Reconstruction of cross-sectional temperature distributions of water around a thin heating wire by inverse Abel transform of near-infrared absorption images

Near-Infrared Temperature Measurement Technique for Water Surrounding an Induction-heated Small Magnetic Sphere

“…This change in the spectrum indicates that the most temperature-sensitive wavelength in the band is λ ≈ 1150 nm. Other absorption bands of water also exhibit similar behavior with respect to the temperature 15,16,17,18,20,21 . The ν 1 + ν 3 band of water observed within the range λ = 1350−1500 nm and its temperature dependence are shown in Figure 1b.…”

“…Convert Δµ i (r) to temperature via the following equation: (5) with the temperature coefficients of water, α f , which are 4.0 × 10 -3 K -1 mm -1 for λ = 1150 nm 19 and 4.1 × 10 -3 K -1 mm -1 for λ = 1412 nm 17 . Note: The command script file for running Steps 2.2.5 through 2.2.7 is presented in Supplement 4, where the Levenberg-Marquardt nonlinear least-squares algorithm 17,19 is employed for Step 2.2.5.…”

“…Alternatively, the surface temperatures of media have been remotely measured via infrared radiation thermometers to estimate the inner temperatures 14 . However, when a medium containing a small heat source is a water layer or a non-turbid aqueous medium, we have demonstrated that a near-infrared (NIR) absorption technique is useful to measure the temperatures 15,16,17,18,19 . This paper presents the detailed protocol of this technique and representative results.…”

“…Recently, using λ = 1150 nm, we obtained the temperature distributions in a 10-mm-thick water layer containing an induction-heated 1-mm-diameter steel sphere 19 . Moreover, the temperature distributions in a 0.5-mm-thick water layer have been measured by using λ = 1412 nm 15,17 .…”

“…An advantage to the NIR-based temperature imaging technique is that it is simple to setup and implement because it is a transmissionabsorption measurement technique and needs no fluorophore, phosphor, or other thermal probe. In addition, its temperature resolution is less than 0.2 K 15,17,19 . Such a good temperature resolution cannot be achieved by other transmission techniques based on interferometry, which have often been used in heat and mass transfer studies 22,23,24 .…”