Acoustic Speed Measurement Platform for Monitoring Highly Concentrated Gas Temperature Distribution

Abstract

Acoustic thermography reconstructs 2-D gas temperature distributions by using sound speeds from multiple paths across a plane. However, a reliable platform that can provide accurate sound speeds in a highly concentrated temperature distribution environment has not been fully discussed. Most of the existing temperature reconstruction algorithms are developed using simulated data and validated with customized systems. The results from the reported systems are difficult to reproduce due to the lack of critical information, such as the methods for determining the time of flight (TOF). Moreover, previous attempts have not investigated the effect of a sharp temperature gradient, in which the difference of acoustic impedance between high- and low-temperature regions cannot be neglected. In response, this letter demonstrates a reliable acoustic platform designed specifically for measuring the acoustic speeds in an environment with a critical temperature distribution. The main components of the proposed platform are discussed in detail, including the TOF calculation technique, the hardware architecture, and the working principle. The performance of the platform has been evaluated by comparing the captured acoustic velocities and the reconstructed temperature map with results from a thermocouple array. The average acoustic velocity measured by the proposed platform for 100 times is <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$341 \pm \ 3$</tex-math></inline-formula> m/s at room temperature (25 °C) and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$354 \pm \ 5\ $</tex-math></inline-formula> m/s after heater turned <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">on</small> (38.27 °C). Moreover, the 2-D temperature map reconstructed by acquired acoustic velocities also matches the results from the thermocouple array. Therefore, the proposed platform can be considered as an accurate and reliable acoustic speed measurement system for monitoring the 2-D temperature distribution.