Color can be expressed as a weighted combination of three attributes: hue, intensity, and saturation. Non-coherent light reflected by thermosensitive liquid crystals holds a variable hue, moving in a generally narrow temperature interval and also depending on its inclination with respect to the plane of the crystals and on the characteristics of the impinging light. In the experimental practice, uniform lighting over an extensive area and its entire view under the same angle are unfeasible. Thus, the acquired hue field is non-uniform even if the liquid crystal sheet is isothermal. However, by means of proper filtering and calibration of the color attribute, this optical technique, besides being non-intrusive and inexpensive, is capable of mapping the temperature with accuracy better than 5% of its measuring-range amplitude. A similar method can be applied for measuring the thickness of a thin liquid film. In this case, the color attribute to be processed is its intensity. In fact, the light transmitted through a dyed liquid decreases with an increasing thickness of the layer. Again, a perfectly uniform light source is unattainable and the recorded intensity field is non-homogeneous even if the liquid free surface is flat. Nevertheless, the film thickness can be determined by this color-processing procedure with accuracy better than 8% of the measuring-range amplitude, which is dictated by the utilized dyestuff concentration. Further thermo-fluid dynamic measurements performed over extensive areas could be handled with analogous methodologies: particularly, surface temperature by emitted infrared waves and void fraction in ducts by light absorption.
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