Experimental Study of the Local Convection Heat Transfer From a Wall-Mounted Cube in Turbulent Channel Flow

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Abstract
This paper presents some results of the experimental investigation of the local convective heat transfer on a wall-mounted cube placed in a developing turbulent channel flow for Reynolds numbers between 2750 < ReH < 4970. Experiments 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 flux evaluated from the heat input and computed temperature field in the epoxy layer, and from the surface temperature distribution acquired by infrared thermography. In parallel, the flow field was studied using laser doppler anemometer and flow visualizations, aimed at correlating the local heat transfer with the flow pattern and turbulence field. The complex vortex structure around the cube, in particular at the top and the side faces, caused large variation in the local convective heat transfer. The largest gradients in the distributions of the surface heat transfer were found at locations of flow separation and reattachment. Areas of flow recirculation are typically accompanied by a minimum in the heat transfer coefficient. It is argued that the local temperature rise of the air in the recirculation zone is caused by the trapped vortex, which acts as an insulation layer preventing the removal of heat from the surface of the cubes. In contrast, the intermittent reattachment of the low-temperature shear flow was found to produce large heat transfer coefficients.