Experimental measurements of the population temperature behind ·:he rebound shock in a shock tube are presented. Previous shock tube measurements of the oscillator strength of the OH 2~-2n band system made in this laboratory(l) have been corrected.
THEORETICAL CONSIDERATIONS
The integrated intensity is in principle calculable and can be expressed in the square of the matrix element for. If the detector response varies significantly above 26.w*, the right-hand side of Eq. 9 must be multiplied by the relative spectral response of the detector at lt. 12) where Kr = K1r/~0Aeff' and ~0 and Aeff are respectively the solid angles and effective areas covered by the output optics.
NUMERICAL CALCULATIONS FOR OH
The relative intensity of the (0, 0) band at different temperatures (the data plotted corresponds to the use of a wide, rectangular slit function). Comparisons were made of the 7090 calculations with Dieke and Crosswhite's data for the relative line intensities overall.
EXPERIMENTAL FACILITIES
General overview of the experimental equipment from the high-pressure drive section of the shock tube. The housing under the operator's compartment houses the main part of the gas handling system. A semi-aluminized thin quartz disk served as a beam splitter in the path of emission from the end window of the shock tube (see Figure 5), and quartz lenses were used to focus the end window image onto the entrance slits of the monochromator. .
Quartz condensing lenses were used to focus the light from the output slits of the monochromators onto RCA 1P28 photomultipliers. However, mixtures of argon and water vapor prepared in external mixing systems show excessive preferential adsorption of the water vapor on the walls of the gas handling equipment and the shock tube during the inflow procedure. This was done by using the vapor pressure above bubbles of liquid water to cause diffusional mixing of the water vapor and argon in the test section.
Schematic representation of the gas handling and flushing system for the argon-water vapor test gas mixtures. Evaporation of the ice in the trap to a calibrated fraction of the volume of the analysis system provided a pressure reading indicating the water vapor concentration. The ratio of relative sensitivities of the two optical systems required for the data reduction was obtained directly from .
EXPERIMENTAL RESULTS
A typical oscilloscope recording from a shock tube test observing the OH emission in the axial direction behind the reflected shock wave. This location corresponds to a time interval of approx. 70)-l after the reflected shock leaves the end plate and is thus approx. in the middle of the 200.us test time for the axial observations shown in fig. ll. The linear growth of intensity observed in the axial runs, coupled with the stable signal during the early part of the cross-tube observations at the window location 1.80 inches from the end wall, indicates that the gas is transparent, isothermal, and in thermal equilibrium during the time interval 2 OO) .I.S required for the spectroscopic temperature measurements.
12, Oscilloscope view of the OH emission behind the reflected shock, viewed perpendicular to the axis of the shock tube at 1.80 inches from the end wattl. The error due to uncertainties in the monochromator setting is approximately 25 to 30°K, as discussed in Chapter III (On Theoretical Considerations). 4 it can be seen that this uncertainty in K/K causes an uncertainty of about ±30°K in the spectroscopic temperature.
The comparison between the spectroscopic and equilibrium temperatures shown in Table 1 varies by more than ±75°K in some cases, presumably because there are uncertainties in the shock tube performance data (such as measured shock velocities and initial mixture temperatures). A ±lo/o variation in the measured shock velocity causes a variation of about ±65°K in the calculated reflected shock temperature, while a 2°C uncertainty in the initial temperature causes a variation of about 25°K behind the reflected shock. In the previous shock tube temperature measurements made, Gaydon and his colleagues concluded from their line reversal study (13) that the actual temperature behind the incident shock wave agreed with the calculated values for the temperature within about ±30°K. range from 2000 to 2800 K.
CONCLUSJONS
Similar values (15 to 30 µs) were observed in most of the experiments, which were performed over a relatively small temperature range. These observed relaxation times are in approximate agreement with the experimental data from Ref. 27 and also with values calculated from the Schwartz-Slawsky-H;erzfeld rr1ethod(34 . ) assuming reasonable collision diameters.
Wilkerson, Use of the shock tube as a spectroscopic source with an application to gf-Value measurement for. Mark, The Interaction of a Reflected Shock with Boundary Layer in a Shock Tube, NACA TM 1418. Gicquel, Mesure Optique des Ternp•fratures Elevees, from the AGARD meeting on High Temperature Aspects of Hypersonic Flow, Brussels, April, 1962.
Treanor, Spectroscopic Techniques for Temperature and Density Measurements in Oxygenated Flows, Cornell Aeronautical Laboratory Report no. Jacobs, Consideration of Some Cop1 Electronic Elements in Shock Tube Instrumentation, Guggenheim Jet Propulsion Center a Laboratori Meagjerues TR No. Tunnel, from AGARD meeting on High Temperature Aspects of Elow Hypersonic, Brussels, April, 1962.
INTRODUCTION
Thus, despite its apparent advantages, the use of the high-enthalpy shock tube presents important experimental problems. Oldenberg and Rieke, checking the apparatus used for the shock tube experiment, discovered an error in the absolute intensity calibration associated with internal light scattering in the monochromator. In addition, some questions arose regarding the determination of the initial mixture concentration in the shock tube (see Part I of this thesis and also Section III of this part for further discussion of these points).
The requirements for the shock tube and calibration optics are examined, and the electronic £-number for the band system is expressed in terms of the measured variables of the shock tube experiment and associated calibration. The optical system is focused on the exit window, as this is the source of the light emission to be studied. In terms of the spectral absorption coefficient, Pw, for each :>f line it contains the basis of the slit function and the optical depth, X (which is the product PoH' of the partial pressure of the radiation species, and L, the geometric path length of the emission), Eq.
Most of the intensity contribution to the signal is from the (0, 0) band with the (1,1) band contributing approx. This procedure allows the response of the detector to be measured in terms of a known flux, using the same output optics as for the shock tube measurement, thus providing the absolute sensitivity of the system. The voltage response of the system to the calibration light is given by an expression equivalent to Eq.
EXPERIMENTAL EQUIPMENT
The scattering was probably due to reflections from prism and mirror surfaces, especially the diagonal mirror M . 5 in fig. 6, which is directly in front of the output slot s2. Since only a small portion of the exit slit was actually used in the shock tube experiment (approximately 1.2 mm diameter image of the exit window falling on the 1.0 mm wide slit), all but a 2 mm vertical section of the exit slit was masked off with black paper, which reduced the spread to approx. 40o/o. Clearly, the scattering problem here was a result of the combination of the location of the monochromator's internal optics and the distribution of intensity in the calibration lamp.
A similar monochromator-detector system that was not of the Littrow type, for example a medium quartz Hilger with a. The filament's color temperature of approx. 0.65,u was measured in the usual way with an optical pyrometer and converted to true temperature {l5. An overall view of the calibration lamp and optical pyrometer in place near the shock tube driver section is shown in Fig. 11.
Because the placement of the optics was calculated according to paraxial formulas, the uniformity of the steradiance of the image of the calibration lamp filament on the end face of the shock tube only corresponds to that of the actual filament in the boundary of the exit window region. A view of the calibration lamp and optical pyrometer in place at the drive end of the shock tube. The linearity of the response of the photomultiplier output was checked at signal strengths corresponding to those of the shock tube experiments using the calibration lamp output in the visible region.
THERMODYNAMIC PROPERTIES OF THE GAS BEHIND THE SHOCK WAVE
Absolute intensity calibration was performed immediately after each shock tube experiment to ensure that all gain settings.
DISCUSSION OF RESULTS
A typical oscilloscope record for a shock tube test observing emission in the axial direction behind the reflected shock wave. Oscilloscope record of the OH emission behind the reflected shock wave, viewed perpendicular to the axis of the shock tube at 1. Experimental equipment has shown that errors in the £-number from this source are less than ± So/o.
However, the reliability of our data has been established since sufficient care has been taken to eliminate large errors from light scattering, impurity radiation, and uncertainties in test gas concentration. Furthermore, the technique of observing radiation axially behind the reflected shock wave, in a narrow core of hot gas, showed that the OH was transparent and that chemiluminescence was not present since the initial intensity rise shown in Fig. A possible source of systematic errors in the shock tube experiments, which would result in a high £ number, is the existence of an overshoot in the population of OH behind the reflected shock wave.
The spectroscopic temperature measurements of part I have shown that internal statistical equilibrium has been reached for the vibrational rotational energies of the OH at the calculated equilibrium temperature. The probability that chemical equilibrium will not be reached appears low due to the long period of relatively stable radiation observed perpendicular to the tube axis. During the 200.us test time of the linear intensity increase in the axial observations, the OH molecules undergo approximately 106.
