Effects of vortex generators on heat-transfer enhancement in a duct

Abstract

A quantitative estimation of heat transfer enhancement is discussed here based on the measurements of local coefficients of heat transfer and friction for air flow over a range of Reynolds number from Re= 9,400 to 28,200. Pairs of vortex generators consisting of two rectangular blades, increasing linearly in separation downstream, are aligned laterally to the flow with a spacing W. Characteristics of spanwise local coefficients are found to vary differently over two regions of W. For small W, the phase of their distribution is shifted by 90° from the patterns observed just downstream of the blades. For large W, no phase change is observed but changes of the pattern between paired blades are distinctive, and persist downstream. Overall heat transfer coefficients are more than double those for a smooth duct without generators. As a result, the performance ratio, η, the ratio of the overall heat transfer coefficient to that for a smooth duct with an equivalent pumping power, is greater than unity for all values of W.