Papers presented to the 11th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, South Africa, 20-23 July 2015.
A numerical study of natural convective heat transfer from a horizontal isothermal square heated element with a square inner
unheated adiabatic section imbedded in a large flat adiabatic surface has been undertaken. The element is at a higher
temperature than the surrounding fluid and the cases where it is facing upward and where it is facing downward have been
considered. Steady flow has been assumed and fluid properties
have been assumed constant except for the density change with temperature which gives rise to the buoyancy forces, this
having been treated using the Boussinesq approach. The
solution has been obtained by numerically solving the
governing equations subject to the boundary conditions using
the commercial CFD solver ANSYS FLUENT©. The k-epsilon
turbulence model was used with full account being taken of
buoyancy force effects. The heat transfer rate from the heated
element expressed in terms of a Nusselt number is dependent on the Rayleigh number, the size of the inner adiabatic element
section relative to the overall size of the element, and the
Prandtl number. Results have been obtained only for a Prandtl number of 0.74, i.e., effectively the value for air. Conditions under which laminar, transitional, and turbulent flow exist have been considered. The variation of the Nusselt number with Rayleigh number has been explored in detail for various inner-
to-overall element size ratios. The results have been used to determine whether correlation equations that apply for all
inner- to-overall element size ratios can be derived.
