LOCAL AND GLOBAL HEAT TRANSFER CHARACTERISTICS INSIDE A RECTANGULAR CHANNEL OF 1:10 ASPECT-RATIO WITH RIBBED SURFACES

In this paper we present new experimental results on both local and global 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 on the lower wall, that is also the only one heated. As local heat transfer characteristics are evaluated for fixed heat flux boundary condition whereas the global ones are for uniform wall temperature, two different test sections are used; that one for local measurements is provided with a 120 mm x 120 mm Germanium window to allow optical access inside the duct to the IR-camera. The local convective heat transfer coefficient is evaluated by accurately assessing the dispersed non-convective heat flux components. A Matlab script was specifically developed to solve the radiative heat transfer problem in a 2D cavity involving partially transparent walls and multi-wavelength regions. Moreover, much attention was also paid to evaluate the heat flux conductively diffusing through the heater plane and the walls surrounding the cavity. Data here presented refer to convection over ribs of 4-mm side in transverse configuration with a pitch-to-height ratio of 20, and for Reynolds numbers, based on the duct hydraulic diameter, ranging between 700 and 8000. Finally, the stream-wise distributions of the local heat transfer coefficient are shown and compared to the flat channel.