Diffusivity factors influencing

Airborne contaminant movement in the building depends upon the type of heat and contaminant sources, which can be classified as (1) buoyant (e.g., heat) sources, (2) nonbuoyant (diffusion) sources, and (d) dynamic sources.- With the first type of sources, contaminants move in the space primarily due to the heat energy as buoyant plumes over the heated surfaces. The second type of sources is characterized by cimtaminant diffusion in the room in all directions due to the concentration gradient in all directions (e.g., in the case of emission from painted surfaces). The emission rare in this case is significantly affected by the intensity of the ambient air turbulence and air velocity, dhe third type of sources is characterized by contaminant movement in the space with an air jet (e.g., linear jet over the tank with a push-pull ventilation), or particle flow (e.g., from a grinding wheel). In some cases, the above factors influencing contaminant distribution in the room are combined. 

Graphical interpretation of the factors influencing the critical distance from air supply to the linear obstacle with a height for air supply through a slot diffuser with height Ioq and for air supply through a round nozzle with outlet diameter are presented in Fig. 7.43. Nonisothermal flow has an influence on... 

In addition, it was concluded that the liquid-phase diffusion coefficient is the major factor influencing the value of the mass-transfer coefficient per unit area. Inasmuch as agitators operate poorly in gas-liquid dispersions, it is impractical to induce turbulence by mechanical means that exceeds gravitational forces. They conclude, therefore, that heat- and mass-transfer coefficients per unit area in gas dispersions are almost completely unaffected by the mechanical power dissipated in the system. Consequently, the total mass-transfer rate in agitated gas-liquid contacting is changed almost entirely in accordance with the interfacial area—a function of the power input. 

Important factors influencing the analyte volatilisation process are related to diffusion, porosity, and surface area (for solids). To obtain reproducible results it is necessary to control storage temperature and time strictly. The temperature of the sample is very important because of the specific boiling points of the various analytes. The partition coefficient, K, at equilibrium, is... 

Table 2.1 Factors Influencing Rate of Diffusion of a Substance...

Figure 1. Schematic illustration of factors influencing the production and migration of radon in soils and into buildings. Geochemical processes affect the radium concentration in the soil. The emanating fraction is principally dependent upon soil moisture (1 0) and the size distribution of the soil grains (d). Diffusion of radon through the soil is affected primarily by soil porosity ( ) and moisture content, while convective flow of radon-bearing soil gas depends mainly upon the air permeability (k) of the soil and the pressure gradient (VP) established by the building.

It has been demonstrated that transport rate and selectivity may be modelled using the basic concepts of Fick s law of diffusion (Behr, Kirch Lehn, 1985). Analyses of this type allow a greater appreciation of the interplay of factors influencing such membrane transport phenomena, and enable a clear theoretical differentiation between diffusion-limited and complexation rate-limited cases. 

Intermetallic compound formation may be observed as the result from the diffusion across an interface between the two solids. The transient formation of a liquid phase may aid the synthesis and densification processes. A further aid to the reaction speed and completeness may come from the non-negligible volatility of the component(s). An important factor influencing the feasibility of the reactions between mixed powders is represented by the heat of formation of the desired alloy the reaction will be easier if it is more exothermic. Heat must generally be supplied to start the reaction but then an exothermic reaction can become self-sustaining. Such reactions are also known as combustion synthesis, reactive synthesis, self-propagating high-temperature synthesis. 

To reveal factors which influence activities of acid-base catalysts in alkylation and isomerization is the challenge to activity in this field. Q he greatest amount of work has been done in connection with the effect of para-selectivity, which is observed in alkylation of aromatic hydrocarbons on ZSM-5 type zeolites [1]. This effect has been explained by a number of authors either by the influence of diffusion factors [2,3] or by the isomerizing activity of the external surface of zeolite crystals [4]. In refs. [5,6] and especially in ref.[7] the para-selective effect of ZSM-5 type zeolites is shown to be due to decreasing their isomerizing activity becaiase of the decrease in the concentration of strong protic centres as a result of modifiers introduced. Para-selective effect is related to the action of chemical factors. However, in... 

An edible film should have good water vapor barrier properties (low or no water permeation and diffusion through film), which should not increase or increase very little with increasing relative vapor pressure (Lawton, 1996). Films should withstand mechanical stress and strain to such an extent that they do not break easily under a decent mechanical force (Talja et al, 2008). Thus, composition of starch-based films is an important factor influencing its barrier and mechanical properties. Also, starch-based edible films may have an impact on the sensory and textural characteristics of the food. 

Several factors influence TGA data. Sample size and shape affect the rate and efficiency of decomposition. Powdered versus solid bulk samples will have different decomposition profiles due to the differing surface areas from which exiting decomposition products can leave the sample and be registered as mass losses. Similarly, the packing of the sample in the pan must be even and reproducible from run to run. Loosely distributed particles will heat more evenly and evolve volatilized products more evenly than mounded or densely packed samples. This can be especially important when looking at determinations of residual solvents, moisture or diffusion controlled losses such as plasticizer in the samples. 

The factors influencing selective transport may be divided into internal ones arising from the carrier, and external ones due to the medium. In a diffusion controlled process the rates will depend on the thermodynamic equilibria at the interfaces, i.e., on the relative extraction efficiency towards different substrates. 

Leaf gas exchange rates are highly dependent on local climatic factors influencing C02 diffusion and evaporation rates, especially temperature lapse rates. The dependency of gas-exchange parameters on local climatic factors and leaf anatomy may account for the wide variability in leaf stomatal responses and stable isotope composition over elevation transects found in different species and different regions. 

A further factor influencing dermatopharmacokinetics is the duration of tape stripping procedure. Redistribution of the solute in the SC may occur when tape stripping procedure is performed over a long period of time relative to its lag time for diffusion across SC.15 Furthermore, lateral spreading of the solute from neighboring, noninvolved skin into the stripped area may happen under certain circumstances.16... 

The second application concerned aspects of UHV technology. In UHV systems at equilibrium, the predominant gas load arises from the outgassing of internal surfaces. The factors influencing outgassing, including adsorption/desorption, were discussed (Examples 6.10-6.12). Outgassing from the interior of materials (diffusive outgassing), which can arise with both metallic- and non-metallic materials exposed to vacuum, was quantified in Examples 6.13-6.15. 

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