Condensers fogging

Lm. The coarseness results from the relatively low power dissipation per mass on distillation trays. This means that it is relatively easy to remove by a device such as a wire mesh pad. Over 50 percent is typically captured by the underside of the next higher tray or by a turn in the piping leaving an evaporator. Conversely, though small on a mass basis, the smaller drops are extremely numerous. On a number basis, more than one-half of the drops in the lower curve are under 5 [Lm. These can sei ve as nuclei for fog condensation in downstream equipment. 

Fog Condensation This is an entirely different way of forming dispersions. Here, the dispersion results from condensation of a vapor rather than mechanical breakup. The particle sizes are usually much finer (0.1 to 30 Im) and are designated as mist or fog. 

Jons. Amelin [Theory of Fog Condensation, Israel Program for Scientific Translations, Jerusalem, (1967)] reports that ordinary air contains even higher concentrations of ions. These ions also reduce the required critical supersaturation, but by only about 10 to 20 percent, unless multiple charges are present. 

Fog Condensation—The Other Way to Make Little Droplets For a variety of reasons, a gas or vapor can become supersaturated with a condensable component. Surface tension and mass transfer impose barriers on immediate condensation, so growth of fog particles lags behind what equilibrium predicts. Droplets formed by Fog condensation are usually much finer (0.1 to 10 pm) than those formed by mechanical breakup and hence more difficult to collect. Sometimes fog can be a serious problem, as in the atmospheric discharge of a valuable or a hazardous material. More commonly, fog is a curiosity rather than a dominating element in chemical processing. 

Amelin, A. G., Theory of Fog Condensation, Israel Program for Sci. Trans., Jerusalem, 1967. 

Evidence was found for the major processes responsible for the acidification of fogwater (i) the scavenging of acidic precursor aerosol, (ii) the scavenging of gaseous nitric acid, and (iii) oxidation of reduced sulfur components to sulfate. Conversion of S02(g) to sulfate in fogwater does not appear to proceed faster than 10% hour" and therefore cannot account for the high acidities observed at the beginning of fog events however, sulfate production in the precursor air parcel can lead to sulfuric acid fog condensation nuclei. 

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