Interphase transfer

Strkcttire inflkence. The specificity of interphase transfer in the micellar-extraction systems is the independent and cooperative influence of the substrate molecular structure - the first-order molecular connectivity indexes) and hydrophobicity (log P - the distribution coefficient value in the water-octanole system) on its distribution between the water and the surfactant-rich phases. The possibility of substrates distribution and their D-values prediction in the cloud point extraction systems using regressions, which consider the log P and values was shown. Here the specificity of the micellar extraction is determined by the appearance of the host-guest phenomenon at molecular level and the high level of stmctural organization of the micellar phase itself. 

In preparative selective chromatography, the formation of broad zones of the substances is determined by the formation of sharp boundaries of each zone. The formation of these sharp boundaries of substance zones in column sorption processes for systems in which the interphase transfer is limited by substance diffusion in sorbent grains [104, 122, 123] is determined by the dimensionless criterion X ... 

DillingWL. 1977. Interphase transfer processes. 11. Evaporation rates of chloromethanes, ethanes, ethylenes, propanes, and propylenes from dilute aqueous solutions. Comparisons with theoretical predictions. Environmental Science and Technology 11 405-409. 

Having defined the balance regions, the next task is to identify all the relevant inputs and outputs to the system (Fig. 1.10). These may be well-defined physical flow rates (convective streams), diffusive fluxes, but may also include interphase transfer rates. 

Interfacial area measurement. Knowledge of the interfacial area is indispensable in modeling two-phase flow (Dejesus and Kawaji, 1990), which determines the interphase transfer of mass, momentum, and energy in steady and transient flow. Ultrasonic techniques are used for such measurements. Since there is no direct relationship between the measurement of ultrasonic transmission and the volumetric interfacial area in bubbly flow, some estimate of the average bubble size is necessary to permit access to the volumetric interfacial area (Delhaye, 1986). In bubbly flows with bubbles several millimeters in diameter and with high void fractions, Stravs and von Stocker (1985) were apparently the first, in 1981, to propose the use of pulsed, 1- to 10-MHz ultrasound for measuring interfacial area. Independently, Amblard et al. (1983) used the same technique but at frequencies lower than 1 MHz. The volumetric interfacial area, T, is defined by (Delhaye, 1986)... 

The first two terms on the right side of eq 68 represent the net heat input by conduction and interphase transfer. The first is due to heat transfer between two phases... 

In the previous sections of this book, we focused on the nature of contaminants and the geochemical reactions that can occur in the subsurface environment. Chemical compounds introduced into infiltrating water or in contact with soil or rock surfaces are subject to chemically and biologically induced transformations. Other compounds are retained by the soil constituents as sorbed or bound residues. Thus, in terms of geochemical interactions and reactions among dissolved chemical species, interphase transfer occurs in the form of dissolution, precipitation, volatilization, and various forms of physicochemical retention on the solid surfaces. 

Provide for heat transfer by latent heats of interphase transfer such as by boiling or condensing a component. 

In the latter case, interphase transfer between solid and gas phases in soil appeared to be potentially significant only for two-ring PAH compounds in test systems that represented solid phase treatment of PAH-contaminated soils. Essentially no loss of HMW PAHs occurred. Any mixing or tilling of the soils will therefore likely enhance some volatilization, but by no means affect all of the PAHs. 

The data presented here may be helpful in modeling the environmental fate of surfactants. A recent modeling study for LAS (Mackay et al., 1996) has indicated that, due to negligible gas-water exchange, LAS interphase transfer via the gas phase will not occur. Instead, the aqueous phase is the central compartment for environmental fate of surfactants. Besides biodegradation, which reduces the amount of surfactants in the environment, sorption determines the partitioning of the surfactants between the aqueous and the solid phase. 

OPEN SYSTEM - material is exchanged (e.g. by evaporation) with the surroundings. The system does not have to be OPEN in order to change the amounts of substances present this can occur by chemical reaction or interphase transfer within a closed system. 

Interphase transfer kinetics. At this point, we need to characterize the process that leads to the transfer of the property through the interphase. The transport of the momentum from one phase to another is spectacular when the contacting phases are deformable. Sometimes in these situations we can neglect the friction and the momentum transfer generates the formation of bubbles, drops, jets, etc. The characterization of these flow cases requires some additions to the momentum equations and energy transfer equations. 

The first term in each case arises from bulk flow of gas into the floor of an isolated bubble and out the roof, as required by the hydrodynamic model of Davidson and Harrison (27). The weight of experimental evidence, from studies of cloud size (28,29), from chemical reaction studies (e.g. 30), and from interphase transfer studies (e.g. 31,32), is that this term is better described by the theory proposed by Murray (33). The latter leads to a reduction in the first term by a factor of 3. Some enhancement of the bulk flow component occurs for interacting bubbles (34,35), but this enhancement for a freely bubbling bed is only of the order of 20-30% (35), not the 300% that would be required for the bulk flow term Equations (1) and (2) to be valid. 

It is clear from previous work and from the papers in this symposium that models are much more sensitive to assumptions in some areas than in others. For very slow reactions, rates become controlled by chemical kinetics and insensitive to whatever hydro-dynamic assumptions are adopted (14,48) For intermediate reactions, interphase transfer generally becomes the key factor controlling the reactor performance, with the distribution of gas between phases also playing a significant role. As outlined above, advances have been made in understanding both areas, but models have generally been slow to adopt changes in the basic assumptions used in early bubble models. For fast reactions, the... 

IV. SEPARATION OF MIXTURES BY CHANGING THE DIRECTION OF INTERPHASE TRANSFER... 

Figure 11 Concentration of a more strongly sorbed component (a,b) the process with flow reversal (c,d) the process with changes of interphase transfer direction (a,c) schemes for the process (b,d) distribution of the concentrated component along the column height.

Another example in which change in the interphase transfer direction is made use of is provided by separation processes based on the dependence of selectivity and sorbability of polyfunctional ion exchangers upon the solution pH [33]. 

Other oxides of nitrogen are present in these systems, and they affect the single stage enrichment factor a = ( N/ N)iiquid/( N/ N)gas as well as the interphase transfer rate as measured by the height of the column equivalent to a theoretical plate (HETP). 

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