Fractionation condenser fogging

When aluminized AP composite propellant burns, a high mole fraction of aluminum oxide is produced as a combustion product, which generates visible smoke. If smoke has to be avoided, e. g. for miUtary purposes or a fireworks display, aluminum particles cannot be added as a component of an AP composite propellant In addition, a large amount of white smoke is produced even when non-aluminized AP composite propellants bum. This is because the combustion product HCl acts as a nucleus for moisture in the atmosphere and relatively large-sized water drops are formed as a fog or mist This physical process only occurs when the relative humidity in the atmosphere is above about 60%. If, however, the atmospheric temperature is below 260 K, white smoke is again formed because of the condensation of water vapor with HCl produced as combustion products. If the HCl smoke generated by AP combustion cannot be tolerated, the propellant should be replaced with a double-base propellant or the AP particles should be replaced with another... 

AP composite propellants without aluminum particles are termed reduced-smoke propellants and are employed in tactical missiles to conceal their launch site and flight trajectory. No visible smoke is formed when the relative humidity of the atmosphere is less than about 40%. However, since high-frequency combustion oscillation tends to occur in the combustion chamber in the absence of solid particles that serve to absorb the oscillatory energy, a mass fraction of 0.01-0.05 of metallic particles is still required for the reduced-smoke propellants. These particles and/or their oxide particles generate thin smoke trails. The white smoke trail includes the white fog generated by the HCl molecules and the condensed water vapor of the humid atmosphere. 

Atmospheric aerosols are important nuclei for the condensation of water droplets (cloud, rain, fog). The dissolution of the water-soluble aerosol components contributes to the composition of the aqueous phase [e.g., NH4NO3, (NH4)2S04]. Aerosols may contain, in addition to the absorbed gases, a substantial fraction of atmospheric components that return ultimately to the earth surface by dry or wet deposition. The particle diameter ranges from 0.01 nm up to a few hundred micrometers. Primary atmospheric aerosols consist of dust and smoke particles while secondary aerosols are made up of constituents of the gas phase. 

The concentration of acetic acid in the fog fraction is essentially identical with the concentration at the maximum boiling point as only the molecules of the TEA/acetic acid complex undergo condensation. 

Table 8-6 presents an overview on the concentrations of the major ions in rainwater observed at various locations. Table 8-7 provides some information on cloud and fog waters. In maritime regions seasalt is an important source of cloud condensation nuclei, and it undergoes effective below-cloud scavenging as well. Sodium chloride accordingly contributes the largest fraction of all ions in rainwater. Some of the other ions usually are somewhat enriched in comparison with their relative abundances in seasalt. The enrichment of potassium and calcium is due to the admixture of aerosol from continental sources, and that of sulfate arises from the oxidation of gaseous precursors such as dimethyl sulfide of S02- This excess sulfate is associated almost exclusively with submicrometer-sized particles (see Section 7.5.1). 

The term e/(ee — 1), which appears in equations 1 and 2, was first developed to account for the sensible heat transferred by the diffusing vapor (1). The quantity 8 represents the group M4-C 4 / hg, the ratio of total transported energy to convective heat transfer. Thus it may be thought of as the fractional influence of mass transfer on the heat-transfer process. The last term of equation 3 is the latent heat contributed to the gas phase by the fog formation. The vapor loss from the gas phase through both surface and gas-phase condensation can be related to the partial pressure of the condensing vapor by using Dalton s law and a differential material balance. 

---