Abstract
Improving the cooling performance of internal channels is important to extend the lifespan of hot components exposed to heat in many types of machinery. This study was performed to examine the effects of placing a delta-winglet-pair (DWP) upstream of a single dimple in an internal cooling channel. The local heat/mass transfer coefficients (H/MTCs) were measured in the vicinity of the dimple by the naphthalene sublimation method (NSM). The cooling performances under laminar, transitional, and turbulent flow conditions were compared at different values of the DWP incidence angle (β). The DWP enhanced local H/MTCs within the dimple cavity due to intensified secondary vortices. With increasing the DWP incidence angle, the distance between the symmetrical vortices increased resulting in a different level of H/MTC enhancement. The optimum DWP incidence angle ranged between 30∘<β<45∘ depending on the flow condition. The resulting area-averaged H/MTCs clearly indicated enhancement from the DWP. Under the laminar flow conditions, the H/MTCs were enhanced by 87%–125% from installing the DWP. The absolute H/MTCs were highest under the transitional flow conditions. Based on the present investigation, the installation of the DWP in the dimpled channel is highly recommended for both laminar and transitional flow conditions.
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