Exchange flux density

For simplicity we drop the tilde used in Section VI.2.) The comparison with Eq. (106) shows that A is identical with the exchange flux density... 

In the expressions for the gas exchange coefficient employed previously, it is evident that the air-water gas exchange flux density is proportional to the difference between a chemical concentration in the water (Cw) and the corresponding equilibrium concentration (Cw H) in air. Consequently, the difference between actual and equilibrium concentration in the water tends to decay exponentially, as expected for any first-order process. In many situations, exponential decay may provide a useful model of a volatile chemical concentration in a surface water. A classic example is degassing of a dissolved gas from a stream if the gas is present at concentration C0 upstream, atmospheric concentration of the gas is negligible, and flow is steady and uniform along the stream, then the gas concentration in the stream is given by... 

The specific molar exchange flux density between the anode gas channel and the electrode is obtained from the electrode model ... 

The total molar exchange flux density is the sum of the specific exchange fluxes ... 

At equiUbrium the overall reaction takes place forth and back at equal rates ro as a result of thermal energy. The activation process forth and back may not be symmetrical in this case, but that will not affect us at present. Similarly to the random diffusion coefficient connected with these thermal disorders in bulk Dr = 1/6 ro we introduce an exchange coefficient for interfaces k, = roSi which says something about the thermal fluctuations of the reaction across the interface of thickness Si. We can alternatively express this as an exchange flux density... 

Temperature and contaminant gradients along the room height and separation stability between the upper and lower zones are influenced by turbulent exchange between these zones. The heat flux density due to turbulent exchange can be determined as ... 

Fig. 1. Rates of CO2 assimilation, A (/miol s ) leaf conductance, g (mol m s ) intercellular partial pressure of CO2, Pi (Pa) soil water potential and leaf water potential, xp (MPa) during gas-exchange measurements of a 30-day-old cotton plant, plotted against day after watering was withheld. Measurements were made with 2 mmol m sec" photon flux density, 30 °C leaf temperature, and 2.0 kPa vapour pressure difference between leaf and air (S.C. Wong, unpublished data).

Local flux-density profile, 23 816 Localized molecular orbital (LMO) calculations, 10 633 Locally weighted regression, 6 53 Local oscillator (LO), 23 142, 143 Local toxicity, 25 202 Locard Exchange Principle, 12 99 Lochett, W., 11 8... 

The rate at which corrosion occurs is expressed as the current density (A m" ), i.e. the ionic flux across the electrical double layer of the metal and at equilibrium, it is termed the exchange current density. The Tafel equation relates the exchange current density to the charge transfer overpotential. 

When the cathodic current density (jc) is equal to the anodic current density (/a), the net current flowing across the electrode-solution interface is zero, and the net flux of O and R is zero. For this condition, the current densities represent the equilibrium-exchange current density (/0), given by ... 

For convenience, we have been discussing facilitated diffusion into a cell, but the same principles apply for exit and for fluxes at the organelle level. Let us assume that a transporter for K+ exists in the membrane of a certain cell and that it is used as a shuttle for facilitated diffusion. Not only does the carrier lead to an enhanced net flux density toward the side with the lower chemical potential, but also both the unidirectional fluxes and i ut can be increased over the values predicted for ordinary diffusion. This increase in the unidirectional fluxes by a carrier is often called exchange diffusion. In such a case, the molecules are interacting with a membrane component, namely, the carrier hence the Ussing-Teorell equation [Eq. 3.25 = c /(ctjeljFEM/RT)] is not obeyed because it does not consider... 

Table 9-1. Summary of Gas Exchange Parameters and Flux Densities Within a 2-m-Tall Com (Maize, Zea mays) Crop at Noon on a Sunny Daya...

Evaluation of the A9 s that characterize an enclosure involves solution of a system of radiation balances on the surfaces. If the assumption is made that all the zones of the enclosure are gray and emit and reflect diffusely, then the direct-exchange area ij, as evaluated for the black-surface pair A and Ap applies to emission and reflections between them. If at a surface the total leaving-flux density, emitted plus reflected, is denoted by W (and called by some the radiosity and by others the exitance), radiation balances take the form ... 

The amount of Es available at this time was very small about N = 10 atoms (a 4- 10 g). At a flux density of a particles = 10 " cm s , a cross section (Ta n = 1 mb and an irradiation time of 10 s a yield N

single atoms, the recoil technique was applied (Fig. 14.6). Es was electrolytically deposited on a thin gold foil. The recoiling atoms of Md were sampled on a catcher foil. After irradiation, the catcher foil was dissolved and Md was separated on a cation-exchange resin. In 8 experiments 17 atoms of Md were detected and identified by their transmutation into the spontaneously fissioning the properties of which were known ... 

However, the available flux densities often result from several contributions as for example the sum of radiation from a hot wall and exchange with a hot gas. Having in mind that the equation (5) related to this last process represents a minimum (qco can be much higher in the case of high particle Reynolds numbers), the values of q, + qco can approach the limit flux density deflned in this work. In these conditions, we can expect that low char fractions will be formed. 

With the help of these results, a comparison of the performances of pyrolysis reactors can be made on the basis of the types and extents of the elementary heat exchanges processes (radiation, ablation, convection). The calculations show that in some practical cases (ablative pyrolysis and cyclone reactor), it is possible to reach high flux densities and hence avoid the formation of char. 

In the most general case, which must be invoked when the value of the dimensionless Henry s law constant is on the order of 0.01, both resistances contribute to limiting the gas exchange rate. In this case, the complete expression for flux density must be used ... 

The dissolved concentration of trichloroethylene (TCE, C2C13H) in a lake is 1 ppb. Given a dimensionless Henry s law constant, H, of 0.4, and a measured gas exchange coefficient of 3 X 10 cm/sec in water, for propane (C3H8), what is the flux density of TCE from the lake ... 

Accurate estimates of particle deposition are difficult to obtain because of the complexity of natural surfaces and the diversity of atmospheric particles. The long-term deposition of particles on vegetative surfaces often is estimated using a deposition velocity model in which the flux density of particles is calculated as the product of a modeled deposition velocity and a measured concentration of particles in the air (Hicks et al., 1987). A deposition velocity is used in a manner similar to a piston velocity in air-water gas exchange (Section 2.3). In a deposition velocity model, the flux density of atmospheric particles to the surface is... 

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