Abstract
Recent attempts in nanoscience and technology have established nanofluid as suitable coolant for wide ranging heat transfer applications. A mathematical model is developed to study the heat transfer in rotating flow of nanofluids over an exponentially stretching plate. The purpose of undertaking this study is twofold. Firstly, to analyze the simultaneous influence of nanofluid rotation and exponential stretching on the shear stresses and heat transfer rate at the sheet which have obvious role in metal working and polymer extrusion processes. Secondly, to explore the cooling capability of water based nanofluids comprising Cu, Ag, CuO, Al2O3 and TiO2 nanoparticles for the present problem. The effective thermal conductivity of nanofluid is estimated through the Maxwell model which is valid for spherical nanoparticles. The three-dimensional Navier-Stokes equations are first simplified through classical boundary layer approximations and then non-dimensionalized through the similarity transformations. Numerical computations are made through the Runge-Kutta integration based standard shooting procedure. Newton's method is implemented to evaluate the unknown initial conditions. A comparative study of present computations with the existing literature shows an excellent agreement. It is found that both rotation and stretching have significant influence on velocity and temperature profiles. Wall shear stresses increase and heat flux from the wall diminishes when fluid is subjected to larger rotation rate. Nanoparticle volume fraction plays a significant role in enhancing cooling rate of the stretching sheet. Maximum value of heat transfer coefficient is observed for Al2O3 nanoparticles. For lambda = 1, about 27% rise in heat transfer rate is observed when volume fraction of Al2O3 particles is varied from 0 to 0.2. The results demonstrate that nanoparticles in water can serve to improve the cooling process of stretching surface which would be beneficial in polymer extrusion processes and coating related applications. (C) 2016 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.