Effects of perforated anchors on heat transfer intensification of turbulence nanofluid flow in a pipe
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Effects of perforated anchors on heat transfer intensification of turbulence nanofluid flow in a pipe Omid Adibi1 · Saman Rashidi2 · Javad Abolfazli Esfahani3 Received: 16 March 2020 / Accepted: 13 April 2020 © Akadémiai Kiadó, Budapest, Hungary 2020
Abstract In this paper, a study is conducted to determine the influences of perforated anchors on heat transfer intensification of turbulence nanofluid flow in a pipe. Six different turbulence models are used, and the results obtained by these models are benchmarked with the existing theoretical data to select the best turbulence model. The outputs showed that the k–ε–RNG–scalable wall function model has higher accuracy and so it is selected to simulate this problem. The influences of various parameters including the addition of perforation on the anchors, the perforation diameter (in the range of 1–5 mm), the Re number (in the range of 5000–25,000), and the volumetric concentration of nanoparticles (in the range of 1–5%) on the friction factor, convective heat transfer rate, and thermal enhancement factor of Al2O3/water nanofluid flow inside the enhanced pipe with anchors are studied. The outputs indicate that the friction factor associated with the anchors decreases with creating the perforations on the anchors. The usage of nanofluid is proper from both viewpoints of the heat transfer improvement and the pressure loss penalty because all thermal enhancement factors of the system are larger than unity. At Re = 5000, the thermal enhancement factor enhances about 12.28% by boosting the volumetric concentration of nanoparticles in the range of 1–5%. Keywords Turbulence models · Anchors · Perforation · Nanofluid · Pipe · Thermal enhancement factor List of symbols A Surface (m2) C1ε Constant (= 1.44) C2ε Constant (= 1.92) D Pipe diameter (mm) d Perforation diameter (mm) Gk Generation of turbulence kinetic energy owing to average velocity gradients e Total energy (m2 s−2) f Friction factor k Turbulent kinetic energy (m2 s−2) L Pipe length (m) Nu Nusselt number (–) p Pressure (Pa) T Temperature (K) * Javad Abolfazli Esfahani [email protected] 1
School of Mechanical Engineering, Sharif University of Technology, Tehran, Iran
2
Department of Energy, Faculty of New Science and Technologies, Semnan University, Semnan, Iran
3
Department of Mechanical Engineering, Ferdowsi University of Mashhad, Mashhad 91775‑1111, Iran
u, v Velocity in x and y directions, respectively (m s−1) ui, uj Velocity components (m s−1) x, y Rectangular coordinates components (m) Abbreviations LMTD Logarithmic average of the temperature difference RNG Renormalization group SIMPLE Semi-implicit method for pressure-linked equations SST Shear stress transport TEF Thermal enhancement factor Greek symbols ε Dissipation rate (m2 s−3) λ Thermal conductivity (W m−1 K−1) μ Dynamic viscosity (kg m−1 s−1) μt Turbulent viscosity (kg m−1 s−1) σk Turbulent Prandtl number for k 𝜌 Density of fluid (kg m−3) Subscripts/superscripts bf Base fluid nf Nanofluid e Empty
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