Vaporization and Condensation

Either mechanism can be used to describe how antimony—halogen systems operate in both the condensed and vapor phases. In the condensed phase a chat that is formed during the reaction of the polymer, antimony trioxide, and the halogen reduces the rate of decomposition of the polymer therefore, less fuel is available for the flame (16). 

Ammonium fluoroborate is both a condensed and vapor-phase flame retardant. It is available from M T Hatshaw, General Chemical Cotp., and Spectmm Chemical Cotp. 

Mechanism. Alumina trihydtate functions as a flame retardant in both the condensed and vapor phases (26). When activated, it decomposes endothermically, eliminating water. 

The mechanism by which tin flame retardants function has not been well defined, but evidence indicates tin functions in both the condensed and vapor phases. In formulations in which there is at least a 4-to-l mole ratio of halogen to tin, reactions similar to those of antimony and halogen are assumed to occur. Volatile stannic tetrahaUde may form and enter the flame to function much in the same manner as does antimony trihaUde. 

Condensation and Vaporization as Effected by Simultaneous Heat and Mass Transfer... 

Precondensers are recommended for any ejector system when the pressure conditions and coolant temperature will allow condensation of vapors, thus reducing the required design and operating load on the ejectors. This is usually the situation when operating a distillation column under vacuum. The overhead vapors are condensed in a unit designed to operate at top column pressure, with only the non-condensables and vapors remaining after condensation passing to the ejector system. 

The sucdon pressure of an ejector is expressed in absolute units. If it is given as inches of vacuum it must be converted to absolute units by using the local or reference barometer. The suction pressure follows the ejector capacity curve, varying with the non-condensable and vapor load to the unit. 

The correlation of Akers, et. al., has given good results in some industrial designs. The authors report that some vertical and inclined tube data is also correlated on the same basis. The sharp break in the data occurs around a Reynolds number of 5 X lO as shown in Figure 10-75. The mass flow rate used to correlate is the arithmetic average of inlet and oudet liquid condensate and vapor flows ... 

Gl and Gg = arithmetic averages of condensate and vapor flow respectively, Ib/hr (ft of flow cross section)... 

This section describes the phase change process for a single component on a molecular level, with both vaporization and condensation occurring simultaneously. Molecules escape from the liquid surface and enter the bulk vapor phase, whereas other molecules leave the bulk vapor phase by becoming attached to the liquid surface. Analytical expressions are developed for the absolute rates of condensation and vaporization in one-component systems. The net rate of phase change, which is defined as the difference between the absolute rates of vaporization and condensation, represents the rate of mass... 

We begin with a discussion of the vapor pressure isotope effect (VPIE). To do so we compare the equilibria between condensed and vapor phase for samples of two isotopomers. At equilibrium, condensed(c) = vapor(v), the partial molar free energies, a(v), and p,(c), of the two phases are equal this, in fact, is the thermodynamic... 

Thermodynamic analysis of VPIE data for separated isotopes (see, e.g., Figs. 7.18a and b) proceeds by equating partial molar free energies in condensed and vapor phases for each isotope. Using Equations 5.1, 5.5 and 5.6 one obtains... 

The standard state Helmholtz free energy difference, 8AA°, was introduced in Equations 5.9 and 5.11 to show the connection between VPIE and molecular structure and dynamics. Molecular properties are conveniently expressed using standard state canonical partition functions for the condensed and vapor phases, Qc° and Qv° remember A0 = —RT In Q°. The Q s are 3nN dimensional, n is the number of atoms per molecule and N is Avogadro s number. For convenience we have now dropped the superscript o s on the Q s. The o s specify standard state conditions, now to be implicitly understood. For VPIE and a respectively, not too close to the critical region,... 

Equation 5.19 relates the molecular energy states of the primed and unprimed isotopomers in condensed and vapor phase to VPIE. The correction terms account for the difference between the Gibbs and Helmholtz free energies of the condensed phase, and vapor nonideality. The comparison is between separated isotopomers at a common temperature, each existing at a different equilibrium volume, V or V, and at a different pressure, P or P, although AV = (V — V) and AP = (P — P) are small. Still, because condensed phase Q s are functions of volume, Q = Q(T,V,N), rigorous analysis requires knowledge of the volume dependence of the partition function, and thus MVIE, since the comparisons are made at V and V. That point is developed later. 

Henry s Law constant for the equilibrium is KH = (Vc/Vg)((t/to) — 1). Vc and Vg are the volumes of condensed and vapor phases in the column (i.e. for gas-liquid chromatography, Vc is the volume of the liquid film on the supported packing or open tubular wall, and Vg the volume of void space, respectively). If the column is in the linear range (small loading) the resolution is,... 

Alternative Reaction Paths, Sn2 and E2 Condensed and Vapor Phase Studies... 

Unlike O, mass dependent fractionation is widespread for Ca in inclusions it ranges from -3.8 to 6.7 %o (Niederer and Papanastassiou 1984) which is about four times the terrestrial range (Schmitt et al. 2003). However, 80% of samples fall within an interval of 2%o. The mass fractionation is the result of complex sequences of condensation and vaporization. The connection to Mg isotopic fractionation is not obvious for these samples as the resolution of Mg measurements is much smaller. 

The working fluid for vapor cycles is alternately condensed and vaporized. When a working fluid remains in the saturation region at constant pressure, its temperature is also constant. Thus, the condensation or evaporation of a fluid in a heat exchanger is a process that closely approximates the isothermal heat-transfer processes of the Carnot cycle. Owing to this fact, vapor cycles closely approximate the behavior of the Carnot cycle. Thus, in general, they tend to perform efficiently. 

Four classes of this kind of equipment are considered heat exchangers without phase change, steam heaters, condensers, and vaporizers or reboilers. These arc grouped together with descriptions in Figures 3.8-3.11. Where applicable, comments are made about the utility of the particular method. In these heat... 

Boron Mechanism. Boron functions as a flame retardant in both the condensed and vapor phases. Under flaming conditions boron and halogens form the corresponding trihalide. Because boron (rihalides are effective Lewis acids, they promote cross-linking, minimizing decomposition of the polymer into volatile flammable gases. These trihalides arc also volatile thus they vaporize into the (lame and release halogen which Ihen functions as a Maine inhibitor. 

However, as heating continues, the vapor condenses and vaporizes over and over as it rises the liquid drips back into the boiling mixture. The vapor becomes richer in the component with the lower boiling point as it continues to rise through the column and passes out into the condenser. Therefore, the final distillate is pure benzene, the more volatile of the components, whereas the liquid in the pot is pure toluene. 

From a careful analysis of the condensed- and vapor-phase components in the range 813 to 973 K, Oza and Patel119 deduce the following reaction sequence ... 

The new lunatic showed great willingness to assist in the practical ventures of his fellows. Even if Priestley had not been inclined to help Boulton and Watt, Boulton s patronage gave some leverage, which he was prepared to use if necessary. Thus, in relation to experiments on the possibilities of deriving mechanical power from the repeated condensation and vaporization of airs derived from fixed alkali, Boulton wrote to Watt ... 

The objective in analyzing these units is to calculate the temperature, the conqjosition, and the flow rates of the vapor and hquid exit streams, given the properties of the entering streams. First, write the mole balances. For two components, we write two component balances and a mole fraction summation for each unknown stream as given by Equations 3.3.1 to 3.3.4 in Table 3.3.1. There are two phases in equilibriiun leaving the valve, condenser and vaporizer, although the phases have not, as yet, been separated. A phase separator will separate the phases. For a vaporizer, both component and phase separation occur in the same process unit. As stated before, the first numerical subscript is the line number and the second the component number. We also identify the phases by an additional subscript, V for vapor and L for liquid. Because we are assuming equilibrium between the vapor and liquid for each component downstream of the valve, we can... 

One sees from the above development that our eventual interest lies in correlating the observed isotope effects with the detailed motions of the molecule in the condensed and vapor phases—i.e., with a microscopic model. Others—e.g., see References 8, 9, 11, 12, and 15—have made the alternate choice of bypassing a model and reporting the results directly in terms of the isotope effects on the thermodynamic parameters... 

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