Natural convection in rectangular cavities is studied for the aspect ratio range of 1–6.

Cavity length largely affects the heat transfer.

Average Nusselt number changes with the aspect ratio.

Local Nusselt number is affected by the position of the local heat sink.

Heat transfer correlations are presented for the Rayleigh number range of 2.16 × 10⁵ to 5.06 × 10⁷.