article · Journal of Thermal Analysis and Calorimetry
A numerical analysis evaluated the entropy generation of turbulent water flow inside conical tubes featuring dimpled surfaces under constant heat flux. Using computational fluid dynamics, the investigation assessed both convergent and divergent tube designs across diameter ratios from 1 to 5 and Reynolds numbers ranging from 3,000 to 40,000. Dimpled geometries produced lower total entropy generation rates than equivalent smooth tubes, with convergent arrangements yielding the highest performance gains. Specifically, convergent dimpled tubes with diameter ratios between 1.5 and 3 generated the lowest overall entropy production across all tested flow rates, averaging 0.20 watts per kelvin compared to 0.34 watts per kelvin for smooth tubes. Reductions in the enhanced entropy generation ratio reached over 50 percent at lower flow rates, demonstrating that entropy generation metrics can guide optimal tube heat exchanger designs.
Heat exchangers lose efficiency through heat transfer irreversibility and fluid friction. By designing tube surfaces and geometries that minimise entropy generation, engineers can improve thermal efficiency and reduce energy losses in fluid heating systems. Identifying specific conical tube shapes and dimpled textures that cut energy dissipation helps refine cooling and heating performance in industrial thermal systems.
This research could inform the geometry and surface texturing used by heat exchanger manufacturers and thermal system designers. Because the findings are based entirely on numerical simulations and computational models rather than physical prototyping, the technology is at an early research stage. Practical commercialisation would require physical manufacturing, experimental validation under operational conditions, and economic assessment of tube dimpling methods.
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Abstract Minimizing the entropy generation rate is one of the key performance indicators for enhancing the thermal design of heat exchangers. This paper introduces a comprehensive numerical entropy generation analysis of turbulent water flow inside—newly proposed—conical tubes with dimples subjected to a constant heat flux. The effect of different tube diameter ratios (DR = 1, 1.5, 2, 3, and 5) and flow modes (convergent and divergent tube configurations) on the thermal, viscous, and total entropy generation rates is investigated within Reynolds number (Re) range of 3 × 10 3 –40 × 10 3 using ANSYS-Fluent package. Realizable k - ε (RKE) turbulence model is adopted in this study. A well-validated 3D model was adopted to estimate the dimensionless indices: Bejan number (Be), enhanced entropy generation ratio ( N s,en ), and the irreversibility distribution ratio ( $${\phi }_{\mathrm{s}}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mi>ϕ</mml:mi> <mml:mi>s</mml:mi> </mml:msub> </mml:math> ) to characterize the entropy generation performance and to compare conical dimpled tubes to smooth ones. The results showed that total entropy production rate values for dimpled tube geometries are lower than those for the corresponding smooth ones, especially for convergent dimpled tubes. Convergent dimpled tubes with DR in the range of 1.5–3 achieved the lowest total entropy production values over the whole Re range, with an average value of 0.20 W K −1 , as compared to an average value of 0.34 W K −1 for the smooth configurations. The average N s,en values for dimpled convergent tubes with DR = 1.5–3 are 0.46 and 0.80 at Re = 3000 and 40,000, with reductions of 50.54% and 3.61% at both Re values, respectively. The study also showed that the entropy generation analysis could provide an effective tool to highlight the optimal design of tube heat exchangers based on the minimum entropy generation and the enhanced entropy generation ratio.
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DOI: 10.1007/s10973-023-12127-y
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