Heat Transfer and Pressure Loss Measurements in a Turbulated High Aspect Ratio Channel With Large Reynolds Number Flows

Abstract

Experiments to investigate heat transfer and pressure loss are performed in a rectangular channel with an aspect ratio of 6 at very high Reynolds numbers under compressible flow conditions. Reynolds numbers up to 1.3 أ— 106 are tested. The presence of a turbulated wall and the resultant heat transfer enhancement against a smooth surface is investigated. Three dimpled configurations including spherical and cylindrical dimples are studied on one wide wall of the channel. The presence of discrete ribs on the same wide wall is also investigated. A steady state heat transfer measurement method is used to obtain the heat transfer coefficients while pressure taps located at several streamwise locations in the channel walls are used to record the static pressures on the surface. Experiments are performed for a wide range of Reynolds numbers from the incompressible (Re = 100,000–500,000; Mach = 0.04–0.19) to compressible flow regimes (Re = 900,000–1,300,000, Mach = 0.35–0.5). Results for low Reynolds numbers are compared to existing heat transfer data available in open literature for similar configurations. Heat transfer enhancement is found to decrease at high Re with the discrete rib configurations providing the best enhancement but highest pressure losses. However, the small spherical dimples show the best thermal performance. Results can be used for the combustor liner back side cooling at high Reynolds number flow conditions. Local measurements using the steady state, huedetection based liquid crystal technique are also performed in the fully developed region for case 1 with large spherical dimples. Good comparison is obtained between averaged local heat transfer coefficient measurements and from thermocouple measurements.