Heat transfer enhancement for annular heat exchangers using inclined dimple configurations

This study proposes a novel configuration of inclined dimples and presents experimental and numerical investigations of its thermal-hydraulic performance and economic viability. Previous research has primarily focused on tube-side enhancements, with experimental studies restricted to the laminar flow. The work explores inclined dimple configurations in an annular flow heat exchanger under a turbulent flow regime, incorporating thermal and economic evaluation along with design optimization. The purpose is to enhance heat transfer in heat exchangers used in various applications, such as thermal power systems, refrigeration and air conditioning, and food processing. The dimple inclination angle was varied from 0° to 75°, while other geometric parameters such as pitch, height, and circumferential columns, were kept constant. Distilled water (DW) was used as the working fluid, with Reynolds numbers ranging from 8000 to 16000. The results demonstrate that the dimple inclination angle modifies flow behaviour and influences the heat transfer performance. Compared to a smooth rod, the dimpled configurations enhanced heat transfer by a factor of 1.16–2.32, while increasing the friction factor by 1.33–3.13 times. The 45° inclined dimple configuration yielded the best thermal and economic performance, with performance evaluation criteria (PEC) values ranging from 1.48 to 1.77 and an estimated cost reduction of approximately 2.01 %. These findings provide valuable insights for optimizing heat exchangers to enhance heat transfer. The proposed design opens opportunities for compact and micro-level applications and offers significant potential for use with advanced working fluids, such as nanofluids, for efficient thermal systems.