Measuring Gas Temperature in Highly Particle Laden Flow Using Terahertz Spectroscopy

We developed two methods to use terahertz (THz) spectroscopy to perform gas temperature measurement: using the area ratio of two H
₂
O vapor absorbance peaks, and using the relative time delay of the THz signal, both of which change as a function of temperature. Both methods can be used in situations with high particle loading that would block traditional laser signals and degrade thermocouple performance, as THz signals do not attenuate due to particle scattering. The absorbance peak ratios were tested in the frequency range of 0.5-0.8 THz at temperatures of 523-773 K. The relationship between the gas temperature and line strength ratio of the peaks match those calculated using the HITRAN database, but has high uncertainty due to THz source instability. The time delay was tested at a frequency of 0.5 THz and temperatures of 293-773 K, and is used to determine temperature by calculating the index of refraction of the gas. It is a more accurate method, but requires knowledge of the gas composition.