Heat Transfer Laboratory

Faculty: Dr. Richard J. Goldstein

Vinod Srinivasan (webpage)

Title: Turbulent Natural Convection in a Horizontal Fluid Layer Heated From Below

Abstract

• Temperature and density gradients can be found over large length scales in oceans, the atmosphere, in the mantle below the earth's lithosphere, and in the convection layer of stars. These lead to fluid motion in the direction opposite to the body force i.e. upward. The phenomenon of natural convection is thus of vital importance in meteorology, astrophysics and geophysics. Engineers use natural convection for passive cooling of containment systems of nuclear reactors, cooling of devices such as electronic chips or as a mechanism to enhance heat transfer from heat exchanger surfaces. The case of turbulent natural convection in a horizontal fluid layer heated from below is of particular interest to scientists and applied mathematicians as a means of checking models for turbulence. The attractiveness lies in the fact that it offers a situation where the initial and boundary conditions are well-defined and there are not too many control parameters that determine the flow.
• In our laboratory, we induce turbulent natural convection by pressurizing a chamber to pressures up to 80 bar, and then taking temperature and power measurements in a fluid enclosed by isothermal surfaces on top and bottom, and insulated on the sides. One measure of dominance of buoyant forces over the viscous forces that act to damp motion in the fluid is the Rayleigh number. We attain Rayleigh numbers of the order of 1013, which is of the order of the Rayleigh number in the ocean, the earth's mantle and the atmosphere. The experimentally observed relationship of heat transfer (in terms of the Nusselt number) to the Rayleigh number can be used to validate models of turbulence, while serving as an input to more complex models of stellar and mantle convection. It is conjectured that the Nu-Ra relationship should be invariant at high enough Ra; it is this relation that we seek to determine.