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 σ , the Rayleigh number A = g ( T 1 − T 0 ) d 3 / ( T 0 κ ν ) A = g ( {{T_1} - {T_0}} ){d^3}/ ( {{T_0}κ ν } ) , 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.