Oxygen, absorption coefficient

Inspection of the table shows that the quotient a/Wj e is in fact nearly constant that I changes much less rapidly than W e] and that the critical depth has doubled when the highest oxide is reached. All three conditions are reflections of the (positive) absorption effect that occurs in this binary system when iron is replaced by oxygen, which has a lower mass absorption coefficient. 

Yoshida and Akita (Yl) determined volumetric mass-transfer coefficients for the absorption of oxygen by aqueous sodium sulfite solutions in counter-current-ffow bubble-columns. Columns of various diameters (from 7.7 to 60.0 cm) and liquid heights (from 90 to 350 cm) were used in order to examine the effects of equipment size. The volumetric absorption coefficient reportedly increases with increasing gas velocity over the entire range investigated (up to approximately 30 cm/sec nominal velocity), and with increasing column diameter, but is independent of liquid height. These observations are somewhat at variance with those of other workers. 

Mass absorption increases strongly with the atomic number Z. For the 14.4 keV radiation of Fe, the coefficient follows approximately the relation k. 0.003 from oxygen to krypton. Therefore, organic solvents containing sulfur or chlorine are virtually opaque to the Mossbauer radiation. The sulfur component of a 2 mm layer of dimethylsulfoxide (DMSO) absorbs 70% of the Mossbauer radiation (/ = 1.1 g cm ) [35]. Even worse is dichloromethane (CH2CI2), having an absorption coefficient of 16.83 cm g. A layer of 0.1 g cm , which is only 0.75 mm thick (p = 1.33 g cm ), absorbs about 82% of 14.4 keV radiation. For the same reason, chlorinated polymers (PVC) or glass should not be used for... 

Table I. Photoelectric Mass Absorption Coefficients of Halogen Atoms and of Carbon, Oxygen, Hydrogen at 8.34 A (A1 Kali2 emission line) and 13.34 A (Cu Lai. o emission line) (6)...

Because Si — Ti absorption has a very small molar absorption coefficient, we would expect (because of the inverse relation between 8 and T0) the Ti state to have a much greater luminescent lifetime than the same molecules in the Si state. As a result of this longer lifetime, the Ti state is particularly susceptible to quenching, such that phosphorescence in fluid solution is not readily observed as the Ti state is quenched before emission can occur. This quenching in solution involves the diffusion together of either two Ti molecules or the Ti molecule and a dissolved oxygen molecule or some impurity molecule. In order to observe phosphorescence it is necessary to reduce or prevent the diffusion processes. The techniques most often used are ... 

The relations of molar extinction coefficients and oxygen absorption rates, plotted vs. time, are illustrated in Figures 3 and 4 (solvents, benzene and butyric acid, respectively). The variation of coefficients was parallel to the rate of oxygen absorption—i.e. the larger the coefficient, the higher the oxygen absorption rate. It is considered therefore that the catalyst at its maximum absorption coefficient is in a desirable form for oxidizing acrolein. 

Thus, when deahng with gas transfer in aerobic fermentors, it is important to consider only the resistance at the gas-liquid interface, usually at the surface of gas bubbles. As the solubihty of oxygen in water is relatively low (cf. Section 6.2 and Table 6.1), we can neglect the gas-phase resistance when dealing with oxygen absorption into the aqueous media, and consider only the liquid film mass transfer coefficient Aj and the volumetric coefficient k a, which are practically equal to and K a, respectively. Although carbon dioxide is considerably more soluble in water than oxygen, we can also consider that the liquid film resistance will control the rate of carbon dioxide desorption from the aqueous media. 

The volumetric coefficient A a for oxygen absorption into oil-in-water emulsions is of interest in connection with fermentation using hydrocarbon substrates. Experimental results [7] have shown that such emulsions can be categorized... 

The value of the liquid phase mass transfer coefficient can be obtained from the experimental data for physical absorption of oxygen into blood saturated with oxygen, or estimated from the data with the same apparatus for physical oxygen absorption into water or a reference liquid or solution with known physical properties. Mass transfer coefficients for liquids flowing through or across tubes or hollow fibers can usually be correlated by equations, such as Equation 6.26a for... 

In a hollow-fiber-type membrane blood oxygenator, the blood flows outside and across the hollow fibers. The total membrane area (outside fibers) is 4 m . From the data on physical oxygen absorption into water at 20 °C, the following empirical equation (a) for the water-phase oxygen transfer coefficient (cm min ) in this particular oxygenator at 20 °C was obtained. 

Early work. In 1885, Janssen found that in oxygen at pressures of tens or hundreds of atmospheres new absorption bands occur which are unknown from absorption studies at atmospheric pressures see pp. 357ff. for details. The associated absorption coefficients increase as the square of density, in violation of Beer s law. The observed quadratic dependence suggests an absorption by pairs of molecules Beer s law, by contrast, attempts to describe absorption by individual molecules. 

Fig. 2. Absorption spectrum of oxygen in the Schumann-Runge band system. The absorption coefficient, k, is defined by the equation I = la exp ( — kx), where h and I are the incident and transmitted light intensities and x is the layer thickness of the absorbing gas reduced to STP. This figure is taken from ref. (101) with the permission of The Journal of Chemical Physics.

The most recent measurements of the absorption coefficients of oxygen have been made by Watanabe et al. (101). For the transition 32u- -32 absorption intensities in the Schumann-Runge bands are shown in Figure 2 and in the Schumann-Runge continuum in Figure 3. 

Akita and Yoshida (1974) evaluated the liquid-phase mass-transfer coefficient based on the oxygen absorption into several liquids of different physical properties using bubble columns without mechanical agitation. Their correlation for kL is... 

Since the oxygen is sparingly soluble gas, the overall mass-transfer coefficient KL is equal to the individual mass-transfer coefficient KL. Our objective in fermenter design is to maximize the oxygen transfer rate with the minimum power consumption necessary to agitate the fluid, and also minimum air flow rate. To maximize the oxygen absorption rate, we have to maximize KL, a, C - CL. However, the concentration difference is quite limited for us to control because the value of C L is limited by its very low maximum solubility. Therefore, the main parameters of interest in design are the mass-transfer coefficient and the mterfacial area. 

The overall volumetric mass transfer coefficients measured by pure oxygen absorption were expressed as a function of the total specific power dissipated in the liquid as follows ... 

Fig. 4. Liquid film mass transfer coefficient measured by pure oxygen absorption vs. total power dissipated in the liquid, e. Symbols and lines (see Table 1).

L liquid-side mass transfer coefficient measured by oxygen absorption, ms-1... 

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