Unsteady natural convective heat transfer of nanofluids inside a semi-circular cavity under the influence of periodic magnetic field

Abstract

In this thesis, the fundamental concepts of nanofluids and literature survey have been discussed, and two-dimensional time-dependent natural convection flow and heat transfer inside the semi-circular enclosure charged by nanofluid with the presence of the vertically periodic magnetic field has been investigated numerically. Copper-water nanofluid has been taken as default nanofluid. Different types of nanoparticles and base fluids have been considered to examine the better performance of heat transfer. The top circular wall is heated at low-temperature Tc while the bottom diameter is heated at high-temperature Th (Tc < Th). Moreover, different types of thermal boundary conditions are employed along the bottom diameter. The non-linear governing equations with boundary conditions have been transformed into dimensionless forms using a set of non-dimensional variables. The highly powerful partial differential equations solver finite element technique (FEM) of Galerkin weighted residual type has been employed for the numerical simulations in the present problem. The outcomes illustrate an excellent agreement with previously published research. The different physical model parameters such as Hartmann number, Rayleigh number, nanoparticles diameter, nanoparticles volume, size and shape, and Brownian motion of nano-sized particles have been investigated using streamline contours, isothermal lines, and heat transfer rate in terms of average Nusselt number.

The outcomes show that the parameters mentioned above strongly affect the heat transport and flow field within the cavity. It is seen that heat transport rate enhances with the increase of the buoyancy driven parameter Rayleigh number and volume fraction of nanoparticles, decreasing with the higher magnetic effect. The different types of nanofluids have an influential role in heat transport and fluid flow. The heat transport rate increases 22.1% in water-based whereas 5.4% in engine oil-based nanofluid for 1% copper nanoparticles volume. The different thermal boundary conditions have an important impact in heat transport and fluid flow. The uniform thermal condition (case I) gives a better heat transfer rate than others (case II, III, IV, and V). The blade shape nanoparticles provide a higher heat transport rate than spherical, cylindrical, bricks, and platelets. The small size of nanoparticles conforms better heat transfer rate in the resent analysis. The non-uniform magnetic field and its period have a vital role in fluid flow and heat transport. The non-uniform periodic magnetic field provides a higher temperature transport rate than the uniform magnetic field. It is also seen that the average Nusselt number for kerosene-based nanofluid is higher than water-based, ethylene glycol-based, and engine oil-based nanofluids. The heat transport rate is observed at 67.86% for Cobalt (Co)-kerosene whereas 23.78% for Co-water, and 5.68% for Co-engine oil nanofluid with 1% nano-particles volume. In addition, The Brownian motion of nano-sized particles has a significant contribution on heat transfer. The rate of heat transfer increases 28.88% with the Brownian effect, whereas it increases only 3.01% without the Brownian effect. Therefore, the small size of nanoparticles with blade shape and Brownian motion at low Rayleigh number (Ra = 104) provides the best heat transport rate in the case of uniform thermal boundary conditions.