Experimental study of heat transfer and pressure loss in channels with miniature v rib-dimple hybrid structure

Abstract

In order to increase the thermal efficiency, gas turbines are designed to operate at higher temperature, which requires a highly efficient cooling structure. The dimples and ribs are effective structures to enhance the convective heat transfer in the cooling channels, which are commonly used in the gas turbine blade internal cooling and combustion chamber cooling. Despite a large number of the literature about the study of the heat transfer performance of the dimples or ribs respectively, few studies dealt with the flow and heat transfer characteristics of a hybrid structure with the ribs and dimples. In the present paper, a novel hybrid cooling structure with miniature V-shaped ribs and dimples is presented, and the flow structure, pressure loss and heat transfer characteristics of a cooling channel with the rib-dimple hybrid structure are investigated. The heat transfer characteristics are obtained using a transient liquid crystal thermography technique. The rib-dimples with three different rib heights of 0.6 mm,1.0 mm and 1.5 mm and with the dimple depth of 4mm are studied in rectangular channels within the Reynolds number range from 10,000 to 60,000. The experimental study showed that the Nusselt numbers of the channels with the rib-dimples are significantly higher than those of the channel with pure dimples. The friction factor increases rapidly with the height of V ribs. The V ribs increase the flow disturbance in the front half of the dimples, leading to an increase of the flow turbulent kinetic energy, increasing the flow mixing dramatically, and breaking out the flow recirculation zone in the front half of the dimples. Therefore the V rib-dimple hybrid structure on the cooling channel surface provides much larger heat transfer enhancement capability than the conventional dimples.