Near-infrared simultaneous measurement of temperature and flow fields of a thermal plume arising in water

Abstract

Abstract This study presents a method for the simultaneous measurement of three-dimensional (3D) temperature and flow fields in water where a thermal plume arises from a small heat source. This method is based on the near-infrared (NIR) absorption imaging with a two-orthogonal-direction telecentric system at a wavelength of 1150 nm. The acquired images of each direction were separated into the absorbance images corresponding to the temperature field and the particle shadow images through a background subtraction method. To the absorbance images of the two directions, a non-axisymmetric inverse Abel transform was applied in order to reconstruct the 3D temperature fields. The temperature was determined using the temperature dependence of the absorption coefficient of water at the wavelength. The 3D flow fields were obtained by applying the particle shadow tracking velocimetry (PSTV) that consisted of particle identification, track interpolation, and particle 3D matching to the particle shadow images. The results demonstrated the 3D transient temperature profiles within the plume and the effect of forced flow on its growth direction. At the same time, the PSTV indicated that the trajectories were consistent with the mixed convection field, which was verified by numerical simulation.