Momentum and heat transfer characteristics of three-dimensional CuO/water nanofluid flow in a horizontal annulus: influe
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Momentum and heat transfer characteristics of three‑dimensional CuO/water nanofluid flow in a horizontal annulus: influences of nanoparticle volume fraction and its mean diameter Wei Wang1,2 · Gang Liu1 · Ben‑Wen Li3 · Zheng‑Hua Rao1 · Huan Wang1 · Sheng‑Ming Liao1 Received: 10 June 2020 / Accepted: 1 November 2020 © Akadémiai Kiadó, Budapest, Hungary 2020
Abstract Both experimental and numerical studies are unanimous in enhancing heat transfer for forced convection of nanoparticle suspensions, while the available works pertaining to buoyancy-induced heat transfer in nanofluids lead to considerably diverse or even contradictory conclusions. In this work, attempt is made to explore the influences of the presence of nanoparticles, with volume fraction of 0 ≤ 𝜙 ≤ 0.04 and mean diameter of 28 ≤ Dp ≤ 82 nm , on the three-dimensional laminar natural convection in a horizontal annulus saturated with CuO/water nanofluid. Further efforts have been made to examine the discrepancies in simulation results due to the use of different models for nanofluid properties. A FORTRAN computer code based on the finite volume method is developed for the solution of the general coupled equations. Results demonstrate that the hydrothermal behaviors of nanofluid depend strongly on the complex interaction between 𝜙 and Dp . Compared to pure water, the nanofluids especially with lower solid volume fraction and smaller nanoparticle diameter show a superior potential for improving heat transfer. In addition, the overall heat transfer is seen to be under-predicted by the classical models without considering nanoparticles’ Brownian motion, whereas the degree of underestimation progressively diminishes as 𝜙 and Dp increase. The results of the current work are believed to be useful for the efficient design of thermal equipment using nanofluid as working medium. Keywords Nanofluid · Nanoparticle mean diameter · Natural convection · Heat transfer · Horizontal annulus List of symbols cp Specific heat (J kg−1 K−1) Dp Particle diameter (m) En Enhancement of heat transfer g Acceleration due to gravity (m s−2) H Height of the annulus (m) k Thermal conductivity (W m−1 K−1) L Annular gap (m) n Time level * Sheng‑Ming Liao [email protected] 1
School of Energy Science and Engineering, Central South University, Changsha 410083, China
2
School of Energy and Power Engineering, Changsha University of Science and Technology, Changsha 410114, China
3
Key Laboratory of Ocean Energy Utilization and Energy Conservation of Ministry of Education, School of Energy and Power Engineering, Dalian University of Technology, Dalian 116024, China
Nu Local Nusselt number Nuz̄ Axially averaged Nusselt number Nu3D Overall Nusselt number p Pressure (Pa) Pr Prandtl number r Radial coordinate Ri , Ro Radii of inner and outer cylinders (m) Rf Interfacial thermal resistance (m2 K W−1) Ra Rayleigh number t Time (s) T Temperature (K) Th , Tc Temperature of heated and cooled walls (K) u Velocity component in r direction (m s−1) v Velocity component
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