Vapor-phase flux

Viability of Starch Derivatives as Flavoring Encapsulants. The capillary GC vapor phase flux term (defined by a percent external standard or ZEStD flux) previously described (34) was used to screen starch derivatives (oxidized, dextrinized and/or covalent amino acid linkage) as to their flavor encapsulation potential. The samples were prepared as previously described (34) with the exception of an added reduced pressure deaeration step, thus allowing the use of the headspace diffusivity versus retention standard curves to predict volatile lemon oil retention following spray drying. 

Following preliminary hypochlorite treatments, a coherent process path was identified and implemented. Corn starch was oxidized with 6.4% (w/w) hypochlorite for two hours and given a combined base-heat gelatinization process (Method A). This base material exhibited excellent physical characteristics (i.e., stable emulsion with 20% db lemon oil incorporation into an aqueous dispersion, low lemon oil vapor phase flux (low headspace content), lack of inherent flavor and aroma) and when finally tested for spray dried lemon oil (20% db) retention efficiency in a lab-scale mini-dryer, the viability of this polymer was ascertained. Nearly 70% of the added lemon oil was retained following the drying of this DE 1.45 starch, a measure of functionality matched only by gum arabic (34). 

Characterization of both the Control and Oxidized starches was completed by examining emulsion stabilty, vapor phase flux, dryer retention values of added lemon oil (Table II),... 

The finished polymer was to act as an "improved" wall material and, therefore, the ablity of this polymer to reduce the vapor-phase flux of lemon oil (from an aqueous sample) was the preselected flagging procedure. 

Protein attachment (i.e., casein and gelatin) to a DE 10 maltodextrin base failed to yield any substantial improvement in hindering lemon oil vapor phase flux using mole ratios of 0,... 

Table III, influence of Binding Amino Acids to Maltodextrins on Lemon Oil Vapor Phase Flux...

Table IV. Vapor phase flux and dryer retentions of lemon oil incorporation (20%j5) into selected glycoamine polymers and their base materials...

Substantial improvement (about 50%) of lemon oil encapsulation efficiency was attained for the covalently-linked phenylalanine-Oxidized starch wall material over the Oxidized starch control. In fact, this particular glycoamine resulted in lemon oil retentions following drying in the mini-spray dryer which surpassed both the Control and lipophilic starches (See Table IV). Dry blending phenylalanine with the Oxidized starch base exhibited the benefits associated with covalently linked glycoamine production via lemon oil vapor phase flux analysis. 

Solid/vapor interface motion can be produced by evaporation—the atoms that compose the solid phase are removed from the surface via the vapor phase reverse motion can be produced by condensation where a vapor-phase flux is directed onto the solid phase. Figure 14.2 illustrates how simultaneous evaporation and condensation can result in surface smoothing. 

The vapor phase flux evaporation (atmospheric air in the majority, could be nitrogen)... 

CoF is used for the replacement of hydrogen with fluorine in halocarbons (5) for fluorination of xylylalkanes, used in vapor-phase soldering fluxes (6) formation of dibutyl decalins (7) fluorination of alkynes (8) synthesis of unsaturated or partially fluorinated compounds (9—11) and conversion of aromatic compounds to perfluorocycHc compounds (see Fluorine compounds, organic). CoF rarely causes polymerization of hydrocarbons. CoF is also used for the conversion of metal oxides to higher valency metal fluorides, eg, in the assay of uranium ore (12). It is also used in the manufacture of nitrogen fluoride, NF, from ammonia (13). 

After venting of the elongated bubble, the region of liquid droplets begins. The vapor phase occupies most of the channel core. The distinctive feature of this region is the periodic dryout and wetting phenomenon. The duration of the two-phase period, i.e., the presence of a vapor phase and micro-droplet clusters on the heated wall, affects the wall temperature and heat transfer in micro-channels. As the heat flux increases, while other experimental conditions remain unchanged, the duration of the two-phase period decreases, and CHF is closer. 

Bowers and Mudawar (1994a) performed an experimental smdy of boiling flow within mini-channel (2.54 mm) and micro-channel d = 510 pm) heat sink and demonstrated that high values of heat flux can be achieved. Bowers and Mudawar (1994b) also modeled the pressure drop in the micro-channels and minichannels, using the Collier (1981) and Wallis (1969) homogenous equilibrium model, which assumes the liquid and vapor phases form a homogenous mixture with equal and uniform velocity, and properties were assumed to be uniform within each phase. 

It is an empirical fact that in the absence of a significant exchange Of solvent flux with the vapor phase the position of the solvent front with respect to time is adequately represented by... 

The primary methodologies for forming thin-film materials with atomic level control are molecular beam epitaxy (MBE) [4-9], vapor phase epitaxy (VPE) [10-12], and a number of derivative vacuum based techniques [13]. These methods depend on controlling the flux of reactants and the temperature of the substrate and reactants. 

Independent of the CVD system, certain constants must be adhered to. The precursor is one of the most important components of the CVD system and is often referred to as the source. The first step in the CVD process is vaporization of the precursor, if it does not already exist as a gas at ambient conditions. The precursor should have sufficient vapor pressure, at least 100 mtorr at delivery temperature, to achieve reasonable deposition rates (16). Ambient temperature liquids are preferred to solids, since it is easier to maintain a constant flux of the precursor in the vapor phase. This is due to the fact that liquids rapidly reestablish equilibrium upon removal of vapors,... 

The synthesis of chalcogenides such as those of the rare earth elements has traditionally been performed through the reaction of rare earth metals or oxides with a molten or vaporous chalcogen source in a high-temperature environment. Soft synthetic methods utilizing lower temperature conditions, such as hydrothermal or flux syntheses, can allow access also to thermodynamically metastable phases. Flux syntheses of R chalcogenides via an alkali poly-chalcogenide flux have been shown to be extremely versatile for the preparation of many new structures, some of which cannot be obtained by direct synthesis from the elements. 

Chemical equilibrium corresponds to zero water flux and uniform chemical potential of water in the membrane interior and in the external vapor phase. 

Crystals grow from their supersaturated vapor by the addition of vapor atoms at their free surfaces. In this process, the surface is subjected to an effective pressure due to the difference in free energy between the solid and vapor. The interface moves outward toward the vapor as it acts as a sink for the incoming flux of atoms. The mechanism by which atoms leave the vapor phase and eventually become permanently incorporated in the crystal is often relatively complex, and the kinetics of the process depends upon the type of surface involved (i.e., singular, vicinal,... 

The diffusion potential of an atom at the surface is proportional to local surface curvature as demonstrated in Section 3.4. The curvature can be determined from Eq. 14.1 and is a function of x. The local diffusion potential produces boundary conditions for diffusion through the bulk or transport via the vapor phase. For surface diffusion, gradients in the diffusion potential produce fluxes along the surface. 

Crystal growth from the vapor phase has been treated in Chapter 12. An expression for the net atom flux, Jv, gained at a macroscopically flat crystal surface during growth from the vapor has been obtained in Exercise 12.2 in the form of Eq. 12.27. To treat surfaces possessing nonuniform curvature, this relationship can be generalized in the form... 

---