Heat transfer enhancement mechanism in a rectangular passage with V- and Λ-shaped ribs

Heat transfer measurement and flow visualization tests were perfomed to investigate heat transfer enhancement mechanisms of angled ribs mounted on two opposite walls of a rectangular passage with turbulent flow. Seven rib configurations were studied:90°, 60°, 60° V-shaped, 60° A-shaped and the broken arrangements for these 60° rib configurations. It was found that the rotational direction of the secondary flow induced by the ribs plays a dominant role in determining the heat transfer performance. If the rotational direction of the secondary flow is to convey fluid from the central core region of a passage directly to the heat transfer wall, the heat-transfer performance of the wall is augmented appreciably. This is attributed to (1) transportation of colder fluid from the core region to the heat transfer wall and (2) suppression of separated regions behind the ribs through the introduction of higher momentum fluid from the core region of the channel. The mechanism clearly showed the heat transfer superiority of V-shaped ribs over A-shaped ribs. The effects of the rib-induced secondary flow are very strong and remain even if the rotation conditions are employed.