Three-dimensional temperature measurement in turbulent thermal convection by extended range scanning liquid crystal thermometry

The usable temperature range of liquid crystal thermometry has been extended and used to measure three-dimensional temperature fields in turbulent thermal convection. The color of the liquid crystals is calibrated against temperature using the standard method in which hue is the single input variable and two new methods: hue/intensity as input variable, and hue, saturation and intensity as input variables to a neural network. Relative to the hue calibration, the new methods extend the range over which temperature can be measured by more than 100%. Three-dimensional temperature measurements of turbulent thermal convection over smooth surfaces were carried out at a flux Rayleigh number of 3 × 109 by scanning a white light sheet normal to the visualized image plane and capturing a number of sequential images at various positions of the light sheet. Stacks of the planar data were composed into three-dimensional temperature distributions. The results indicate the presence of an irregular spoke pattern over the surface and the generation of plumes from the intersections of the patterns, consistent with other investigations.