Heat Transfer Enhancement in Flue-Gas Systems with Radiation-Intensifying Inserts: An Analytical Approach

Justina Menkeliūnienė (), Rolandas Jonynas, Linas Paukštaitis, Algimantas Balčius and Kęstutis Buinevičius
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Justina Menkeliūnienė: Department of Energy, Faculty of Mechanical Engineering and Design, Kaunas University of Technology, 51424 Kaunas, Lithuania
Rolandas Jonynas: Department of Energy, Faculty of Mechanical Engineering and Design, Kaunas University of Technology, 51424 Kaunas, Lithuania
Linas Paukštaitis: Department of Energy, Faculty of Mechanical Engineering and Design, Kaunas University of Technology, 51424 Kaunas, Lithuania
Algimantas Balčius: Department of Energy, Faculty of Mechanical Engineering and Design, Kaunas University of Technology, 51424 Kaunas, Lithuania
Kęstutis Buinevičius: Department of Energy, Faculty of Mechanical Engineering and Design, Kaunas University of Technology, 51424 Kaunas, Lithuania

Energies, 2025, vol. 18, issue 13, 1-23

Abstract: A significant portion of energy losses in industrial systems arises from the inefficient use of high-temperature exhaust gases, emphasizing the need for enhanced heat recovery strategies. This study aims to improve energy efficiency by examining the effects of radiation-intensifying inserts on combined radiative and convective heat transfer in flue-gas heated channels. A systematic literature review revealed a research gap in understanding the interaction between these mechanisms in flue-gas heat exchangers. To address this, analytical calculations were conducted for two geometries: a radiation-intensifying plate between parallel plates and the same insert in a circular pipe. The analysis covered a range of gas-flue and wall temperatures (560–1460 K and 303–393 K, respectively), flow velocities, and spectral emissivity values. Key performance metrics included Reynolds and Nusselt numbers to assess flow resistance and heat transfer. Results indicated that flue-gas temperature has the most significant effect on total rate of heat transfer, and the insert significantly enhanced radiative heat transfer by over 60%, increasing flow resistance. A local Nusselt number minimum at a length-to-diameter ratio of approximately 26 suggested transitional flow behavior. These results provide valuable insights for the design of high-temperature heat exchangers, with future work planned to validate the findings experimentally.

Keywords: turbulator; insert; energy efficiency; flue-gas flow; radiative heat transfer; convection; passive heat transfer enhancement (search for similar items in EconPapers)
JEL-codes: Q Q0 Q4 Q40 Q41 Q42 Q43 Q47 Q48 Q49 (search for similar items in EconPapers)
Date: 2025
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