Paper presented to the 10th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Florida, 14-16 July 2014.
Natural convective heat transfer from a square horizontal
flat isothermal heated element imbedded in a larger flat square
adiabatic surface with a square flat horizontal adiabatic surface
mounted parallel to the heated surface at a relatively short
distance from it has been numerically studied. The surface of
the heated element is in the same plane as the surface of the
surrounding adiabatic material. The square heated element
considered in this study is at a higher temperature than that of
the surrounding fluid. Both the case where the square heated
element is facing upwards and the surrounding adiabatic
covering surface is above the heated element (upward facing
case) and the case where the square heated element is facing
downwards and the surrounding adiabatic covering surface is
below the heated element (downward facing case) have been
considered. The situation considered is a simplified model of
some situations that arise in engineering practice examples
occurring in some electrical and electronic component cooling
problems. In this study, the range of conditions considered is
such that laminar, transitional, and turbulent flows occur. The
purpose of this study was to numerically determine how the
heat transfer rate from the square heated element varies with
the distance of the adiabatic covering surface from the heated
element. The solution was obtained by numerically solving the
governing equations subject to the boundary conditions using
the commercial CFD solver ANSYS FLUENT© using the kepsilon
turbulence model with full account being taken of
buoyancy force effects. Because of the applications that
motivated this study, results have been obtained for a Prandtl
number of 0.74, i.e., effectively the value for air. The effect of
the dimensionless distance between the heated element and the
cover on the variation of the Nusselt number with Rayleigh
number has been studied in detail for both the upward and the
downward facing cases.
