Part 1. Emissivity Calculations for CO₂. Part 2 Shock Tube f-Number Measurement for OH

Citation

Lapp, Marshall (1960) Part 1. Emissivity Calculations for CO₂. Part 2 Shock Tube f-Number Measurement for OH. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/BW2K-2M27. https://resolver.caltech.edu/CaltechETD:etd-07052006-080623

Abstract

Part 1: A model has been developed for the calculation of total emissivities of polyatomic molecules at elevated temperatures in terms of room temperature measurements and of a few parameters characteristic of the major known regions of emission. The model involves a statistical redistribution of the theoretically available intensities throughout these regions. Using this model, emissivities of CO₂ have been calculated at 600°K for optical depths up to 3 ft-atm which agree with the experimental data of Hottel within 8%. Calculations made at temperatures up to 1750°K for optical depths of 0.1 to 2.0 ft-atm agree with the experimental data within 30%.

It appears that the proposed model for calculating the emissivities of CO₂ constitutes a good approximation at elevated temperatures and that the required parameters have been obtained with fair accuracy from a semi-empirical fit to total emissivity data measured at 300°K. It is apparent that a closer correlation with empirical data could have been obtained if an "optimal adjustment" had been made for the three variable parameters by fitting our theoretical formulae to high-temperature emissivity measurements. However, this "optimal fit" would not constitute as stringent a test of our model as the calculations described in this analysis.

We note that the success of these calculations does not depend upon a fit to Hottel's data at 300°K since (a) we are able to calculate the total emissivity at 300°K with fair accuracy from spectroscopic data and (b) we are able to estimate the parameters required by our model directly from available spectroscopic information. The use of Hottel's data is adopted only as a convenience for this test calculation in order to provide a consistent check on our method of calculating emissivities at elevated temperatures.

Part 2: The f-number for the (0,0)-band of the ²Σ → ²Π transitions of OH has been found to be (0.9 ± 0.5) x 10^-3. A shock tube was used to produce hot gas samples at temperatures from 3300 to 3900°K with equilibrium partial pressures of OH of 0.004 to 0.02 atm. The emission intensities were measured photoelectrically as a function of time behind the reflected shock in a selected spectral interval. These results were then related to the f-number by means of an absolute intensity calibration.

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