Dependence of boundary layer thickness on layer height in laminar and transient convective regimes

Dependence of boundary layer thickness on layer height in laminar and transient regimes is studied for convection from localised heat source with an open surface. The measurements of Nusselt number and characteristic frequency of thermal plume formation are done for a wide range of Rayleigh number, different Prandtl numbers and different aspect ratios. The obtained results prove that for the developed (but not turbulent) convective flow the boundary layer thickness is almost independent of the layer height and it is mainly defined by applied temperature difference and physical properties of the fluid.