Use of tubes with helical ridges to make shell/tube heat exchangers has been an industry practice for many decades. However, understanding of thermal and flow characteristics with helical ridges is far from being sufficient. In this paper, thermal and flow characteristics of single-phase water flow in a cylindrical tube with spiral helical ridges is investigated to understand the enhancement in heat transfer and the associated penalty in the increased pressure drop. The experiments were conducted in the range of Reynolds number 3,700 to 75,000 and Prandtl number 3.8 to 10.0. The measurements show that thermal and flow characteristics are different from those reported in the literature for flow in commercial pipes with roughness. An analysis of friction factors measured in this work delineates the flow characteristics in a tube with helical ridges, which would help further explore the underlying physics. A comparison against the Moody chart and Churchill correlation indicates that the transition region covers a wider range of Reynolds number and extends into a much larger Reynolds number. It is postulated that the much wider transition region is attributed to helical ridges providing a channeling effect for the fluid flowing on the surface, which is absent for flow on a general rough surface. The heat transfer enhancements and the penalty of pressure drop measured in this work are further quantified and compared with suggested correlations available in the literature.

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