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

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 $$0\le \phi \le 0. 0 4$$ and mean diameter of $$28 \le D_{\text{p}} \le 82\,{\text{nm}}$$ , 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 $$\phi$$ and $$D_{\text{p}}$$ . 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 $$\phi$$ and $$D_{\text{p}}$$ increase. The results of the current work are believed to be useful for the efficient design of thermal equipment using nanofluid as working medium.