Turbulent Convection in a Fluid Heated from Below

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****Technical Abstract****Turbulent convection plays a major role in numerous geophysical, astrophysical, and industrial processes, and yet its understanding remains incomplete. The proposed work will primarily extend its investigation to fluids with Prandtl numbers Pr [(kinematic viscosity)/(thermal diffusivity)] in the range from 0.17 to 1.0 which remains relatively unexplored and which is accessible in gases and gas mixtures. This range includes the Prandtl number of 0.7 relevant to Earth's atmosphere. Investigations will be extended to samples of large aspect ratio (diameter/height) up to 20 and to exceptionally large Rayleigh numbers Ra (Ra is a dimensionless measure of the applied temperature difference) up to 10^15. The effect of rotation about a vertical axis, which introduces the Coriolis force and modifies the behavior of the system, will be studied (rotation is relevant for instance to the formation of hurricanes in Earth's atmosphere). These experiments require the construction of complex apparatus and the automatic computer control of numerous intricate processes. Thus they are an exceptionally good training ground for our young coworkers. ****Non-technical Abstract****Turbulent convection in a fluid heated from below is of utmost importance in many natural phenomena and in industry. It occurs in Earth's mantle where it contributes to the motion of continental plates and influences vulcanism. In the outer core of the Earth it determines the magnetic field in which we live. It is the important heat-transport mechanism in the outer layer of the Sun and thus impacts the temperature of our environment. It plays a significant role in many industrial processes, where its enhancement or inhibition may have significant economic consequences. These applications range from miniature heat-transport devices in computer applications to the giant cooling systems of power plants. And yet much remains unknown to the scientist and engineer about these processes. The proposed work will extend our understanding of turbulent convection to fluids with properties similar to the Earth's atmosphere; this property range has remained relatively unexplored in the laboratory. The work will also be extended to samples that are rotated about their vertical axis. The rotation will exert a force on the fluid known as the Coriolis force and thus will change the behavior of the system in a manner related to how Earth's rotation modifies the nature of hurricanes and ocean currents. These experiments require the construction of complex apparatus and the automatic computer-control of numerous intricate processes. Thus they are an exceptionally good training ground for our young coworkers, many of whom will evolve into the leaders of the next generation of scientists and engineers.