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10 November 2003 Diffractive optical element based sensor to measure small diffusion coefficients
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In studying hydrodynamic instabilities between two miscible fluid mixtures one often faces the problem of assigning a reliable value to very small diffusion coefficients. As for diffusion between two binary mixtures such as water and glycerin, water and salt, etc., no complete data are available in the literature. In order to measure small diffusion coefficients of miscible fluids, in this paper we propose an improved version of digital projection moire. The system uses a fringe generator realized with a diffractive optical element (DOE). The fringe patterns are projected on the bottom of a ground glass plate. The phase object (diffusion cell) is placed in front of the ground glass (in other words, in front of the fringe pattern), which is imaged by a digital video camera. Grating patterns, during the evolution of diffusion phenomena, are captured by a CCD camera and stored in a computer at different times. With the aid of Fast Fourier Transform (FFT) and signal demodulating techniques, the images are processed to obtain the diffusion coefficients. The theoretical basis of the device is presented. Furthermore, we report some experiments conducted for demonstrating the usefulness of the system.
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Giuseppe Schirripa Spagnolo, Dario Ambrosini, and Domenica Paoletti "Diffractive optical element based sensor to measure small diffusion coefficients", Proc. SPIE 5191, Optical Diagnostics for Fluids, Solids, and Combustion II, (10 November 2003);

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