Big Chemical Encyclopedia

Chemical substances, components, reactions, process design ...

Articles Figures Tables About

Vapors Containing Noncondensable Gases

Condensation of Vapors Containing Noncondensable Gases The presence of noncondensable gases in a vapor decreases the rate of heat transfer. This reduction depends upon the relative values of the gas-cooling heat load and the total cool-Ing/condensing heat duty. [Pg.25]

One mechanism for the analysis of condenser/coolers assumes that the latent heat of condensation Is transferred only through the condensate film, whereas the gas-cooling duty Is transferred through both the gas and condensate films. This mechanism yields good results for cases in which the condensate and cooling vapor-gas mixture are in substantial equilibrium. This mechanism applies only when the condensing surface is colder than the dew point of the mixture. [Pg.25]

Some comments on these equations must be made  [Pg.26]


Algorithm 11.1 may be adapted as Algorithm 15.1 to determine the set of temperatures, mole fractions, and fluxes that makes the discrepancy functions close to zero. An illustration of this algorithm is provided by Example 15.1.1. One of the advantages of the simultaneous solution procedure is that, as shown in Example 15.1.2, only minor modifications of it are needed if the vapor contains noncondensing gases. [Pg.441]

In practice, the vapor that is to be condensed sometimes contains noncondensible gases such as air. The presence of these noncondensible gases can significantly lower the heat transfer rate from that which would exist under the same circumstances with a pure vapor. A common example is the build-up of air in power plant condensers. These condensers usually operate at a substantial vacuum and some air entrainment is unavoidable. The continuous removal of air by specially designed ejector systems is essential to maintain the condenser vacuum and to maintain acceptable condensation rates. In some chemical plants, the separation of constituents is sometimes produced by condensing one gas from a mixture of gases and in such cases the presence of a noncondensible gas is unavoidable. [Pg.585]

The basic design of a heat pipe may be modified to operate as a temperature-control device, as shown in Fig. 12-21. A reservoir containing a noncondensible gas is connected to the heat-removal end of the heat pipe. This gas may then form an interface with the vapor and choke off part of the condensation to the wick. With increased heat addition, more vapor is generated with an increase in vapor pressure, and the noncondensible gas is forced back into the reservoir, thereby opening up additional condenser area to remove the additional heat. For a reduction in heat addition, just the reverse operation is... [Pg.625]

The gas-liquid permporometry combines the controlled stepwise blocking of membrane pores by capillary condensation of a vapor, present as a component of a gas mixture, with the simultaneous measurement of the free diffusive transport of the gas through the open pores of the membrane. The condensable gas can be any vapor provided it has a reasonable vapor pressure and does not react with the membrane. Methanol, ethanol, cyclohexane and carbon tetrachloride have been used as the condensable gas for inorganic membranes. The noncondensable gas can be any gas that is inert relative to the membrane. Helium and oxygen have been used. It has been established that the vapor pressure of a liquid depends on the radius of curvature of its surface. When a liquid is contained in a capillary tube, this dependence is described by the Kelvin equation, Eq. (4-4). This equation which governs the gas-liquid equilibrium of a capillary condensate applies here with the usual assumption of a=0 ... [Pg.108]

How can you predict the properties of a mixture of a pure vapor (which can condense) and a noncondensable gas at equilibrium A mixture containing a vapor behaves somewhat differently than does a pure component by itself. A typical example with which you are quite familiar is that of water vapor in air. [Pg.298]

Condensation occurs whenever a vapor, a vapor mixture, or a vapor containing a noncondensable gas is brought into contact with a surface below the dew point or saturation temperature of the vapor. The condensed liquid is most likely to form a continuous film covering the cooled surface. In some cases, however, dropwise condensation is possible if the fluid does not wet the surface. Filmwise condensation is encountered in most industrial applications and is the only mode of condensation we shall consider further. [Pg.435]

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. [Pg.440]

All vapors to be condensed contain noncondensables. A vapor containing as little as 100 ppm noncondensables can fill a reboiler up with noncondensable gas within less than 10 h if there is no venting (28). [Pg.465]

Suppose that an ideal solution of two components (i = 1,2) is in the presence of a noncondensable gas (subscript g). Neglecting the solubility of the gas in the liquid, the liquid contains only the liquid components while the gas contains the noncondensable gas well as vapors of the liquid components. The vapor/liquid equilibrium of the condensable components is described by Raoult s law ... [Pg.401]

The scope of psychrometry is the detailed study of gas-vapor mixtures, where gas refers to a noncondensing gaseous compound for the temperature range considered, while vapor refers to a gaseous phase in thermodynamic equilibrium with its liquid state. In the particular case where the gas is dry air, and the vapor is water vapor (i.e., steam), it is called hygrometry, and the mixture is called moist air. As a general rule, the humidity is the amount of water vapor contained in the dry air. The total pressure of the water-air mixture is described by the summation of partial pressures of each individual gas such as in the following Dalton s equation ... [Pg.1054]

Processes that handle light hydrocarbons can suffer from a buildup of noncondensible materials. For example, if liquid propane is added to a pressure vessel, a vapor space will form at the top of the vessel. If the propane contains a small amount of noncondensible gas such as nitrogen, that gas will accumulate in the... [Pg.350]

If flux measurements are started when the relative vapor pressure of the eon-densable gas equals unity, all the pores in the membrane should be elosed (i.e., filled with condensed liquid), avoiding any diffusive flux of the noneondensable gas through the membrane. When the relative vapor pressure is slightly below unity the liquid contained in the largest pores starts to vaporize diereby opening these pores. The Kelvin equation allows correlation of die relative pressure with the size of the pores opened to flux (Kelvin radius, ). The measured flow of the noncondensable gas can be easily translated in terms of pore number onee die appropriate gas transport model is taken into account. By decreasing steadily die relative pressure until all the pores are opened, both the differential and integral pore size distributions can be obtained. [Pg.383]

The dew-point temperature of a gas (vapor) may be found using a method similar to that for bubble-point temperature estimation. Again, suppose a gas phase contains the condensable components A, B. C. .. and a noncondensable component G at a fixed pressure P. Let y/ be the mole fraction of component i in the gas. If the gas mixture is cooled slowly to its dew point, Tdp, it will be in equilibrium with the first liquid that forms. Assuming that Raoult s law applies, the liquid-phase mole fractions may be calculated as... [Pg.260]

Approximately 1 of air enters the extractor with each 1 of material. To maintain the extractor under a slight vacuum, the air must be continuously vented from the extractor. At the extractor temperature of 60°C, an equilibrium condition will occur where the vent gas exiting the extractor will contain approximately 10 parts of solvent vapor for every one part of air (see Figure 12). The solvent vapor and air exit the extractor and are typically condensed in an extractor condenser. The extractor condenser is a shell and tube vessel with the vapors typically on the shell side and the coohng water on the tube side. The noncondensable vapors exiting the extractor condenser pass on to the vent condenser. [Pg.2507]


See other pages where Vapors Containing Noncondensable Gases is mentioned: [Pg.331]    [Pg.2299]    [Pg.143]    [Pg.14]    [Pg.89]    [Pg.142]    [Pg.158]    [Pg.8]    [Pg.2054]    [Pg.1325]    [Pg.2591]    [Pg.4]    [Pg.530]    [Pg.138]    [Pg.929]    [Pg.1324]    [Pg.2571]    [Pg.2303]    [Pg.4]    [Pg.456]    [Pg.666]    [Pg.783]    [Pg.8]    [Pg.351]    [Pg.561]    [Pg.167]    [Pg.1048]    [Pg.2191]    [Pg.84]    [Pg.226]    [Pg.1205]    [Pg.48]    [Pg.871]    [Pg.1947]    [Pg.430]    [Pg.1214]    [Pg.2441]   


SEARCH



Containment vapor

Gases vaporization

Noncondensable

Noncondensable gases

Noncondensible gas

Noncondensibles

Vapors gases

© 2024 chempedia.info