TED-AJ03-370 Planar Measurement of Local Characteristics of Impinging Spray on Heating Plate :

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For the investigation of the dispersed two-phase flow with small droplets or bubbles, particle size, velocity and their spatial distribution are the significant properties and therefore they are the most frequently measured quantity to understand the flow structure and to evaluate the transport process. Especially, the particle motion near the isothermal or hot wall is of interest in the applications of fuel injection in IC engine, mist cooling for a material processing. The paper describes the application of planar droplet sizing technique of the spray impinging on a hot plate. Interferometric laser imaging for droplet sizing (ILIDS) is the method that provides an instantaneous spatial distribution of droplet size by analyzing the out-of-focus image of droplets. The number of fringes or inter-fringe spacing in the image is linearly correlated to individual diameters. The measurement accuracy depends on the estimation of the size of circular image and the fringe spacing. The relation between fringe spacing and droplet size was derived by noting the angular phase difference of the external reflection from the surface and the direct refraction through the droplet. Conventional ILIDS techniques, which observed the circular image with fringe on a film, have difficulties in discriminating the fringe images due to the confusion by overlapping among them. In the present technique, and advanced imaging technique and accelerated data processing by fast computer system was proposed that the circular images with fringes are optically squeezed into the linear images by defocusing horizontally and focusing vertically. The present squeezing technique reduced the involved noise and the signal to noise ratio of the interferogram becomes much better than that of conventional technique as the consequence. Moreover, the compression equipment can eliminate the distorted or inclined interference signal by the wall reflection and the multiple scattering. T he preferential acquisition function of the squeezing technique provides the genuine interferential signal that gives a diameter of particle. The linear interferogram is detected by scanning the horizontal pixels of the recorded image. The signal processing procedure for the determination of the particle diameter requires only one dimensional information of the fringe spacing by discrete Fourier transform and interpolation technique for the power spectrum so that the second order accuracy of a droplet size could be accomplished. The technique was applied to the measurement of the spray impinging on a heating plate and the experimental results showed the significant difference of the local characteristics of droplet diameter and velocity distribution.

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