Experimentation was conducted to examine the heat transfer and pressure drop characteristics in a rib-roughened rectangular passage with aspect ratio 2:1 for four rib configurations: 90 deg, 75 deg, 60 deg and 45 deg oblique ribs. The ribs were attached to two opposing long side walls instead of short side walls. In this study the oblique ribs were intended to function as secondary flow inducers as well as turbulators to improve the heat transfer of the bottom wall (one of the short side walls). The results revealed that, in order to enhance the heat transfer of the bottom wall, the oblique ribs should be arranged so that the secondary flow along the ribs hits the top wall instead of the bottom wall. Flow visualization test was performed to understand the heat transfer mechanisms. It was confirmed that the heat transfer enhancement at the bottom wall was attributed to the rib-induced secondary flow where the flow along the ribs hit the top wall, turned back and carried cold air from the passage core region towards the bottom wall. The highest average heat transfer was achieved for the 60 deg rib pattern due to the strong rotational momentum of the secondary flow and higher heat transfer enhancement on the rib-roughened walls in comparison to the other three rib patterns.

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The objective of this study is to investigate a heat transfer phenomenon in a straight ribroughened duct which represents a cooling passage of a modern gas turbine blade. Experiments were performed for ribs mounted perpendicularly to the main flow direction on two opposite sides of the duct for the following cases: (1) with no gaps, (2) with gaps=0.33hand (3) with gaps=1hbetween the side walls and ribs (wherehis the rib height). The heat transfer results revealed significant differences among these three cases, showing that the existence of gaps increases the heat transfer. Particularly, the local heat transfer on the wall between the consecutive ribs is higher in the near-side wall region than in the central region. To shed some light on this phenomenon, flow visualization was conducted using the particle tracer method. The flow visualization results revealed the effect of gaps on the three-dimensional flow structure between the ribs. It was concluded that this structure caused the heat transfer enhancement in the near-side wall region.