The sun used as a flame temperature standard.

Abstract

view Abstract Citations (1) References Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The sun used as a flame temperature standard. Wilson, Raymond H., Jr. Abstract An investigation of the temperature of the hydrogen-fluorine flame was undertaken by the Research Institute of Temple University as part of the Office of Naval Research Physical Science Division program on extreme temperatures. Theoretical work, based on chemical thermodynamics, indicated a temperature around 5ooo0K. President A. V. Grosse of the Institute suggested an approach to direct measurement of the temperature by the standard sodium spectral line reversal technique with possible interferometric observation of the fine-structure of the lines. This method applies an elementary spectroscopic principle familiar to astronomers by arranging a background continuous radiator of variable effective brightness temperature, which can then be measured with an optical pyrometer at the precise point of line-reversal. This temperature is then that of the intervening gas containing the element whose line was reversed. The background radiation source must be hotter than the flame, and, since no feasible laboratory source higher than 38000K was available, the sun introduced by a heliostat served this purpose for measuring the maximum flame temperature, which turned out to be 43000 ~ 1500K at atmospheric pressure. This use of the sun in place of a laboratory continuous radiator implies man~ considerations of special interest to astronomers. Three such questions are discussed particularly. First, the standard element sodium, introduced into the flame for its reversible lines, could not be freely used when the sun, with its D lines, was used as a background. Hence lithium was chosen for its conspicuous resonance line at 6708 A which is, however, practically absent from the solar spectrum, as shown in spectrophotometric tracings by Greenstein and Richardson.' Another advantage of this line at 6708 A is that the standard optical pyrometer filter band is centered at 6650 A, so that, for such a short interval, the curve of intensity versus wave length can be assumed that of a black-body, a necessary condition for immediate application of calibration tables. A second possible concern to astronomers in thus relying on the sun as a standard is the varying absorption by the earth's atmosphere. This effect is shown to be not harmful, provided it is sensibly constant for the minute or two between an observation of line-reversal and a pyrometer reading of the sun's brightness temperature. In fact, there was found advantage in combining the smog of Philadelphia with decreasing solar altitude to give a brightness temperature only slightly above 43oo0K, so that little additional instrumental absorption was necessary for line- reversal. Finally, there is the limb-darkening of the sun, which causes the sun's brightness temperatures, as viewed from outside the earth's atmosphere, to vary from about 68oo0K to 54000K, from center to limb, respectively. Hence for a flame temperature within the 14000 between these range points (reduced by absorption), and with a diametral slit setting, the reversed part of the line would appear broadest at the sun's center, tapering to points at a limb-distance where flame and solar brightness temperatures were equal. Then the pyrometer could be set precisely at that same limb-distance to give the flame temperature. Photography and further investigation of this effect might prove useful also for purely astronomical purposes. I. Ap. J. 113, 537, 1951. University of Louisville, Louisville, Kentucky. Publication: The Astronomical Journal Pub Date: 1952 DOI: 10.1086/106646 Bibcode: 1952AJ.....57...29W full text sources ADS |