The effect surface roughness on pressure drop and heat transfer in circular tubes has been extensively studied in literature. The pioneering work of Nikuradse (1933) established the sand grain roughness as a major parameter in defining the friction factor during laminar and turbulent flows. Recent studies have indicated a transition to turbulent flows at Reynolds number values much below 2300 during single-phase flow in channels with small hydraulic diameters. In the present work, a detailed experimental study is undertaken to investigate the roughness effects in small diameter tubes. The roughness of the inside tube surface is changed by acid treatment. Two tubes of 1.067 mm and 0.62 mm inner diameter are treated with acid solutions to provide three different roughness values for each tube. The Reynolds number ranges for the tests are 500-2600 for 1.062mm tube and 900-3000 for 0.62mm tube. The results indicated no significant effect of surface roughness on 1.067mm tube for both pressure drop and heat transfer tests. In case of 0.62mm tube it was seen that with reduction in relative surface roughness values, both Nusselt number and pressure drop values reduced. Smoother tube produced lower values of Nusselt number and pressure drop than rougher tube.
Library of Congress Subject Headings
Heat--Transmission; Tubes--Fluid dynamics; Surface roughness; Turbulence; Laminar flow
Department, Program, or Center
Mechanical Engineering (KGCOE)
Joshi, Shailesh, "Effect of surface roughness on heat transfer and fluid flow characteristics at low Reynolds Numbers in small diameter tubes" (2001). Thesis. Rochester Institute of Technology. Accessed from
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