Experimental investigation of the effect of flexible/rigid flag on heat transfer

Abstract

This experimental work investigated the heat transfer characteristics of rectangular channels equipped with a flexible flag vortex generator (FFVGs) and a rigid flag vortex generator (RFVGs). The FFVGs and RFVGs are mounted at the entrance of the channel using four different obstacle geometries. The experiments were per-formed in a rectangular duct with FFVGs and RFVGs under four different Reynolds numbers (9965, 19,930, 29,985, and 34,875), four different obstacle geometries (triangle-shaped obstacle (T-SO), cylinder-shaped obstacle (C-SO), rectangular-shaped obstacle (R-SO) and half cylinder-shaped obstacle (HC-SO), four different FFVGs and RFVGs lengths (L) (50 mm, 100 mm, 150 mm, and 200 mm), four different FFVGs and RFVGs width (w) (10 mm, 20 mm, 30 mm, and 45 mm), and two different FFVGs and RFVGs channel height clearance (c) (1 mm, and 4 mm). To reduce the number of trials, the Taguchi technique was utilized, thereby reducing the number of trials from 1024 to 16. The highest thermal performance factor was determined as approximately 1.32 in Case 12, which was observed in Case 12 with, l* = 0.36, w* = 0.036, c* = 0.014, Re = 34,875, FFVGs, and R-SO. The heat transfer results of the FFVGs and RPVGs were compared with those of a smooth plate. The best heat transfer performance was obtained with the FFVGs. The presence of the vortex generators produced higher heat transfer coefficients than the smooth plate surfaces.