Nitrogen thermometry

The wavelength of fhe Stokes laser depends on the species to be probed with the CARS system. For nitrogen thermometry, a rhodamine dye laser is used that produces laser energy at about 607 nm and the CARS or anti-Stokes wavelength is 473 nm. Table 13.1 lists the Stokes and anti-Stokes wavelengths for species of infer-esf in air breafhing combustion assuming a 532 nm pump laser. 

Temperature information from CARS spectra derives from spectral shapes either of the 2-branches or of the pure rotational CARS spectra of the molecular constituents. In combustion research it is most common to perform thermometry from nitrogen since it is the dominant constituent and present everywhere in large concentration despite the extent of chemical reaction. The 2-branch of nitrogen changes its shape due to the increased contribution of higher rotational levels which become more populated when the temperature increases. Figure 6.1-21 displays a calculated temperature dependence of the N2 CARS spectrum for experimental parameters typically used in CARS thermometry (Hall and Eckbreth, 1984). Note that the wavenumber scale corresponds to the absolute wavenumber value for the 2320 cm 2-branch of N2 when excited with the frequency doubled Nd.YAG laser at 532 nm ( 18796 cm ), i. e. = 18796 -1- 2320 = 21116 cm. The bands lower than about 21100 cm are due to the rotational structure of the first vibrational hot band. 

Day, Sosman and Allen, High Temperature Gas Thermometry, Carnegie Inst. Pub. No. 157, 1911. Nitrogen thermometer to 1,550°C. and discussion of fixed temperature points from zinc to platinum. 

Even though the combined production of cryogenic nitrogen and oxygen exceeds the production of any other chemical in the United States, the cryogenic industry does not appear to warrant a separate product line of instruments for diagnostic and control purposes. Low-temperature thermometry is the one exception. The general approach... 

The main trouble with SpRS thermometry is associated with the small Raman cross section. This fact is partly counterbalanced by choosing the SpRS spectrum of the most abundant and stable species. Usually, nitrogen is the best candidate in air-fed combustion realized in laboratory burners [7,9] and the choice proves to be valid even for industrial flames and furnaces [18-20], but this is not enough to make SpRS thermometry evolve into a common resource. For instance, the RS cross section is about three orders of magnitude greater and two-dimensional thermometry is dominated by RS instead of the more accurate SpRS. 

Furuno, S., Akihama, K., Hanabusa, M., Iguchi, S., and Inoue, T. "Nitrogen CARS Thermometry for a Study of Temperature Rrofiles Through Flame Fronts." Combustion... 

Temperature information from CARS spectra derives from spectral shapes either of the Q-branches or of the pure rotational CARS spectra of the molecular constituents. In combustion research it is most common to perform thermometry from nitrogen since it is the dominant constituent and present everywhere in large concentration despite the extent... 

THERMOMETRY. Twelve matched 2 Allen-Bradley carbon-composition resistors were installed on 5% in. centers on a thin-walled stainless steel tube in one of our 6000-liter supply dewars. The objective of this was measurement of gas and possibly liquid temperatures in order to obtain a better idea on pressurization gas requirements, and the amount of heat transferred to the liquid. The resistors were selected to match at room temperature (33 ohms) and in liquid nitrogen (40 ohms). They remained matched in liquid hydrogen(70 ohms). Within our accuracy requirements their resistance R(T) is described by the simple inverse temperature law... 

Answer by Author The carbon resistors used for thermometry and only incidentally for level indication were not treated in any special way. They were selected from a large batch of resistors to match at room temperature and in liquid nitrogen. In the selection process they were subjected to several quick cooling and warming cycles, i.e., they were dunked in an open dewar with liquid nitrogen and then warmed to room temperature in perhaps 3 min. 

Since we were primarily interested in thermometry, we are using a constant-current circuit. The resistors are continuously energized and are made to draw 0.8 ma each in liquid nitrogen and 0.2 ma each in liquid hydrogen. This gives approximately full-scale response on the recorder. Current is changed by changing from a 6-v dry cell battery to a 1.5-v battery. 

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