Numerical investigation of thermo-hydraulic performance of perforated rectangular and sinusoidal vortex generators in a double-pipe heat exchanger

Journal of Thermal Analysis and Calorimetry https://doi.org/10.1007/s10973-023-12838-2 Numerical investigation of thermo‑hydraulic performance of perforated rectangular and sinusoidal vortex generators in a double‑pipe heat exchanger Yanru Wang1 · Ji‑Jinn Foo1 · Manh‑Vu Tran1 · Sayshar Ram Nair1 · Cheen Sean Oon1 Received: 26 July 2023 / Accepted: 9 December 2023 © The Author(s) 2024 Abstract Vortex generators (VGs) are utilized in heating and cooling systems to enhance heat transfer efficiency for energy savings. This study investigates the thermo-hydraulic performance of using the rectangular vortex generators (RVG) and the sinusoidal vortex generator (SVG) with and without holes on the annular side of a double-pipe heat exchanger (DPHE) for turbulent regimes. The numerical analysis is conducted for different angles of attack (α) (15°, 45°, and 75°) and spacings between VGs (60, 100, and 300 mm). By comparing the heat transfer behavior for a given α, the RVG cases present a higher heat transfer when compared to the SVG cases, with an exception for the 15° case. The configuration with a low α and slight curvature augments flow velocities and vortex strength, thereby enhancing heat transfer efficiency. Moreover, the 15° SVGs-hole case demonstrates a higher Nusselt number compared to the no-hole case. Adding holes in the VG significantly reduces the pressure drop for the 45° and 75° cases, while it remains the same at the 15° case. Additionally, the 75° RVG case yields the highest Nusselt number among the studied cases, with an enhancement of 42.4% when compared to the smooth pipe at the Reynolds number of 5,711. The best performance evaluation criterion (PEC) is achieved by the 15° SVGs-hole case. When the effect of different spacings is examined, the spacing of 60 mm provides the highest PEC of 1.22. In short, the present study provides valuable insights for optimizing VG design and enhancing overall system performance in DPHEs. Keywords Double-pipe heat exchanger · Rectangular vortex generators · Sinusoidal vortex generators · Thermo-hydraulic performance · Vortices Abbreviations Abbreviations DPHE Double-pipe heat exchanger Nu Nusselt number PCM Phase change material PEC Performance evaluation criterion Re Reynolds number RVG Rectangular vortex generator SVG Sinusoidal vortex generator VG Vortex generator * Cheen Sean Oon 1 Department of Mechanical Engineering, School of Engineering, Monash University Malaysia, 47500 Bandar Sunway, Malaysia List of symbols Cp Specific heat (J kg−1 K−1) Dh Hydraulic diameter (mm) f Friction factor h Average heat transfer coefficient ( W m−2 K−1) k Thermal conductivity ( W m−1 K−1) L Pipe length (m) m Mass flow rate ( kg s−1) Nu Average Nusselt number Pr Prandtl number Q Average heat transfer rate (W) svg Spacing of vortex generators (mm) T Temperature (°C) x Flow direction (m) v Velocity ( m s−1) α Angle of attack 𝜌 Density ( kg m−3) 𝜇 Viscosity ( Pas) ΔP Pressure drop (Pa) Vol.:(0123456789) Y. Wang et al. Subscripts avg Average b Bulk c Cold fluid h Hot fluid i Inlet s Smooth pipe o Outlet w Wall Introduction Heat exchangers play a vital role in facilitating energy transfer for large-scale equipment or compact electronic devices. The main challenge in designing the heat exchanger system is achieving enhanced heat transfer efficiency while minimizing the pumping power requirements, particularly within limited space constraints. To address this, the use of vortex generators (VGs) as a passive heat transfer enhancement technique has been broadly investigated in various industrial applications. VGs exhibit the potential to improve heat transfer through several mechanisms. These mechanisms include secondary vortices or swirls, mixing the flow along the wall of the main flow, reducing the thickness of the thermal boundary layer, and increasing turbulence intensity [1]. These mechanisms highlight the promising capabilities of VGs in enhancing overall heat transfer efficiency in diverse engineering applications. Circular pipes have widespread applications in thermal power plants, chemical process plants, and solar heating. Ajarostaghi et al. [2] studied an innovative VG with eighteen blades and MWCNT-Fe3O4/water nanofluid in a circular pipe. They found that a higher heat transfer rate was achieved by using both VG and hybrid nanofluid techniques. Silva et al. [3] examined two types of VGs, namely, delta-winglet and rectangular-winglet VG, within a circular pipe for different angles of attack (α) (15°, 30°, and 45°). The findings demonstrated that both VGs at an α of 45° achieved the highest heat transfer, while the delta-winglet VG with an α of 30° exhibited the best thermo-hydraulic performance. Yang et al. [4] employed three longitudinal VGs in a vertical tube with an upward flow of supercritical C O2. They found that using 24-row longitudinal VGs resulted in a remarkable 73.4% enhancement in the thermal efficiency index. However, the heat transfer deteriorated when the vortices only covered a portion of the tube wall. Zhai et al. [5] explored the thermal performance of delta winglet VG pairs in a circular pipe with different pitch ratios, flow directions, and configurations. It was found that the best thermal enhancement factor was achieved through the combination of winglet configuration with common flow-down, downstream flow direction, and optimized winglet designs. In addition, the pitch ratio was crucial in affecting the Nusselt number and friction factor. Rectangular or mini-channel heat sinks have been developed for cooling electrical chips and electronic components. Most studies have focused on parameter optimizations [6–8] and proposed new configurations [9–11] of longitudinal VGs. Brodnianska et al. [12] investigated the thermal performance of cylindrical VGs in a wavy rectangular channel. The results showed that the Nusselt number increased with the reduced channel height and rising Reynolds number. Moreover, the combination of cylindrical VGs and wavy channels caused the Nusselt number to be 6.28 times higher than a smooth pipe. Datta et al. [13] examined the heat transfer behavior of longitudinal VG pairs with various inclinations and positions in a rectangular micro heat sink. The best thermal performance could be obtained by combing two pairs of longitudinal VGs with an α of 30° when the Reynold number exceeded 600. Additionally, a longer channel downstream of the second VG pair caused an increase in heat transfer due to better fluid mixing following the vortex breakup. Karkaba et al. [14] investigated VGs with different longitudinal pitches in a rectangular channel. They observed that the thermal enhancement factor could be increased by 90% by using five rows of VGs at a longitudinal pitch equal to three times the channel height. Demirag et al. [15] reported the heat transfer augmentation for the conic VG with different α, blade angles, and scale ratios in a rectangu (...truncated)