Heat transfer by free convection across a closed cavity between vertical boundaries at different temperatures

The two-dimensional convective motion generated by buoyancy forces on the fluid in a long rectangle, of which the two long sides are vertical boundaries held at different temperatures, is considered with a view to the determination of the rate of transfer of heat between the two vertical boundaries. The governing equations are set up; they reveal that the flow is determined uniquely by the Prandtl number σ, the Rayleigh number A = g (T 1 − T 0) d 3 / (T 0 κ ν) A = g ({T₁ - T₀}) d³/ ({T₀ }), and the ratio of the sides of the rectangle l / d l/d. In the case of cavities used for thermal insulation of buildings, which is kept specially in mind throughout the paper, A A is usually about 1000 d 3 ^3 (where d d is in centimeters), and l / d l/d takes values between about 5 and 200.