Performance study of spiral finned tubes on heat transfer

The study titled “Performance study of spiral finned tubes on heat transfer and wake flow structure,” published in the International Journal of Heat and Mass Transfer, investigates the turbulent flow and heat transfer characteristics of heat exchangers utilizing spiral finned tubes (SFT). The research employs large eddy simulation (LES) to analyze the flow dynamics and temperature distribution around these tubes, aiming to enhance the understanding of how vortex structures influence heat transfer efficiency.

Objectives and Methodology

The primary objective of the study is to identify coherent turbulent structures around spiral fins and to understand their role in improving heat transfer performance. The authors utilize the Q-criteria to analyze vortex structures and dynamic mode decomposition (DMD) to assess temperature variations in the flow field. The study also examines how changes in Reynolds numbers affect the turbulent flow characteristics and heat transfer coefficients.

The research is structured into several key components:

1. Numerical Simulation: The turbulent flow around the SFT is simulated using ANSYS Fluent, focusing on three-dimensional, incompressible, unsteady flow conditions.
2. Vortex Identification: The Q-criteria method is employed to identify and characterize vortex structures in the flow field.
3. Dynamic Mode Decomposition: DMD is used to analyze the modal information of temperature variations, providing insights into the flow dynamics and heat transfer mechanisms.

Key Findings

1. Vortex Structures: The study identifies three primary vortex regions around the SFT, which significantly enhance heat transfer. The flow structure is characterized by counter-rotating vortices that form due to the interaction between the fluid and the
2. Reynolds Number Effects: The research demonstrates that increasing the Reynolds number enhances the formation of small-scale eddies, which positively impacts heat transfer up to a certain point. However, beyond a specific Reynolds number, the vortex strength does not continue to increase, indicating a complex relationship between flow dynamics and heat transfer efficiency.
3. Heat Transfer Coefficients: The Nusselt number (Nu), a dimensionless measure of convective heat transfer, is found to correlate strongly with the identified vortex structures. The correlation coefficient between Nu and the Q values is reported to be as high as 0.81, indicating a robust relationship between turbulence and heat transfer performance.
4. Temperature Distribution: The temperature distribution on the fin surfaces shows significant variation, with higher temperatures observed upstream due to enhanced heat transfer in regions with strong vortex activity. The maximum Nu number reaches over 100 at specific locations on the fins, highlighting areas of optimal heat transfer.
5. Dynamic Modes: The DMD analysis reveals that the dominant modes affecting temperature distribution correspond to vortex shedding frequencies, indicating that the coherent structures play a crucial role in enhancing heat transfer.

Conclusion

The study concludes that the coherent turbulent structures around spiral finned tubes are critical for improving heat transfer efficiency in heat exchangers. The findings provide valuable insights for the design and optimization of compact finned heat exchangers, particularly in applications involving waste heat recovery. The use of advanced simulation techniques like LES and DMD offers a deeper understanding of the complex interactions between flow dynamics and thermal performance, paving the way for future research in this area.

Overall, the research contributes significantly to the field of thermal engineering by elucidating the mechanisms through which vortex structures enhance heat transfer in spiral finned tube systems.