Vapor-gas mixtures

In engineering appHcations, the transport processes involving heat and mass transfer usually occur in process equipment involving vapor—gas mixtures where the vapor undergoes a phase transformation, such as condensation to or evaporation from a Hquid phase. In the simplest case, the Hquid phase is pure, consisting of the vapor component alone. 

A. Bras, G. H. Design of Gooler-Gondensers for Vapor-Gas Mixtures—11, Chem. Eng, p. 238, May (1953). 

Water vapor is frequently removed by pumps that operate with water or steam as a pump fluid, for example, water ring pumps or steam ejector pumps. This depends considerably on circumstances, however, because the economy of steam ejector pumps at tow pressures is generally far inferior to that of rotary pumps. For pumping a vapor - gas mixture in which the vapor portion is large but the air portion is small, the vapor can be pumped by condensers and the permanent gases, by relatively small gas ballast pumps (see Section 2.1.5). 

This is the temperature of a vapor-gas mixture as ordinarily determined by immersion of a thermometer in the gas mixture. 

Dew Point, as was defined earlier, is the temperature at which a vapor-gas mixture becomes saturated when cooled at a constant total pressure out of contact with a liquid. 

In the separation of vapor/gas mixtures, rubbery polymers, such as silicone rubber, can be used to permeate the more condensable vapor components, or glassy polymers can be used to permeate the smaller gases. Although glassy, gas-permeable membranes have been proposed for a few applications, most installed plants use... 

There are many circumstances in which the ability to distinguish the components of a liquid-vapor-gas mixture (or, multiple immiscible liquids, vapors, and gases) in the presence of solids is highly desirable. The liquids and gases do not normally travel at the same velocity. The liquids are being... 

M.-D. Jia, B. Chen, R.D. Noble, and J.L. Falconer, Ceramic-zeolite composite membranes and their application for separation of vapor/gas mixtures, 7. Membrane ScL 90 (1994). 

Adiabatic saturation temperature Final temperature reached by a small quantity of vapor-gas mixture into which water is evaporating. It is sometimes called the thermodynamic wet-bulb temperature. 

If a stream of air is intimately mixed with a quantity of water in an adiabatic system, the temperature of the air will drop and its humidity will increase. If the equilibration time or the number of transfer units approaches infinity, the air-water mixture will reach saturation. The acUabatic saturation temperature T is given by a heat balance between the initial unsaturated vapor-gas mixture and the final saturated mixture at thermal equilibrium ... 

The cyclopropanation of gaseous alkenes, butadiene, and allene (see Section 1.2.1.2.4.2.6.3.3., Table 11, entry 1) by diazoacetic esters can be achieved by passing a vapor-gas mixture of the alkene and the diazo compound at atmospheric pressure through a tubular continuous flow reactor which contains a copper catalyst (ca. 10%) deposited on pumice. In this manner, alkyl cyclopropanecarboxylates were obtained in yields of up to 50% with cop-per(II) sulfate (typical reaction temperature 65-110"C, contact time 3.6 s) or copper(II) oxide (85-200°C, 5s) as catalysts. 

A set of ternary mass transfer experiments was carried out by Toor and Sebulsky (1961b) and Modine (1963) in a wetted-wall column and also in a packed column. These authors measured the simultaneous rates of transfer between a vapor-gas mixture containing acetone, benzene, and nitrogen or helium, and a binary liquid mixture of acetone and benzene. Vapor and liquid streams were in cocurrent flow in the wetted-wall column and in countercurrent flow in the packed column. Their experimental results show that diffusional interaction effects were significant in the vapor phase, especially for the experiments with helium in the wetted wall column. 

A condenser operates with a feed vapor consisting of ammonia(l)-water vapor(2)-hydrogen(3) at a pressure of 340 kPa. At one point in the condenser the mole fractions in the bulk vapor are y n, = 0.30, y2o = 0.40, and y3o = 0.30. The liquid on the condensing surface at this point is at 93.3°C and contains 10 mol% ammonia and 90 mol% water, with negligible hydrogen. The composition of the vapor-gas mixture at the liquid surface, assumed to be in equilibrium with the liquid surface of the stated composition, is y g = 0.455, y2g = 0.195, and y33 = 0.35. Employ the exact matrix solution of the Maxwell-Stefan equations to estimate the rate of condensation of water relative to that of ammonia. 

Your objective here is to examine the influence of turbulence on the interfacial fluxes of acetone(l)-benzene(2)-helium(3) for interphase mass transfer in a wetted wall column at the top of the column where the incoming vapor-gas mixture first comes into contact with the downflowing liquid mixture of acetone and benzene. The details of the column and the operating conditions are given in Example 11.5.3. For the purposes of this exercise you may ignore thermal effects. Take the vapor-phase compositions, expressed in mass fractions, in the bulk vapor and at the interface to be... 

Dew point Temperature value reached when a vapor-gas mixture reaches saturation and condensation occurs during further cooling, for example, condensation of water vapor, q.v. relative humidity (Section 4.2.2). 

A vapor or vapor/gas mixture will condense to a liquid on any surface that is even slightly below the saturation temperature (or dew point) of the vapor at the existing pressure. This is true even if the vapor is highly superheated or multicomponent. In the latter case, the dew point decreases as condensation proceeds. 

Temperature measured by a (dry) thermometer immersed in vapor-gas mixture. 

At present, metallization of dielectrics and semiconductors is carried out either by means of high-temperature, long fusing of metal-containing pastes, or by means of sputtering, condensation at vacuum-thermal evaporation, deposition from vapor-gas mixtures, electroless metallization with preliminary activation by the salts of noble metals, etc. (1-32). 

DEHUMIDIFYING CONDENSERS. A condenser for mixtures of vapors and noncondensable gases is shown in Fig. 15.9. It is set vertically, not horizontally like most condensers for vapor containing no noncondensable gas also, vapor is condensed inside the tubes, not outside, and the coolant flows through the shell. This provides a positive sweep of the vapor gas mixture through the tubes and avoids the formation of any stagnant pockets of inert gas that might blanket the heat-transfer surface. The modified lower head acts to separate the condensate from the uncondensed vapor and gas. 

Dew point is the temperature to which a vapor-gas mixture must be cooled (at constant humidity) to become saturated. The dew point of a saturated gas phase equals the gas temperature. 

Condensation of vapor occurs in a variety of engineering applications. For example, when a vapor is cooled below its saturation temperature, or when a vapor-gas mixture is cooled below its dew point, homogeneous condensation occurs as a fog or cloud of microscopic droplets. Condensation also occurs when vapor comes in direct contact with subcooled liquid such as spraying a fine mist of subcooled liquid droplets into a vapor space or injecting vapor bubbles into a pool of subcooled liquid. The most common type of condensation occurs when a cooled surface, at a temperature less than the local saturation temperature of the vapor, is placed in contact with the vapor. Vapor molecules that strike this cooled surface may stick to it and condense into liquid. 

The heat transfer in the lower part of the sphere is highly nonlinear, and no correlation was reported for this region. Karapantsios and Karabelas [184] experimentally examined the influence of flow intermittency on direct contact condensation of a quasistagnant vapor-gas mixture on falling liquid waves. Flow intermittency was found to increase the heat transfer rate by as much as an order of magnitude. Mikielewicz et al. [218] recently included turbulent diffusion effects in studying direct-contact condensation of steam on a horizontal water film. 

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