Thermo-Hydraulic Performance Enhancement of Finned Elliptical Tube Heat Exchangers by Utilizing Innovative Dimple Turbulators

Abstract

As a new type of fin structure in finned tube heat exchangers, dimple turbulators exhibit excellent potential for thermo-hydraulic performance enhancement. A three-dimensional numerical simulation study was conducted to investigate the influences of five kinds of innovative concave dimple turbulators (CDTs), namely – elliptical dimple, conical frustum dimple, trapezoidal prism dimple, leeward triangular dimple and upward triangular dimple (UwTD) on the thermo-hydraulic performance enhancement in a plate fin-and-elliptical tube (PFET) heat exchanger, where CDTs are textured on the fin surface transversely between the elliptical tubes. The computational results are analyzed by considering the performance evaluation criterion for the PFET heat exchangers with different types of CDT shapes. The present investigation demonstrates that the heat transfer enhancement is intimately pertained to ejection with longitudinal counter-rotating flow, strengthened secondary flow and vortex structures at the downstream rim of CDT. A parametric study on the CDTs indicated that the UwTD vortex turbulators give better thermo-hydraulic performance under the present conditions. The numerical simulation results illustrated different secondary flow structures and heat transfer characteristics of the CDTs with various shapes, which disclosed the influential mechanisms of differently shaped dimple turbulators on the heat transfer augmentation in PFET heat exchangers.

Acknowledgments

This work was carried out at the Heat Transfer Group at the Department of Energy Sciences, Lund University by Dr. Babak Lotfi as a research affiliate under the supervision of Professor Bengt Sundén.

Additional information

Notes on contributors

Babak Lotfi is a Research Affiliate in the Heat Transfer Group at the Department of Energy Sciences, Lund University, Sweden. He received his Ph.D. in Power Engineering and Engineering Thermophysics from Xi’an Jiaotong University in 2015. His research activities include advanced compact heat exchangers, enhancement of heat transfer, fluid–structure interaction, multi–scale transport phenomena and turbulence modeling. He is an author or coauthor of several peer review scientific journal papers and international conference papers.

Bengt Sundén received his M.Sc. in Mechanical Engineering 1973, Ph.D. in Applied Thermodynamics and Fluid Mechanics 1979, became Docent in Applied Thermodynamics and Fluid Mechanics 1980, all at Chalmers University of Technology, Göteborg, Sweden. He was Professor of Heat Transfer, Lund University, Lund, Sweden 1992–2016, Head Department of Energy Sciences, Lund University, Lund, Sweden for 21 years, 1995–2016. He serves as Professor Emeritus and Senior Professor in Heat Transfer since 2016-10-01. The research activities cover compact heat exchangers, heat transfer enhancement, gas turbine heat transfer, combustion-related heat transfer including thermal radiation, CFD-methods, liquid crystal thermography, condensation and evaporation on micro-nanostructured surfaces, nanofluids, impinging jets, aerospace heat transfer, computational modeling and analysis of multiphysics and multiscale phenomena for fuel cells (SOFC, SOEC, PEMFC). He was founding and first editor-in-chief IJHEX – International Journal of Heat Exchangers (R.T. Edwards Inc., USA) 1999–2008, Associate Editor ASME J. Heat Transfer 2005–2008, Editor-in-chief Book Series – Developments in Heat Transfer (WIT Press, UK), 1995-, published more than 800 papers in journals (>350), books, proceedings, supervised 180 M.Sc. theses, 50 Licentiate of Engineering theses, 48 PhD-theses, Fellow of ASME, Honorary Professor Xi’an Jiaotong Univ., China, Guest Professor Northwestern Polytechnical Univ., Xi’an, China, Guest Professor Harbin Institute of Technology, Harbin, China, 2011 Recipient of ASME Heat Transfer Memorial Award, 2013 recipient of ASME Heat Transfer Division 75th Anniversary Medal, Donald Q. Kern Award 2016, Regional editor Journal of Enhanced Heat Transfer 2007-, Associate editor J. Heat Transfer Research 2011-, Associate editor ASME J. Thermal Science, Engineering and Applications 2010-2016, Associate editor ASME J. Electrochemical Energy Conversion and Storage 2017–2020.