ISSN Online: 2377-424X
International Heat Transfer Conference 12
Thermally Driven Turbulent Boundary Layer in Air along a Vertical Plate Heated at High Temperatures
Sinopsis
The turbulent characteristics of a natural-convection boundary layer in air along a vertical plate heated at high temperatures have been experimentally investigated. The two-dimensional velocity vectors and instantaneous temperature in the boundary layer at the wall temperature Tw up to 300°C were measured by using a particle image velocimetry and a cold wire. For the ambient fluid temperature T∞ of approximately 20−30°C , the maximum value of non-dimensional temperature difference βΔTw [=β (Tw − T∞)] reaches 0.90. From the correlation between the local Nusselt number Nux and the local Grashof number Grx, it is found that the heat transfer rates even for βΔTw = 0.90 are well expressed by the empirical formula obtained for the small value of βΔTw. The profile measurements of turbulent quantities for βΔTw = 0.89 have a resemblance to those observed at low wall temperatures, thus the effects of a strong heating on the turbulent behaviour in the boundary layer are quite small. Through the higher-order statistics, such as skewness and flatness factors of fluctuating temperature and velocity vectors, it is also revealed that the structure of the large-scale fluid motions in the outer region of the natural-convection boundary layer, which is closely connected with the turbulence generation, is maintained even under the condition of high wall temperatures.