Thermal Performance Assessment of Turbulent Tube Flow Through Wire Coil Turbulators

Abstract

This paper presents characteristics of turbulent convective heat transfer in a tube fitted with wire coil turbulators. Two different wire coils are introduced: (1) with typical/uniform coil pitch ratio (CR) and (2) with periodically varying three-coil pitch ratio. Various uniform coil pitch ratios (CR = 4, 6, and 8) and two periodically varying coil pitch ratios, the D-coil (decreasing three-coil pitch ratio arrangement) and DI-coil (decreasing/increasing three-coil pitch ratio arrangement), are experimentally investigated in a uniform heat flux tube. The experiments are performed for turbulent flows with Reynolds numbers ranging between 4500 and 20,000. All of the experimental results are compared with those obtained from using the plain tube, while the thermal performance factor is evaluated under an equal pumping power constraint. The experimental results show that the use of the tube fitted with all wire coils leads to an advantage on the basis of heat transfer enhancement over the plain tube with no insert. It is also observed that the uniform-pitch wire coil with higher coil pitch ratio (CR = 8) gives a higher thermal performance factor compared to ones with lower coil pitch ratios (CR = 4 and 6). In addition, for two periodically varying coil pitch ratios, the DI-coil performs with better heat transfer rate than the uniform-pitch ratio (CR = 6) and the D-coil for all Reynolds number ranges studied. The empirical correlations developed in terms of coil pitch ratios (CR), varying coil pitch ratios (D-coil and DI-coil), and Reynolds number are fitting the experimental data within plus or minus 3% and 5% for Nusselt number (Nu) and friction factor (f), respectively. The results of the thermal performance factor for various CR, D-coil, and DI-coil values are also determined.

Acknowledgments

Smith Eiamsa-ard is an associate professor of mechanical engineering at Mahanakorn University of Technology (MUT), Thailand. He obtained his D.Eng. (mechanical engineering) from King Mongkut's Institute of Technology Ladkrabang in 2006. He has been working at MUT since 1996. He has been the head of the Mechanical Engineering Laboratory of MUT for four years. His research interests include thermal and fluid engineering, heat transfer enhancement, and computational fluid dynamics (CFD). He is currently working on the application of swirling flow on enhanced heat transfer, vortex tubes, and vortex combustors. He has co-authored more than 90 international journal and conference publications. His efforts in research and engineering education have been recognized by the Association of Private Higher Education Institutions of Thailand, with an award for the Outstanding Young researcher (2008).

Vichan Kongkaitpaiboon is an assistant professor of mechanical engineering at Mahanakorn University of Technology (MUT), Thailand. He received his B.Eng. in mechanical engineering in 1982 from King Mongkut's Institute of Technology Ladkrabang, Thailand, and his M.Sc. in industrial engineering in 1989 from California State University at Northridge. He has been working at MUT since 1994. He has been the head of basic workshop at MUT since 1996. His research interests include enhanced heat transfer in heat exchangers with turbulators.

Pongjet Promvonge obtained his Ph.D. from Imperial College, University of London, UK. He is currently an associate professor of mechanical engineering at King Mongkut's Institute of Technology Ladkrabang. His teaching and research interests include thermo-fluids, turbulence models (CFD), heat transfer, energy conservation, and combustion.