[1] We present new observational data on small-angle light scattering properties of natural, random shaped particles, as contrasted with spherical particles. The interest in this ''shape effect'' on scattering arises from the need for a suitable kernel matrix for use in the laser diffraction method (LD) of particle sizing. LD is now used broadly for measuring size distribution of suspended marine particles. LD involves the measurement of small-angle forward scattering at multiple angles. This data is inverted using the kernel matrix to produce size distribution. In the absence of a suitable matrix for random shaped particles, past practice has been to use a model based on Mie theory, applicable strictly only to homogeneous spheres. The present work replaces Mie theory with empirical data. The work was motivated in part by anomalous field observations of size distribution and settling velocity distributions reported in literature. We show that a kernel matrix for random shaped particles results in improved interpretation of field multiangle scattering observations. In particular, a rising edge at the fine particle end of the size spectrum is shown to be associated with shape effects.
An experimental investigation was carried out of the development of steady, laminar, incompressible flow of a Newtonian fluid in the entry region of a curved pipe for the entry condition of uniform motion. Two semicircular pipes of radius ratios 1/20 and 1/7 were investigated, covering a Dean number range from 138 to 679. The axial velocity and the component of secondary velocity parallel to the plane of curvature of the pipe were measured using laser anemometry. It was observed that, in the upstream region where the boundary layers are thin compared with the pipe radius, the axial velocity within the irrotational core first develops to form a vortex-like flow. In the downstream region, characterized by viscous layers of thickness comparable with the pipe radius, there appears to be three-dimensional separation at the inner wall. There is also an indication of an additional vortex structure embedded within the Dean-type secondary motion. The experimental axial velocity profiles are compared with those constructed from the theoretical analyses of Singh and Yao & Berger. The quantitative agreement between theory and experiment is found to be poor; however, some of the features observed in the experiment are in qualitative agreement with the theoretical solution of Yao & Berger.
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