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Particles in a linearly stratified fluid
thesisposted on 04.12.2019 by Khushal Ashok Bhatija
In order to distinguish essays and pre-prints from academic theses, we have a separate category. These are often much longer text based documents than a paper.
The settling of spherical and cylindrical particles in a linearly stratified fluid is investigated using experiments. The double-tank method is used to generate a linear stratification with a red colored dye homogeneously mixed in the heavy water tank. As a result of feeding the stratification using dyed heavy water, the concentration of dye varies with depth in the experiment tank. A powerful back-light and a digital camera are used to record the events. Assuming the concentration of dye is directly proportional to density of fluid, Beer-Lambert's law is used to generate a calibration between intensity of the light measured by the camera and density of the fluid. Using this calibration, density is evaluated in all the images captured. In the parameter space of this study, the spheres have three different wake patterns. The area of fluid disturbed by a suspension of spheres increases with Re and Fr. As a result, the amount of energy available for the mixing and the irreversible change of total potential energy in the system increases with Re, Fr and number of particles. Cylinders drag volumes of light fluid to larger depths in their wake than spheres and shed the light fluid in the form of vortices. This results in lower volumes of fluid perturbed by the cylinders. However, as the light fluid is dragged to larger depths, the amount of energy generated for mixing and the change in total potential energy of the system is higher. Spheres are thus more efficient in disturbing volumes of fluid but cylinders are more efficient in causing irreversible changes to the state of the system.