Aqueous suspensions of Milling Yellow dye have been found to lie useful for engineering flaw studies by employing established birefringent techniques. In the present work, the basic birefringent and rheologic properties of Milling Yellow suspensions wore measured for a range of deformation rates important to the engineering applications. A concentric‐cylinder polariscope was used to measure the amount of birefringence and the angle of extinction for ten Milling Yellow suspensions at 25°C. varying in concentration from 1.25 to 1.46% dye by weight. The optical properties exhibited by these suspensions are similar to those of a number of colloidal suspensions as reported by past investigators. Rheologic data for Milling Yellow suspensions in the same concentration range were measured at 25°C. for deformation rates of 50–10 sec.−1 by means of a capillary viscometer. Over the complete range of deformation rates the rheologic data are accurately described with the Powell‐Eyring relationship for pseudo‐plastic materials.
An experimental technique for the determination of velocity distributions in two-dmensional laminar flow is described. The method utilizes the optical interference patterns observed in flowing doubly refracting liquids when viewed by transmitted polarized light. The fluid shear-stress distribution may be determined from these interference patterns by methods similar to those employed in solid photoelasticity. Methods are presented for the calculation of velocity distributions from the observed stress distributions. Experiments are described in which the technique was applied to determine velocity profiles in parallel-walled, converging and diverging channels and for flow about a cylindrical obstacle. The doubly-refracting liquids employed were aqueous solutions of an organic dye. Independent experimental checks were obtained in most instances, and these are i n satisfactory agreement with the calculated results.
The local mass transfer rates from a sphere in a regular packing array have been determined by measuring the local radius change of a slightly soluble 1.500-in. diameter benzoic acid test sphere after having been immersed in a water stream. Results in the form of typical local Sherwood number profiles are reported for single spheres over a particle Reynolds number range of 166 to 1,560, and for spheres in simple cubic packing and rhombohedral packing over particle Reynolds number ranges of 488 to 2,409 and 1,680 to 3,410, respectively. All runs were made a t room temperature. An idealized flow pattern around spheres in simple cubic packing is presented.Although extensive work has been done on various overall transport phenomena, such as the overall mass and heat transport from randomly packed beds to flowing fluids (1, 6, 9, 10, 12, 16,18,20) and from single particles such as single spheres (8, 10) or cylinders to flowing fluids, only limited references to previous investigations of the local transport phenomena from spheres in packed beds to flowing fluids are known. It was the objective of this work to investigate the local rates of mass transfer from slightly soluble spheres in a packed bed to a flowing fluid. By application of an appropriate analogy between heat and mass transfer and the local heat and mass transfer, the local heat transfer characteristics in a packed bed of spheres can be predicted from corresponding local mass transfer characteristics that can be more readily investigated in the laboratory. The present work was limited to investigation of two ordered arrays of spheres, the simple cubic packing having a void fraction of 0.47 and the rhombohedral packing having a void fraction of 0.26. These two arrays are the limiting packings expected in a bed of randomly packed spheres that has an average void fraction of 0.38 to 0.40. THEORYIn the investigation of the local rates of mass transfer from slightly soluble spheres in a packed bed molecular diffusion, natural convection mass transfer and forced convection mass transfer may be of importance at a given location on a sphere. Of course, with a fluid flowing through the packed bed, it would be expected that the primary mechanism of mass transfer would be by forced convection. However, in regions on a sphere adjacent to a point of contact between spheres, the theory of real fluids indicates that fluid velocities are very low. Hence, one would expect that mass transfer would be due primarily to the mechanisms of molecular diffusion and natural convection in these regions. Since the mass transfer coefficients for molecular diffusion are orders of magnitude less than those for forced convection, one would expect a large variation in the local mass transfer rates from a slightly soluble sphere in a packed bed. It is this variation of local mass transfer rates that is the subject of this investigation.For the present case of a slightly soluble sphere, the time-average rate of mass transfer from the sphere surface to the flowing stream could be determined ...
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