Aerothermal characteristics of a rectangular duct with periodic trapezium ribs

Abstract

An experimental investigation of aerothermal performance, and the underlying flow mechanism in a rectangular channel mounted with trapezium ribs, has been carried out at a Reynolds number of 42500. Transient Liquid Crystal Thermography (LCT) has been employed to get the local heat transfer coefficient (HTC) distributions on the rib turbulated wall. Primarily, the effects of trapezium angle (γ = 5, 10, 15, and 20°) and pitch ratio (p/e = 6, 8, 10, and 12) have been studied on local- and spanwise averaged heat transfer fields. In addition, the performance indexes in terms of overall heat transfer enhancement factor, friction factor and overall performance factor have been compared, and found that most of the trapezium ribs (except γ = 10°) provide a better overall performance when compared to square rib (γ = 0°). However, the heat transfer characteristics are further correlated and explained by flow field quantities; i.e., ensemble averaged streamlines and mean velocities, critical flow structures, coherent structures, and fluctuation statistics, obtained by Particle Image Velocimetry (PIV) at a pitch ratio of 12. The variation in spatial distribution of thermal enhancement factor confirms the streak of reattachment, separations and recirculation bubble, which are closely related to the definable time-averaged flow structures; i.e., recirculation bubble, corner eddies, reattachment zone and the boundary layer redevelopment region. The simultaneous study of detailed aerothermal features gives confirmation with regards to the role of fluid dynamic factors in the heat transfer augmentation. © 2019 by Begell House, Inc.