Drops Spray Condensers

In many cases, heating or cooling of the gaseous effluent will be required before if enters the control device. The engineer must be thoroughly aware of the gas laws, thermodynamic properties, and reactions involved to secure a satisfactory design. For example, if a gas is cooled there may be condensation if the temperature drops below the dewpoint. If water is sprayed into... 

The term mist generally refers to liquid droplets from submicron size to about 10 /xm. If the diameter exceeds 10 /xm, the aerosol is usually referred to as a spray or simply as droplets. Mists tend to be spherical because of their surface tension and are usually formed by nucleation and the condensation of vapors (6). Larger droplets are formed by bursting of bubbles, by entrainment from surfaces, by spray nozzles, or by splash-type liquid distributors. The large droplets tend to be elongated relative to their direchon of mohon because of the action of drag forces on the drops. 

Mists and sprays also affect flammability limits.12 For suspensions with drop diameters less than 0.01 mm, the LFL is virtually the same as the substance in vapor form. This is true even at low temperatures where the liquid is nonvolatile and no vapor is present. Mists of this type are formed by condensation. 

In contrast to the large variety of averages and measures of dispersion prevalent in the literature, the number of basic distributions which have proved useful is relatively small. In droplet statistics, the best known distributions include the normal, log-normal, Rosin-Rammler, and Nukiyama-Tanasawa distributions. The normal distribution often gives a satisfactory representation where the droplets are produced by condensation, precipitation, or by chemical processes. The log-normal and Nukiyama-Tanasawa distributions often yield adequate descriptions of the drop-size distributions of sprays produced by atomization of liquids in air. The Rosin-Rammler distribution has been successfully applied to size distribution resulting from grinding, and may sometimes be fitted to data that are too skewed to be fitted with a log-normal distribution. 

If the temperature of a liquid is below its flash point, flammable concentrations of vapor cannot exist, but conditions still can exist for flammability if mists or foams are formed. A suspension of finely divided drops of a flammable liquid in air has many of the characteristics of a flammable gas-air mixture and can bum or explode. A mist may be produced by condensation of a saturated vapor or by mechanical atomization. Normally, the diameter of drops in a condensed mist is less than 0.01mm, whereas in a mechanical spray it usually is greater than 0.1 mm. 

Assay Dissolve about 0.4 g of sample, previously dried at 105° for 4 h and accurately weighed, in about 300 mL of water contained in a 500-mL round-bottom flask. Add 3 g of a powder of Devarda s alloy and 15 mL of a 40% sodium hydroxide solution, and connect with a spray-preventing device and condenser to the flask. Allow to stand for 2 h. Transfer 50 mL of 0.1 N sulfuric acid into a receptacle, use this to collect 250 mL of the distillate, and titrate the excess sulfuric acid with 0.1 IV sodium hydroxide, using 3 drops of methyl red-methylene blue TS as the indicator. Perform a blank determination (see General Provisions), and make any necessary correction. Each milliliter of 0.1 A sulfuric acid is equivalent to 10.11 mg of KNO3. 

Evaporation of liquid drops is equally important. For example, in the application of a pesticide by spraying, it is desired that evaporation be minimized to increase the amount of pesticide reaching the plants. Yet in the production of such foodstuffs as powdered milk or powdered coffee, product quality is improved when evaporation proceeds as quickly as possible. In sampling aerosols, evaporation or condensation may alter aerosol size distribution and affect operation of the sampling instrument. In this case it is desired that static conditions be maintained if at all possible. 

Path The entering liquid temperature is below the dew point of the entering air. The temperature of the air contacted by the cold spray drops below the dew point (the path again moves to the left), and water vapor condenses out of the air (the path moves down). 

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