Adiabatic expansion, condensation

These mechanisms can be observed in many common situations. For example, fog via mixing can be seen in the discharge of breath on a cold day. Fog via adiabatic expansion can be seen in the low-pressure area over the wing of an airplane landing on a humid summer day and fog via condensation can be seen in the exhaust from an automobile air conditioner (if you follow closely enough behind another car to pick up the ions or NO molecules needed for nucleation). All of these occur at a veiy low supersaturation and appear to be keyed to an abundance of foreign nuclei. All of these fogs also quickly dissipate as heat or unsaturated gas is added. 

This cloud of fog is due to a significant drop in temperature in the headspace below the champagne surface, caused by the sudden gas expansion when the bottle is uncorked. Actually, this sudden temperature drop is responsible for the instantaneous condensation of water vapor into the form of this characteristic cloud of fog. Assuming an adiabatic expansion experienced by the gas volume of the headspace (from about 5 to 1 atm), the corresponding theoretical drop in temperature experienced by the gas volume may easily be accessed by the following and well-known relationship ... 

AnnPhys 10(IV), 645(1925) (Spherical detonations of CS2+3O2 mixture) 2) L.D. Landau K.P. Stanyukovich, DoklAkadN 46, 399(1945) (On the study of detonation in condensed explosives) 3) H. Jones Sc A.R. Miller, PrRoySoc 194A, 480-507(1948) (The detonation of solid explosives The equilibrium conditions in the detonation wave-front and the adiabatic expansion of the products of detonation) 3a) Cole, Underwater (1948), pp 81-83 4) J. 

As mentioned earlier, experiments indicate that spontaneous condensation is not significant until fairly high supersaturations are achieved. For example, supersaturations of slightly less than 5 are necessary with water vapor in particle free air for the formation of a visible fog by adiabatic expansion of moist air at 0°C. This supersaturation implies a critical droplet diameter of about 0.0015 xm and a cluster of several hundred molecules. 

II. Cp<0. If the vapour is to remain saturated during compression, we must withdraw heat from it. An adiabatic compression will, therefore, cause the vapour to become unsaturated or superheated, an adiabatic expansion will produce partial condensation. 

How does an initially unsaturated vapor, represented by a point Lo the right of the vapor pressure curve, reach conditions under which condensation can occur Any number of paths on the [p, T) diagram are imaginable, but two are of particular interest reversible adiabatic expansion and mixing with cooler air at a lower concentration. Both proces.ses may lead 10 the formation of an aerosol composed of small liquid droplets. The paths Followed... 

Ga.s-to-particie conversion may result from homogeneous gas-phase processes, or it may be controlled by processes in the particulate phase. Gas-phase processes, either physical or chemical, can produce a supersaturated state which then collapses by aero,s ol formation. Physical processes producing supersaturation include adiabatic expansion or mixing with coo air—-discussed in the last chapter—or radiative or conductive cooling. Gas-phase chemical reactions such as the oxidation of SO2 to sulfuric acid in the atmosphere or the oxidation of SiCU to SiOi in industry also generate condensable products. 

Sotitnition Rettto 249 Cofuienscition hy Adiabatic Expansion 2S1 Condensation hy i ixin t 252 Eifect of Solutes on Vapor Pressure 254 Vapor Pressure of a Small Particle 256 77ie Kidvin Relation 256... 

Goto, T., Futamura, Y., Yamaguchi, Y. et al. (2005). Condensation reactions of amino acids under hydrothermal conditions with adiabatic expansion cooling. Journal of Chemical Engineering of Japan, 38,4 295-9. 

When transformation of a less stable into a more stable phase occurs, the change does not take place at one moment throughout the whole phase, but proceeds from definite points or growth centres (nuclei). Such nuclei may form spontaneously in a supercooled phase, as is seen, for example, in the cloud formation produced on the cooling of a vapour by adiabatic expansion. The influence of dust particles and of gaseous ions in increasing the number of condensation nuclei, is well known. 

As a further stage to ensure the removal of any small particles of dust, flue gas can be directed to a Venturi-type dust collector. At both the Met and the outlet of this type of collector, dust is covered by condensate through adiabatic expansion and collected by sprayed water that is circulated via tanks installed at the inlet and the outlet, respectively. This system is also a useful preparation for the removal of traces of sulfur dioxide by passing the gases through an absorber tower where the sulfur oxides are removed by contact with circulating water that is sprayed into the tower. 

The operating pressure for cryogenic distillation of air is established so that feed air can be partially liquefied at a temperature achievable by adiabatic expansion of the feed gas. Intermediate pressures are set so that efficient reboiling and condensing can be combined in a single heat exchanger at the temperatures encountered in the process. This avoids the inefficiencies and... 

The original equations discussed earlier take into account heat transfer by conduction and convection, heat of evaporation and condensation, capillary effect and Darcy s law, but they ignore the Joule-Thomson effect and the temperature effect of adiabatic expansion of formation liquids and gases. 

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