Natural convection heat transfer and fluid flow characteristics in horizontal and vertical narrow enclosures with heated rectangular
finned base plate have been experimentally investigated at a wide range of Rayleigh number (Ra) for different fin spacings and fin lengths.
Quantitative comparisons of finned surface effectiveness (e) and heat transfer rate between horizontal and vertical enclosures have been
reported. In comparison with enclosure of a bare base plate, insertion of heat conducting fins always enhances heat transfer rate. Optimization
of fin-array geometry has been addressed. The results gave an optimum fin spacing at which Nusselt number (NuH) and finned
surface effectiveness (e) are maximum. It has been found that: (1) increasing fin length increases NuH and e; (2) increasing Ra increases-
NuH for any fin-array geometries and (3) for any fin-array geometry and at Ra > 10,000, increasing Ra decreases e while for fin-array
geometries of large fin spacing and at Ra < 10,000, increasing Ra increases e. Useful design guidelines have been suggested. Correlations
of NuH have been developed for horizontal and vertical enclosures. Correlations predictions have been compared with previous data and
good agreement was found