Review: Applications of infrared thermography for studying flows with participating media

Abstract Infrared thermography can be used to provide useful insights into the characteristics of flows containing participating media (e.g., CO2, H2O vapor, CO, CH4, etc.). What can make this technique advantageous when compared to many other non-intrusive methods is that the measurements are quantitative, can often be readily implemented (e.g., hours), and can be applied to environments where other measurement approaches may not be practical or feasible (e.g., study wildfires, exhaust plumes, etc.). The objective of this article is threefold: 1) illustrate how infrared thermography can be applied to study the behavior of flows with participating media in fundamental or more practical applications, 2) articulate limitations and advantages of the technique, and 3) consider potential applications. Infrared thermography can be used to study flows with size characteristics ranging from millimeter to meters, and concentrations and temperatures ranging from room to peak combustion values. Both quantitative and qualitative insights into flow characteristics can be obtained from the measurements of radiation intensities. Scalar values (e.g., temperature, species concentrations) and their distribution within flows can be determined through application of inverse and deconvolution techniques. Values derived using infrared thermography tend to have lower spatial and scalar resolution than values determined using laser diagnostics, however, infrared thermography often can be applied more readily. The reduced resolution for infrared thermography results from the line-of-sight nature of the measurements and the indirect nature of determining scalar values. The quantitative nature of infrared thermography allows it to be applied to directly evaluate CFD simulations. Using infrared thermography to evaluate simulations can be particularly valuable when the scale or location of the experiments limit the application of other techniques (e.g., large exhaust plumes). Care should be exercised in evaluating CFD simulations using radiation intensity measurements because multiple solutions of scalar values can provide agreement with measured values. Infrared thermography can be applied to study high temperature and highly transient environments within or from more practical devices (e.g., combustor). The application of infrared thermography to study flows with participating media is expected to expand because of the unique capabilities compared to other passive imaging techniques.