Abstract
This paper introduces a comprehensive study on the hydrothermal and entropy generation performance of convergent tubes designed with different dimple shapes. The effects of the dimple shape on the flow characteristics (heat transfer and friction) are investigated using validated computational fluid dynamics (CFD) numerical modelling and simulation tools. Inside convergent tubes with different dimple designs, turbulent flows are subjected to a continuous heat flux of 40 kW/m2. Dimpled tube geometries of different diameter ratios (DR) were built within ANSYS-Fluent software (V2022 R2). Four different dimple shapes were investigated: (a) spherical, (b) cylindrical, (c) conical, and (d) stepped-conical. These dimple shapes were examined to investigate the optimal configuration with the best hydrothermal and entropy generation performance. A comparison is made against the baseline straight smooth tube case. The main performance indicators for comparison are Nusselt number (Nu), friction factor (f), and thermal enhancement factor (TEF), calculated for different Reynolds numbers, Re = 3000 to 40,000, and at different diameter ratios, DR = 1 to 2. In addition, thermal, viscous, and total entropy components, the Bejan number (Be), the enhanced entropy generation ratio (Ns,en), and the irreversibility distribution ratio (φs) are evaluated based on the selected geometrical configurations. The results showed that the dimple shape significantly affects the hydrothermal and entropy generation characteristics of convergent tubes. The best average value of the TEF was attained by convergent tubes with stepped-conical dimple shapes at DR = 1.75, which represents a 7.81% increase over the reference smooth tube (the maximum TEF value is 1.3243 at Re = 3000 and DR = 1.25). Furthermore, the minimum levels of Ns,en were achieved by tubes with stepped-conical dimples, with average reductions of 36.92% over the studied Re range. The study provides valuable insights into the design and optimization of convergent tubes with various dimple shapes for various applications.
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