Investigation of Pressure Drop and Heat Transfer Behavior of a Square Channel with 45° Angle Ribs at Wide Range of Reynolds Numbers

An experimental investigation of the friction and heat transfer behavior for a fully developed flow in a square channel was conducted under a wide range of Reynolds numbers (Re) from 6,000 to 180,000. The test section was 22 hydraulic diameters (Dh) long, and made of four aluminum plates. The interior comprised of two opposing rib roughened walls and two opposing smooth walls. The ribs were oriented at 45° to the flow direction, and the ratio of rib height to channel hydraulic diameter (e/Dh) and the ratio of pitch to rib height (p/e) were 0.063 and 10, respectively. A 20Dh long acrylic channel with a continuation of the test section’s interior was attached at the inlet of the test section to confirm the flow to be fully developed. For the heat transfer tests, the four walls of the test section were maintained at isothermal conditions. The friction factor, the average Nusselt number (Nu), and thermal performance of the channel were compared with the available data in the existing literature in Re ranging from 6,000 to 70,000. An extensive investigation was performed at higher Re up to 180,000. The results show that the heat transfer augmentation (Nu/Nu0) caused by the ribs approaches a constant value around 2.0 after 8.0 Dh distance in the tested Re range. However, as Re increases, the friction factor enhancement (f/f0) also increases linearly, which gradually reduces the overall thermal performance. Comparative numerical studies have also been conducted by solving Reynolds Average Navier Stokes(RANS) equations by using v-f turbulence model with all y+ wall treatment in the same range of Re as in experiment. It is found that v-f turbulence model overpredicts both the experimental heat transfer and friction results.