Mixture-fraction measurements

One of the most challenging aspects of modeling turbulent combustion is the accurate prediction of finite-rate chemistry effects. In highly turbulent flames, the local transport rates for the removal of combustion radicals and heat may be comparable to or larger than the production rates of radicals and heat from combustion reactions. As a result, the chemistry cannot keep up with the transport and the flame is quenched. To illustrate these finite-rate chemistry effects, we compare temperature measurements in two piloted, partially premixed CH4/air (1/3 by vol.) jet flames with different turbulence levels. Figure 7.2.4 shows scatter plots of temperature as a function of mixture fraction for a fully burning flame (Flame C) and a flame with significant local extinction (Flame F) at a downstream location of xld = 15 [16]. These scatter plots provide a qualitative indication of the probability of local extinction, which is characterized... 

Figure 7.2.12 shows scatter plots of instantaneous measurements of temperature and CH4 mole fraction obtained at a height of 5 mm and at several radial locations, which are color-coded in the figure. The foremost observable characteristics are that there are no samples richer than 0.2 in the mixture fraction (1.0 being pure fuel) and that many samples remain at room temperature even within the limits of flammability. Many... 

Note that when solving the CFD transport equations, the mean velocity and turbulence state variables can be found independently from the mixture-fraction state variables. Likewise, when validating the CFD model predictions, the velocity and turbulence predictions can be measured in separate experiments (e.g., using particle-image velocimetry [PIV]) from the scalar field (e.g., using planar laser-induced fluorescence [PLIF]). 

Other measurements such as gas species and soot all have importance in fire plumes but will not be discussed here. As we have seen for simple diffusion flames, the mixture fraction plays a role in generalizing these spatial distributions. Thus, if the mixture fraction is determined for the flow field, the prospect of establishing the primary species concentration profiles is possible. 

Methane-air diffusion flames are selected for the example to be studied here. The temperature T and species mass fractions Yi (for species i) in such flames are functions of the mixture fraction Z, which varies from zero in air to unity in fuel and measures the fraction of the material present that came from the fuel. Figure 25.2 is a schematic illustration of major profiles in the methane-air diffusion flame as functions of Z, obtained by the rate-ratio as3miptotics described above. The work to be reported here adds to this picture the chemistry relevant to the production of oxides of nitrogen. 

The surface tension of the aqueous solution of dode-cylaitunonium chloride (DAC) — decylairanonium chloride (DeAC) mixture was measured as a function of the total molality m of surfactants and the mole fraction X of DeAC in the total surfactant in the neighborhood of the critical micelle concentration (CMC). By use of the thermodynamic equations derived previously, the mole fraction in the mixed adsorbed film was evaluated from the y vs. X and m vs. X curves. Further, the mole fraction in the mixed micelle was evaluated from the CMC vs. X curve. By comparing these values at the CMC, it was concluded that the behavior of DAC and DeAC molecules in the mixed micelle is fairly similar to that in the mixed adsorbed film. 

The surface tension y of the aqueous solution of dodecylammonium chloride — decylammonium chloride mixture was measured as a function of m at a given value of the mole fraction X of DeAC at 298.15 K under atmospheric pressure. The results are shown in Figure 1. It is seen that the y vs. m curves are similar in appearance. This behavior is in harmony with that observed previously in a low concentration range (9). Moreover, the formation of micelle is found to cause the curves to break sharply at the CMC which increases with X. It should be noted, however, that the y vs. m curve of a mixture has a very shallow minimum in the immediate vicinity of the CMC. 

FIGURE 2-17 The titration curve of acetic acid. After addition of each increment of NaOH to the acetic acid solution, the pH of the mixture is measured. This value is plotted against the amount of NaOH expressed as a fraction of the total NaOH required to convert all the acetic acid to its deprotonated form, acetate. The points so obtained yield the titration curve. Shown in the boxes are the predominant ionic forms at the points designated. At the midpoint of the titration, the concentrations of the proton donor and proton acceptor are equal, and the pH is numerically equal to the pAfa. The shaded zone is the useful region of buffering power, generally between 10% and 90% titration of the weak acid. 

Al any methods used to study protein interactions and proteolysis in - - complex mixtures are often unsuitable for application to food systems, where severe heat treatments or enzymic modification may change the properties of proteins and their reactivity in an analytical procedure. Chromatographic, electrophoretic, and immunochemical methods are excellent tools for fractionating protein mixtures and measuring the concentrations of the individual components, but heat treatment or enzymic... 

The typical approach taken when attempting to vary the concentration of intermolecular modes is the use of binary mixtures. When one considers the many body nature of the intermolecular modes and the complexity of binary mixtures, it is not directly evident that there is any proportionality between the ill-defined concept of concentration for intermolecular modes and the binary mixture fraction. An additional complication in the use of binary mixtures comes from the significant changes in the polarizability weighted density of states as a function of binary mixture fraction. In other words, the intermolecular spectrum is changing with binary mixture fraction. These types of effects are clearly evident in third-order measurements of CS2 in binary mixtures (3). 

Situations with an excess of ion exchanger occur if,. for example, a given ionic species has to be removed from the solution by a batch operation. An excess of particles with ion exchange properties is usually also present when the sorption of trace ions by soils or soil components (clay minerals, oxides, humic substances) is investigated. Especially in this latter case the particles will be invariably polydisperse. This anomalous kinetic behavior will, of course, only be observed experimentally if the concentration of ions A in the solution and in the various fractions of the ion-ex-changer particles in the mixture are measured continuously. 

Another method suggested by the authors for predicting the solubility of gases and large molecules such as the proteins, drugs and other biomolecules in a mixed solvent is based on the Kirkwood-Buff theory of solutions [18]. This theory connects the macroscopic properties of solutions, such as the isothermal compressibility, the derivatives of the chemical potentials with respect to the concentration and the partial molar volumes to their microscopic characteristics in the form of spatial integrals involving the radial distribution function. This theory allowed one to extract some microscopic characteristics of mixtures from measurable thermodynamic quantities. The present authors employed the Kirkwood-Buff theory of solution to obtain expressions for the derivatives of the activity coefficients in ternary [19] and multicomponent [20] mixtures with respect to the mole fractions. These expressions for the derivatives of the activity coefficients were used to predict the solubilities of various solutes in aqueous mixed solvents, namely ... 

Conductometry is an electrochemical technique used to determine the quantity of an analyte present in a mixture by measurement of its effect on the electrical conductivity of the mixture. It is the measure of the ability of ions in solution to carry current under the influence of a potential difference. In a conductometric cell, potential is applied between two inert metal electrodes. An alternating potential with a frequency between 100 and 3000 Hz is used to prevent polarization of the electrodes. A decrease in solution resistance results in an increase in conductance and more current is passed between the electrodes. The resulting current flow is also alternating. The current is directly proportional to solution conductance. Conductance is considered the inverse of resistance and may be expressed in units of ohm (siemens). In clinical analysis, conductometry is frequently used for the measurement of the volume fraction of erythrocytes in whole blood (hematocrit) and as the transduction mechanism for some biosensors. 

Despite all difficulties mentioned above, examples for C02 containing microemulsion stabilised by a technical grade non-ionic surfactant have been found (see Fig. 11.3 in Chapter 11). The studied system consists ofwater/NaCl- -propane/C02-Lutensol XL70 with varying amounts of C02 in n-propane/C02 mixtures. All measurements were carried out at p = 220 bar and at equal volume fractions of the two solvents [56], The respective phase diagrams have been studied as a function ofthe temperature T and the total surfactant... 

Witt [1959] studied under vacuum gamma-radi-ation-induced crosslinking in butadiene-styrene copolymers, homopolymers and mixtures of these homopolymers, (Table 11.9). The behavior of the styrene units in the copolymers and in the physical mixtures, was different. Gel fraction measurements showed that in the copolymer, the styrene units did inhibit the crosslinking of the polybutadiene. However, there was no evidence of such inhibition in the mill- and latex-prepared physical mixtures of the two homopolymers. 

Controlling the internal vapor flow to the section above the side draw Reboiler heat duty is measured and divided by the latent heat of the boiling mixture the measured side product flow is subtracted from the quotient to give the internal vapor rate in the section above the side draw. In a steam (or condensing vapor) reboiler, the internal vapor rate is computed as a constant times the measured steam rate less the measured side product flow, with the constant equal to the ratio of the latent heat of steam to that of the boiling mixture. An internal vapor controller (IVC) uses this computed internal vapor to manipulate product flow (Fig. 19.76). A limitation of this technique is that internal vapor is computed as a small difference between two large numbers and can therefore be in error. The error escalates as the internal vapor rate becomes a smaller fraction of the total vapor traffic below the side draw. 

Device not calibrated - recalibrate. Calibration curve deviates from linearity at high mass fractions - measure against known standard. Impurities in the stream - analyze a sample. Mixture is not all liquid - check sample. Calibration data are temperature dependent - check calibration at various temperatures. System is not at steady state - take more measurements. Scatter in data - take more measurements. 

To be able to select a crystallization temperature in the single liquid phase region at a given amine fraction, the liquid-liquid equilibrium lines of the amine-water-NaClsat systems were determined. To establish to what extent an antisolvent reduces the sodium chloride solubility and to calculate the maximum obtainable magma densities during crystallization, sodium chloride solubilities in the amine-water mixtures were measured. Finally continuous crystallization experiments were carried out and the feasibility of an antisolvent recovery by a temperature increase was investigated. 

The whole procedure of the human blood-cell suspension study is presented schematically in Fig. 50. The TDS measurements on the cell suspension, the volume-fraction measurement of this suspension, and measurements of cell radius are excecuted during each experiment on the sample. The electrode-polarization correction (see Sec. II) is performed at flie stage of data treatment (in the time domain) and then the suspension spectrum is obtained. The singlecell spectrum is calculated by the Maxwell-Wagner mixture formula [Eq. (88)], using the measured cell radius and volume fraction. This spectrum is then fitted to the single-shell model [Eq. (89)] in the case of erythrocytes or to the double-shell model [Eqs (94)-(98)] to obtain flie cell-phase parameters of lymphocytes. 

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