Masters Theses

Date of Award

5-2022

Degree Type

Thesis

Degree Name

Master of Science

Major

Mechanical Engineering

Major Professor

Trevor M Moeller

Committee Members

L. Montgomery Smith, Milt W. Davis

Abstract

Spectroscopic databases such as HITRAN and HITEMP are required to characterize the spectral parameters of chemical species to ensure accurate calculations of gas concentrations and temperatures from laser absorption spectroscopy. These databases are populated by performing spectroscopic experiments at controlled conditions. Databases lack spectral parameters for combustion species such as CO, CO2, and H2O at temperatures combustion temperatures in the mid-IR wavelength range due to difficulties in creating an experimental absorption cell capable of surviving combustion temperatures. A high temperature absorption cell was previously used at the University of Tennessee Space Institute (UTSI) for high temperature spectroscopic experiments with combustion gases. However, this cell had a temperature nonuniformity over its optical path due to the test section extending outside of the furnace. This changed the absorbance spectrum recorded and led to inaccuracies in spectral calculations using experimental data. A three-zone cell was designed to solve this issue by using a nonabsorbing nitrogen purge in the optical path of the cell outside of the uniform temperature section of the furnace. The cell was designed to withstand temperatures up to 1500 ◦C using alumina tubes, sapphire windows, and a high-temperature alumina epoxy. The ability to insert thermocouples into the test section during use was also included. Design work to ensure the constructability, usability, and integrity of the cell was performed, including determination of an appropriate test section path length for usable data, sapphire window thickness for laser transmissibility, and the design of a gas-tight stainless steel sealing flange assembly. This design was then used to fabricate a three-zone cell at UTSI for high-temperature spectroscopic experiments. Preliminary validation of the cell at high temperatures has been performed to ascertain cell integrity. A temperature profile of the cell was taken and found to be essentially uniform across the test section.

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