Experimental study of the local convection heat transfer from a wall-mounted cube in turbulent channel flow

This paper presents some results of the experimental investigation of the l ocal convective heat transfer on a wall-mounted cube placed in a developing turbulent channel flow for Reynolds numbers between 2750 < Re-H < 4970. Ex periments were conducted using a specially designed cubic assembly made of heated copper core and a thin epoxy layer on its surface. The distribution of the local heat transfer coefficient was obtained from the surface heat f lux evaluated from the heat input and computed temperature field in the epo xy layer, and from the surface temperature distribution acquired by infrare d thermography. In parallel, the flow field was studied using laser doppler anemometer and flow visualizations, aimed at correlating the local heat tr ansfer with the pow pattern and turbulence field. The complex vortex struct ure around the cube, in particular at the top and the side faces, caused la rge variation in the local convective heat transfer. The largest gradients in the distributions of the surface heat transfer were found at locations o f flow separation and reattachment. Areas of flow recirculation are typical ly accompanied by a minimum in the hear transfer coefficient. It is argued that the local temperature rise of the air in the recirculation zone is cau sed by the trapped vortex which acts as an insulation layer preventing the removal of heat from the surface of the cubes. In contrast, the intermitten t reattachment of the low-temperature shear flow was found to produce large heat transfer coefficients.