Diffusion activation energy, total

It appears that the rate constant for most of the boards has a smaller temperature dependence than the initial maximum rate, the corresponding "activation energy" E3 being around or less than 5 kcal/mol. An important conclusion is that the rate is diffusion limited. This has to be compared to a mean activation energy around 20 kcal/mole for the initial maximum rate of heat release for the commercial boards. As a consequence thereof the total heat release extrapolated over infinite time does increase to a significant extent with temperature from 150 to 230°C. 

Concentration of A Arrhenius constants Arrhenius constant Constant in equation 5.82 Surface area per unit volume Parameter in equation 5.218 Cross-sectional area Concentration of B Stoichiometric constants Parameter in equation 5.218 Concentration of gas in liquid phase Saturation concentration of gas in liquid Concentration of G-mass Concentration of D-mass Dilution rate DamkOhler number Critical dilution rate for wash-out Effective diffusion coefficient Dilution rate for maximum biomass production Dilution rate for CSTF 1 Dilution rate for CSTF 2 Activation energy Enzyme concentration Concentration of active enzyme Active enzyme concentration at time t Initial active enzyme concentration Concentration of inactive enzyme Total enzyme concentration Concentration of enzyme-substrate complex with substance A... 

In this equation, if the rate of diffusion is faster than that of the catalytic reaction at the surface (ko kc), the Arrhenius plot of rr gives the apparent activation energy Ec of kc. This is the reaction-controlled condition. On the other hand, if the rate of the catalytic reaction is faster than that of diffusion (kc 2> kid, the Arrhenius plot of rr gives the characteristics of temperature dependence of ko. This is the diffusion-controlled condition. Under diffusion-controlled conditions, the transferred reactant decreases at once at the surface (Cs = 0) because of the fast catalytic reaction rate. The gas flow along the catalyst surface forms a boundary layer above the surface, and gas molecules diffuse due to the concentration gradient inside the layer in the thickness direction. As the total reaction... 

By definition, the rate at which the tracer atom is displaced by a surface vacancy is the product of the vacancy density at the site next to the tracer times the rate at which vacancies exchange with the tracer atom. For the case where the interaction between the tracer atom and the vacancy is negligible, the activation energy obtained from the temperature dependence of the total displacement rate equals the sum of the vacancy formation energy EF and the vacancy diffusion barrier ED. When the measurements are performed with finite temporal resolution and if there is an interaction present between the vacancy and the indium atom, this simple picture changes. 

The authors of Ref. generalized all the published polymer combustion limits from the viewpoint of the effect of different factors on the cooling of the reaction zone. At the extinction limit of diffusion combustion, the ratio of heat losses from the front edge of the combustion zone to the total heat generation due to the chemical reaction must be proportional to RT, /E here, Tj is the flame temperature at the extinction limit and E the gas-phase reaction activation energy... 

D Effective Diffusivity of Porous Preform Effective Ordinary Binary Diffusivity Reactant Knudsen Diffusivity D = v dl3) Deposition Reaction Activation Energy / Reactive Species Mole Eraction Kn Knudsen Number (Kn = m Reactive Species Molecular Weight N Avogadro Number p Total Gas Pressure... 

The functional form of the triggers ate based on transition state, as determined by the quantum mechanical calculation and their numerical values are parameterized to satisfy the macroscopically determined rate constant and activation energy. Local equilibration at the end of the reaction helps in maintaining the correct heat of reaction and structure. For the vahdation of the algorithm, it has been implemented to study proton transport in bulk water. In bulk water the two components of the total diffusivity were found to be uncorrelated. 

TG signal, the activation energy of Dr should be totally different from that of Dp because of the activation energy of the reaction.) Further, we find that the small but non-negligible difference in Ed between the radical and the parent molecules can be explained by the concept of the larger volume of the radical, which supports the our radical diffusion model. 

One would physically expect that as pressure increases the solid surface may get smoother due to the filling of small pores and cavities with adsorbed molecules, and as a result the reflection time of gas phase molecules from the surface may become shorter. The values of / in Table 1 are close to unity as expected and they are in an increasing order of n-hexane, carbon tetrachloride and benzene. On the other hand, the parameter a for n-hexane is much higher than that of the others. Since the parameter a in Eq. 3 represents how fast the Knudsen diffiisivity increases with pressure, one would expect a substantial contribution of the Knudsen diffusion for n-hexane to the total permeability at very low pressures. Also the parameter is a measure of how fast the activation energy for surface diffusion decreases with adsorbed concentration. As Table 1 indicates, the surface diffusion permeabilities of n-hexane and carbon tetrachloride are expected to increase more sharply than that of benzene. 

The Knudsen diffusion, viscous flow and surface diffiision for strongly adsorbing vapors are well described at low range of pressures in this paper. The collision-reflection flictor for Knudsen diffusion is found to be not constant but exhibit a modest increase with an increase in pressure. The dependence of the Knudsen diflusion for n-hexane on pressure is stronger than that of the other vapors. Moreover the activation energy for the surflice diffiision of ra-hexane exhibits a faster decreasing behavior in comparison with the others. Conclusively, the reason for the minimum appearance in the total permeability of ra-hexane can be attributed by the interplay between the Knudsen diflusion and surface diffusion. 

Current/Voltage Relationships for Irreversible Reactions Many voltammetric electrode processes, particularly those associated with organic systems, are partially or totally irreversible, which leads to drawn-out and less well defined waves. The quantitative description of such waves requires an additional term (involving the activation energy of the reaction) in Equation 23-11 to account for the kinetics of the electrode process. Although half-wave potentials for irreversible reactions ordinarily show some dependence on concentration, diffusion currents are usually still linearly related to concentration many irreversible processes can, therefore, be adapted to quantitative analysis. 

Generally an Arrhenius (exponential) type of relation represents the diffusion coefficient as a fimction of the temperature, with AQa the activation energy of diffusion. Similarly the parameters b and K (9.16) can be expressed with Arrhenius functions with Qa the (isosteric) heat of adsorption. Consequently is also activated with a total apparent activation energy of (Qa AQa). For chemisorption AQa has about the same value as Qa [1]. For physical adsorption the value of AQa is < (0.5-0.66)Qa. Since the surface flux is small at very low temperature as well as very high temperature there must be a maximum. The possibility of observing this maximum depends on the relative magnitudes of Qa and AQa-... 

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