Thermal boundary-layer structure in laminar horizontal convection

We present experimentally obtained time-averaged vertical temperature profiles in horizontal convection (HC) in water (Prandtl number), which were measured near the heating and cooling plates that are embedded in the bottom of HC samples. Three HC rectangular samples of different sizes but the same aspect ratio (, and are the length, width and height of the sample, respectively) were used in the experiments, which allowed us to study HC in a Rayleigh-number range. The measurements revealed that above the cooling plate, the mean temperature profiles have a universal scaling form with being a-dependent thickness of the cold thermal boundary layer (BL). The-profiles agree well with solutions to a laminar BL equation in HC, which is derived under assumption that the large-scale horizontal velocity achieves its maximum near the plate and vanishes in the bulk. Above the heating plate, the mean temperature field has a double-layer structure: in the lower layer, the profiles scale with the hot thermal BL thickness, while in the upper layer, they again scale with. Both scaling forms are in good agreement with the solutions to the BL equation with a proper parameter choice.