Turbulent Reynolds analogy factors for nonplanar surface microgeometries

Direct measurements of turbulent Reynolds analogy factors are presented for 15 nonplanar surface microgeometries (including riblets, oscillating transverse curvature, wavy walls, and micro air bearings) for momentum thickness Reynolds numbers of 1638-2631. It is shown that certain types of nonplanar surface microgeometries will increase turbulent Reynolds analogy factors significantly above flat-plate levels. In several cases, the observed elevated heat-transfer efficiencies represent the combined effects of both heat-transfer increases and drag decreases. Generally, the results suggest that decreases of the order of 20 percent are possible in heat exchanger volume, cost, and weight for designs with extensive planar surfaces.