Abstract: Flow in a rectangular enclosure with three separate
heated sections on the lower surface has been numerically studied. The enclosure
considered has rectangular horizontal lower and upper surfaces and vertical side
surfaces. There are three square symmetrically placed isothermal heated sections
on the lower surface, the rest of this surface being adiabatic. The vertical
side-walls of the enclosure are kept at a uniform low temperature and the
horizontal rectangular upper surface is adiabatic. The enclosure has a width
that is twice the height of the enclosure and a depth that is equal to the
height of the enclosure. In the situation considered, a steady flow exists at
low Rayleigh numbers, an unsteady flow develops at higher Rayleigh numbers and
then the flow can again become steady at still higher Rayleigh numbers. The aim
of the present study was to try to determine the conditions under which the
unsteady flow develops and ceases and to determine the effect of the flow
unsteadiness on the mean heat transfer rate from the heated surfaces. The
solution has the following parameters: (i) the Rayleigh number, Ra,
(ii) the Prandtl number, Pr, (iii) the
dimensionless size, of the square heated sections and
(iv) the dimensionless distance between the heated sections, Results have only been obtained for
a Prandtl number of 0.7. The main interest in the present study was the effect
of on the results. The results
obtained indicate that the dimensionless heated section spacing, has a relatively strong influence
on the heat transfer rate and the conditions under which the flow first becomes
unsteady.
Keywords and phrases: natural convection, unsteady flow, enclosure, numerical, three-dimensional.
