Interface, component transfer

Component Transfer Properties Interface component transfer... 

In the Fangmuir-Blodgett technique, amphiphilic monolayers, formed at a liquid-air interface, are transferred to a solid substrate by horizontal or vertical transfer. The thickness of such monolayers is of the order of a few nanometers, depending on the materials being used. With this method, multilayer structures can also be produced, either by repeated deposition of the same layer or by the deposition of alternate layers. In this manner, multilayers containing several hundred individual components can be obtained. In general, the thermal and mechanical stabilities of such layers are, however, limited. 

The removal of one of more selected components from a mixture of gases by absorption into a suitable solvent (Mass Separating Agent, MSA) is the second major operation of chemical engineering after distillation. Absorption is based on interface mass transfer controlled largely by rates of diffusion. It is worth noting that absorption followed by a chemical reaction in the liquid phase is often used to get more removal of a solute from a gas mixture. 

Abstract The objective of this chapter is to present some recent developments on nonaque-ous phase liquid (NAPL) pool dissolution in water saturated subsurface formations. Closed form analytical solutions for transient contaminant transport resulting from the dissolution of a single component NAPL pool in three-dimensional, homogeneous porous media are presented for various shapes of source geometries. The effect of aquifer anisotropy and heterogeneity as well as the presence of dissolved humic substances on mass transfer from a NAPL pool is discussed. Furthermore, correlations,based on numerical simulations as well as available experimental data, describing the rate of interface mass transfer from single component NAPL pools in saturated subsurface formations are presented. 

Numerous empirical correlations for the prediction of residual NAPL dissolution have been presented in the literature and have been compiled by Khachikian and Harmon [68]. On the other hand, just a few correlations for the rate of interface mass transfer from single-component NAPL pools in saturated, homogeneous porous media have been established, and they are based on numerically determined mass transfer coefficients [69, 70]. These correlations relate a dimensionless mass transfer coefficient, i.e., Sherwood number, to appropriate Peclet numbers, as dictated by dimensional analysis with application of the Buckingham Pi theorem [71,72], and they have been developed under the assumption that the thickness of the concentration boundary layer originating from a dissolving NAPL pool is mainly controlled by the contact time of groundwater with the NAPL-water interface that is directly affected by the interstitial groundwater velocity, hydrodynamic dispersion, and pool size. For uniform... 

Since the source pressure has to be maintained within the pumping capacity or conductance of the vacuum system, low carrier gas flow rates are necessary or various types of interface are used to reduce the carrier gas component in the GC effluent. Interfaces and transfer lines have to be maintained at or above the maximum column temperature used. 

The best known model for slugging fluidized beds is that of Hovmand and Davidson (45,46). This is a variant on the Orcutt model (17,18) (see also Table 2) which assumes plug flow of gas in the dense phase. The interface mass transfer is again composed of two parts, a throughflow component and a diffusional component, with the dimensionless mass transfer coefficient given approximately by... 

When components are transferred across a liquid-Uquid or a liquid-gas interface A, in each phase, owing to the resistance to component transfer, a concentration gradient will occur. In the model that describes this interfacial transfer, it is assumed, as shown in Fig. 2.14, that the concentration gradient restricts itself to a boimdary layer. 

A simple treatment is stiU possible if it may be assumed that the flux of the component of interest A through the interface stays in a constant proportion to the total molar transfer through the interface over the entire tower ... 

When the soHd substrate is placed in the bath, the air is displaced by the bath, fl, and the 37T interface is replaced by an SB interface. Similarly, an interface replaces the interface. The equiHbrium free energy values of these new interfaces are not estabHshed immediately but gradually through mass transfer (if there is any mutual solubiHty between F and fl it is assumed that B does not dissolve 3) and through adsorption of dissolved components. When these processes have gone to completion the new relationship is... 

The electrostatic behavior of intrinsically nonconductive substances, such as most pure thermoplastics and saturated hydrocarbons, is generally governed by chemical species regarded as trace contaminants. These are components that are not deliberately added and which may be present at less than detectable concentrations. Since charge separation occurs at interfaces, both the magnitude and polarity of charge transfer can be determined by contaminants that are surface active. This is particularly important for nonconductive liquids, where the electrostatic behavior can be governed by contaminants present at much less than 1 ppm (2-1.3). 

One example of normal-phase liquid chromatography coupled to gas chromatography is the determination of alkylated, oxygenated and nitrated polycyclic aromatic compounds (PACs) in urban air particulate extracts (97). Since such extracts are very complex, LC-GC is the best possible separation technique. A quartz microfibre filter retains the particulate material and supercritical fluid extraction (SPE) with CO2 and a toluene modifier extracts the organic components from the dust particles. The final extract is then dissolved in -hexane and analysed by NPLC. The transfer at 100 p.1 min of different fractions to the GC system by an on-column interface enabled many PACs to be detected by an ion-trap detector. A flame ionization detector (PID) and a 350 p.1 loop interface was used to quantify the identified compounds. The experimental conditions employed are shown in Table 13.2. 

Where heat transfer is taking place at the saturation temperature of a fluid, evaporation or condensation (mass transfer) will occur at the interface, depending on the direction of heat flow. In such cases, the convective heat transfer of the fluid is accompanied by conduction at the surface to or from a thin layer in the liquid state. Since the latent heat and density of fluids are much greater than the sensible heat and density of the vapour, the rates of heat transfer are considerably higher. The process can be improved by shaping the heat exchanger face (where this is a solid) to improve the drainage of condensate or the escape of bubbles of vapour. The total heat transfer will be the sum of the two components. 

The gaseous components must be transferred from the bulk gaseous phase to the bulk liquid phase. The components are transferred to the gas-liquid interface by convection and diffusion in the gas and from the interface by diffusion and convection in the liquid. 

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