Heat Transfer Laboratory
Faculty: Dr. Richard J.
Title: Turbulent Natural Convection in a Horizontal Fluid Layer Heated From Below
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
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.