Results and Discussion

The present study reports the effectiveness of color schlieren deflectometry in the characterization of buoyancy-driven convection. In this context, a direct comparison with monochrome schlieren is useful. Laser schlieren has certain disadvantages that are absent when a white light source is used. Thus, in color schlieren, one obtains the following features:
(i) Diffraction effect at a knife edge is avoided since a color filter is used;
(ii) Speckle, common in coherent optics, is not present in color-based measurements;
(iii) Three intensities (RGB) instead of one gray scale provide three-fold information and hence fundamental advantages in the measurement;
(iv) Difficulty with the CCD saturation, common when lasers are used, can be easily alleviated;
(v) The laser schlieren technique can not provide both positive and negative gradient information simultaneously contrary to that of color schlieren; and
(vi) The color filter can be designed to yield the required resolution. The attractiveness of a color image is yet another advantage. Since data analysis is based on light intensity itself, factors (i) and (ii) pose serious limitations in laser schlieren.

The validation of the measurement and quantitative analysis procedures in color schlieren is demonstrated in the following sections from an experiment on Rayleigh–Bernard convection. Additional applications related to ice cube melting in water and crystal growth from an aqueous solution are also presented.