Near-infrared measurement of water temperature near a 1-mm-diameter magnetic sphere and its heat generation rate under induction heating

Abstract

This paper presents a method of measuring the temperature of water near a 1-mm-diameter magnetic sphere under induction heating. The method is based on the temperature dependence of the absorption coefficient of water at a wavelength of 1150 nm. In this study, two-dimensional images of the absorbance, which is the transverse projection of the absorption coefficient of water, were acquired by a near-infrared camera through a telecentric lens, and three-dimensional radial profiles of the temperature were then generated by applying inverse Abel transforms (IATs) to the absorbance profiles. To ensure the spherical symmetry of the temperature and the parallelity of the light rays, which are the conditions necessary to apply an IAT, the onset of free convection and the angles of deflection were evaluated. This paper also presents a method of estimating the heat generation rate in a sphere by fitting the numerical solutions of the thermal conduction equation to the measured temperatures. The temperatures and heat generation rates were observed to change consistently with the changes in the magnetic field intensity.

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

“…The NIR absorption technique is based on the principle of temperature dependence of the absorption bands of water in the NIR region. As is shown in Figure 1a, the ν 1 + ν 2 + ν 3 absorption band of water is observed in the 1100-nm to 1250-nm wavelength (λ) range and shifts to shorter wavelengths as the temperature increases 19 . Here, ν 1 + ν 2 + ν 3 means that this band corresponds to the combination of the three fundamental O-H vibration modes: symmetric stretching (ν 1 ), bending (ν 2 ), and antisymmetric stretching (ν 3 ) 20,21 .…”

“…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.…”

“…As the absorption coefficient of water at λ = 1150 nm is smaller than that at λ = 1412 nm, the former wavelength is suitable for approximately 10-mm-thick aqueous media, while the latter is suitable for approximately 1-mm-thick ones. 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 .…”

Detection of Microplastics in Water and Ice

“…The absorption bands of water and ice in the NIR had been reported as 760, 970 (or 980), 1190, 1450, and 1940 nm for liquid water and 1030 nm for water ice [35,36]. The water and ice absorbance in the NIR range increases or the peak wavelengths shift with a temperature increase, but the change is relatively small in the wavelength region between 750 and 1000 nm [37][38][39]. The absorption properties of water result from the vibration transition in H 2 O, involving various harmonics and combinations-induced asymmetric and symmetric stretch and bending mode transition by H-O-H [40].…”

Simultaneous measurement of temperature and flow field formed by a small heated sphere in water by near-infrared absorption imaging method and particle tracking velocimetry

“…This paper presents a near-infrared (NIR) imaging system that simultaneously measures the temperature and flow fields formed by a 1-mm-diameter steel sphere. The temperature is based on the temperature dependence of an NIR absorption band of water [2,3], Using this NIR-based technique with the Inverse Abel Transform (IAT) [4], we got absorbance difference images of water around the steel sphere and then estimated the temperature distribution. The flow visualization and velocity measurement are implemented by particle tracking velocimetry (PTV) [5].…”