First average and local heat transfer measurements on a forced air-flow at low Re-numbers through a rectangular channel with ribbed surfaces

In this paper we present new experimental results on average and local heat transfer characteristics of a forced air-flow through a rectangular channel with the lower and upper surfaces with continuous, square ribs. Comparisons with data inside a flat rectangular channel are also presented. The experimental duct cross-section is 120 mm wide and 12 mm height, and the channel is operated with the lower and upper walls at fixed temperature whereas the sides are adiabatic. Ribs are transverse to the flow or tilted with an angle of 45° or 60°; for the transverse configurations, three values of the pitch-to-heigth ratio p/e, namely 10, 20 or 40, are investigated. Reynolds numbers, based on the duct hydraulic diameter, are varied between 600 and 8000. Accordingly, the average Nusselt numbers and the Darcy-Weisbach friction factor are presented. In addition, first results on local temperature measurements by means of IR-thermography, obtained in a properly modified test section operated at a constant heat flux, are shown for the transverse- rib configuration with p/e = 10 and e = 4-mm.