Temperature line reversal

R J. Senorans, M. Heiraiz and J. Tabera, On-line reversed-phase liquid cliromatography using a programmed temperature vaporizer as interface , 7. High Resolut. Chromatogr. 18 433-437(1995). 

Senorans, R J., Reglero, G., and Herraiz, M., Use of a programmed temperature injector for on-line reversed-phase liquid chromatography-capillary gas chromatography, /. Chromatogr Sci, 33, 446, 1995. 

It is uncertain to what extent thermal equilibria are achieved in different parts of the flames. — A number of procedures are (in principle) available to determine flame temperatures The immediate measurement, for example by thermocouples, the thermochemical calculation, line reversal methods for electronic excitation temperatures, determination of vibrational or rotational temperatures. In addition more recent methods like advanced Raman techniques may be applied. 

Table 7.7 gives some data on flame temperatures obtained by Shimizu for oxidizer/shellac mixtures. Sodium oxalate was added to yield a yellow flame color and permit temperature measurement by the "line reversal" method [11]. 

On pp 289-310 (Ref 21), A.G. Gaydon, Shock-Tube Studies of Processes of Electronic Excitation in Gases reported that the spectrum-line reversal temperature in shock-heated gases can be used to obtain information about efficiencies and processes of electronic excitation of metal atoms at high temperatures. For excitation by molecules, the electronic excitation temperature tends to follow the effective vibrational temperature of the molecules, and reversal temperatures may be low near the shock front if. the vibrational relaxation time is appreciable. Although excitation of metal atoms by cold inert gases has a very small effective cross-section, it is shown that at 2500°K the cross-sections of excitation of Cr or Na by Ar or Ne are around 1/20 of the gas-kinetic cross-sections... 

Various approaches to measuring flame temperature are well described in Gaydon s book on flames (see Appendix C). The best methods are spectroscopic rather than those which use thermocouples. The sodium line reversal method is perhaps the easiest. Sodium is added to the flame and the sodium D lines viewed against a bright continuum source (e g. a hot carbon tube). When the flame is cooler than the source the lines appear dark because of absorption. When the flame is hotter than the tube, the bright lines stand out in emission. The current to the tube, which will have been precalibrated for temperature readings by viewing the tube with an optical pyrometer, is adjusted until the lines cannot be seen. At this reversal point, the flame and tube temperature should be equal. 

Dr. Sharkey Attempts were made to use C H ratio following laser irradiation as an indication of the reaction temperature, as Dr. Linden suggests. Collecting the irradiated coal was difficult, and special techniques are now being devised. Use of a spectrum-line reversal technique is another possibility. 

Figure 4.20 shows the correlation of experimental data of Hammerschmidt (1939) with five inhibitors with the pressure and temperature axes reversed from their normal position. The striking feature of Figure 4.20 is the parallel nature of all experimental lines, for the inhibition effect of both alcohols and salts relative to pure water. The parallel solid lines provide some indication of the molecular nature of the inhibition. Normally a phase transformation is considered relative to the change in Gibbs free energy defined as ... 

Tourin, R.H., Spectroscopic Gas Temperature Measurement, Elsevier Publishing Co., Amsterdam, 1966. Gaydon, A.G. and Wolfhard, H.G., The spectrum-line reversal method of measuring flame temperature, Proc. Phys. Soc. (London), 65A, 19, 1954. 

Temperature Measurements. Sodium line reversal temperature profile measurements were made on the flame series with varying additions of H2S. Results for H2/O2/N2 (3/1/4,5,6) are shown in Figure 3. The increase in temperature with distance above the burner is due to the slow recombination of the radicals H and OH. In the stoichiometric flames the temperature reaches a plateau in a few centimeters above the burner. In the richer flames the temperature gradient is steeper indicating a larger departure of the radical concentration from equilibrium values. The equilibrium temperatures decrease with H2S addition. However, the presence of sulfur compounds enhances radical recombination (6,11) producing almost equivalent temperature profiles, independent of H2S addition. 

Figure 3. Sodium line reversal temperature profiles above the burner surface in...

The present work involves measurement of k in a 0.1 atmosphere, stoichiometric CH -Air flame. All experiments were conducted using 3 inch diameter water-cooled sintered copper burners. Data obtained in our study include (a) temperature profiles obtained by coated miniature thermocouples calibrated by sodium line reversal, (b) NO and composition profiles obtained using molecular beam sampling mass spectrometry and microprobe sampling with chemiluminescent analysis and (c) OH profiles obtained by absorption spectroscopy using an OH resonance lamp. Several flame studies (4) have demonstrated the applicability of partial equilibrium in the post reaction zone of low pressure flames and therefore the (OH) profile can be used to obtain the (0) profile with high accuracy. 

Flame temperature measurements by the sodium line reversal method were made with hydrazine perchlorate strands containing 2% thiourea and 2% sodium chloride. This amount of sodium chloride was necessary to achieve a sufficient intensity of emission of the sodium D-line for these experiments. It may be pointed out that in oxygen-rich, chlorine-containing flames such as this, the concentration of sodium atoms is decreased... 

Thermodynamic calculations for the composition containing 2% thiourea and 2% sodium chloride were made, and the theoretical flame temperature was found to be 2224° K. A series of measurements by the sodium line reversal method gave 2275 50° K. for the flame temperature. This is close enough agreement so that we feel that thermodynamic equilibrium is achieved in the flame, and the reaction products are as written above. This differs markedly from the results with ammonium perchlorate where a substantial fraction of the nitrogen was present as oxides of nitrogen even at elevated pressures (16). 

Line reversal temperatures can be obtained if the hot gas is optically thick in the wavelength of some particular line (P2, P3). With a light source of known temperature (i.e., a calibrated tungsten lamp) placed behind the gas emitting this line, if the gas is hotter than the source it will appear brighter. At the same temperature both blend. 

A recent experiment in a laboratory MHD channel at Stanford ( ) has shown that, under MHD conditions (high potassium loading), the addition of phosphorus, even in amounts much greater than those found in coal, has a much smaller effect on electron concentration and conductivity than would be predicted by the above modeling. That experiment Involved simultaneous measurement of electron concentration by submillimeter interferometry, of positive ion concentration by a swept electric probe, and of plasma temperature by the emission-absorption (line-reversal) technique, made in an ethanol-fueled, potassium-seeded combustion plasma. 

More revealing in relation to the comparative lack of reactivity of nitric oxide are the observations of Wolfhard and Parker on H2 + NO2 flames. Here nitric oxide is found strongly in absorption in the burnt gas of both rich and lean flames, showing that it does not play a major part in the reaction. This conclusion is supported by measurement of the flame temperature of the stoichiometric mixture for H2 + 5NO2 = H2O + 5N2 [286]. Theoretically this should be 2890 K if the stoichiometry is as quoted. The measured flame temperature by line reversal was 1780 K. 

Coincidentally with the revival of atomic absorption methods, renewed interest in flame processes has arisen among many groups of workers (Bl, F7, G3, M5). Absorption techniques including the line reversal apparatus have contributed significantly to our understanding of atomic activation, excitation, atomic population densities, and temperature gradients. At the present time, Ae flame represents the most convenient means to create an atomic vapor under reproducible conditions. For these reasons, a short discussion of processes taking place in the flame is needed. Other means of production of activated atoms will be mentioned under instrumentation and techniques (Section 4.5). 

The temperature were measured by means of the so called line reversal method, where the sodium oxalate was necessary to produce the Na-D lines. 

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