked like a hell on earth. ... 

Most of the heavier-than-air cloud field experiments have focused on the dispersion of gaseous clouds. However, some experiments have been conducted with two-phase effects, e.g., the Desert Tortoise, Eagle, Goldfish series (Koopman et al., 1989) and FLADIS field experiments (Nielsen et al., 1997). In particular, the Desert Tortoise series was designed to study the dispersion of two-phase ammonia clouds. It was reported that two-phase effects had a dominating influence on the temperature and spreading behavior of the cloud and the extent of the heavy cloud dispersion regime (Koopman et al., 1986). Recently, available field data sets have been reviewed within the SMEDIS (Scientific Model Evaluation of Dense Gas Dispersion Models) project (Daish et al., 1998 Carissimo et al., 1999). 

We have illustrated the model predictions by evaluating two-phase ammonia clouds released in dry and moist air. The numerical test cases are identical to those in Kukkonen et al. (1993), which presents a comparison of the model AERCLOUD and the thermodynamical submodel of the heavy cloud dispersion program DRIFT (Webber et al., 1992). DRIFT embodies the homogeneous equilibrium model, while AERCLOUD allows also for thermodynamic nonequilibrium effects. Both models will cope with ammonia interactions with moist air as well as with the simpler dry air problem. 

Similarly, titanium tetrachloride (TiCl4) rapidly reacts with moist air to produce a heavy cloud of titanium hydroxide—Ti(OH)4— and HCl. Obviously, the hydrogen chloride gas that is produced will pick up moisture from the atmosphere to form hydrochloric acid, so this must be factored into decisions on where and how to deploy such a smoke cloud. 

As disperse systems with solid disperse phase may be cited snow clouds, smoke, cosmic dust, and volcanic ashes. The latter are often so fine that they may be carried hundreds of miles by the wind, and become the cause of striking and beautiful color displays in the heavens. Not infrequently has it destroyed large tracts of land, and cities with their inhabitants. Herculaneum and Pompeii fell victims to a rain of ashes while St. Pierre was destroyed by a nufe ardente, a hot heavy cloud composed of air, steam, small stones, sand, and dust. The dust was in such a state of fine division that it fell to the groimd during the descent of the cloud. ... 

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