Investigation of the roughened target plate to enhance the impingement heat transfer with reduced pressure loss

Impingement/effusion cooling systems are widely used in gas turbines owing to their extremely high cooling effectiveness. However, excessive flow resistance has become an obstacle to its wider application. Previous studies have focused more on improving the heat transfer performance, usually without focusing on its pressure loss. In this paper, a novel roughened target plate is proposed to improve heat transfer while reducing pressure loss. Two novel streamlined roughness elements are proposed: similar round protuberances and similar trapezoid ribs. The experiments were performed using the transient liquid crystal (TLC) method, adopting the transverse heat conduction correction technique. The influence of the Reynolds number (Re) and rib height on the heat transfer performance and related pressure loss was experimentally investigated. All data were compared with the flat plate. A numerical simulation was also conducted to provide flow field analysis to explain the enhancement mechanism. The results show that the protuberance can shorten the jet-to-plate distance to enhance heat transfer in the stagnant region. The surface of the arc side of the protuberance and rib can prevent the impinging jets from making sharp turns, resulting in reduced pressure loss. The maximum enhancement for the area-averaged Nusselt number (Nu) was achieved by the highest rib. The pressure loss for all roughened plates was lower than that of the flat plate. The rib with a moderate height provided the highest pressure loss reduction. The highest rib provided the highest heat transfer improvement at equal pumping powers of up to 26.2%. This study confirms the capacity of streamlined roughness elements to enhance impingement heat transfer with reduced pressure loss.