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A laboratory study of thermal convection under a central force field Chandra, Bhuvanesh

Abstract

This thesis presents the results of a theoretical and experimental study of thermal convection under the influence of a central force field. Flows in the atmosphere and in the core of the earth are thought to occur under a near balance between Coriolis and buoyancy forces. Thus, a desirable model of these flows would include spherical symmetry in the force field and rotation. The present study, in which convection under a central force field in cylindrical geometry has been achieved, is the first step towards such a model. The system consists of a cool outer cylinder and a hot inner cylinder with a dielectric liquid (silicone oil) filling the annulus between them. The common axis of the cylinders is vertical. The inner cylinder is grounded and the outer cylinder is kept at a high alternating (60 Hz) potential. This intense alternating electric field provides the radial buoyancy force which results in convective heat transfer at a certain critical temperature gradient. The fluid in the system is found to behave like a layer of fluid in a gravitational field, heated from below. Below a certain critical value of a dimensionless number (equivalent to the Rayleigh number with the electrical force substituted for gravity) there is no convective heat transfer. Above the critical value, flow sets in with the convective heat transfer proportional to the modified Rayleigh number. Marginal stability analysis gives a critical electrical Rayleigh number in agreement with the experimentally determined value.

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