New experimental results on local heat transfer inside a rectangular channel with rib-roughened surfaces

In this paper we present new experimental results on local heat transfer characteristics of a forced air-flow through a 12-mm-height, rectangular channel of 1:10 aspect ratio, with square-cross-section ribs mounted onto the lower surface. Data are collected on a completely redesigned test section. Specifically, the electric heater is made of very thin copper tracks, in direct contact with the air flow and covering at 97.5% the channel lower surface to guarantee a very uniform heat flux. The copper tracks are laminated onto a 2-mm thick board of FR-4 glass epoxy to provide negligible heat conduction inside the plate and heat losses from its sides. Finally, the channel walls are in XPS and, into the upper one, a double glazing consisting of two 120 mm x 120 mm Germanium windows is mounted to allow optical access to the IR camera and to reduce local heat dispersions. Data here presented refer to convection over 4 mm x 2 mm ribs in transverse configuration for Reynolds numbers, based on the duct hydraulic diameter, ranging between 700 and 8000. Preliminary tests show how the new apparatus has significantly improved the quality, the ease and the quickness of the measurements.