A new thermochromic liquid crystal temperature identification technique using color space interpolations and its application to film cooling effectiveness measurements
A new color-temperature identification technique using thermochromic liquid crystals (TLC) and image processing has been developed. The technique is based on the finding that there exists a one-to-one correspondence between a temperature value and a set of TLC tristimulus values (rgb) in a color space (rgb space). Calibration points expressed in terms of rgb values corresponding to various temperatures are plotted in rgb space and then interpolated to obtain a smooth space calibration curve. This space calibration curve does not generally intersect with itself, and therefore the entire reflection region, which is not effectively used by the conventional hue-capturing technique, becomes available. Also, because the calibration curve can be obtained by simple algebraic interpolation, a more complex approach such as a neural network is not required. Moreover, the acceptable region around the calibration curve is clearly defined, and so doubtful pixel information is easily excluded by controlling this region. A temperature measurement system based on this technique has been established using a CCD color camera, image analyzing application board, and Visual C++ programs. With this system, film cooling effectiveness over a flat plate through a round hole, a diffusion-shaped hole, and a diffusion-shaped hole with a vortex generator was studied.