Natural convection of nanofluid in an enclosure with a cylinder

Abstract

This dissertation is performed to investigate the natural convection of nanofluid in an enclosure containing a cylinder. We analyze four problems which are (i) heat transfer characteristics of nanofluids from a sinusoidal corrugated cylinder placed in a square cavity, (ii) magnetohydrodynamic natural convection of a hybrid nanofluid from a sinusoidal wavy cylinder placed in a curve-shaped cavity, (iii) natural convective flow of CuO-water nanofluid in a square-shaped cavity with an inner corrugated circular cylinder embedded in a porous medium and (iv) natural convective non-Newtonian nanofluid flow in a wavy-shaped enclosure with a heated elliptic obstacle. Chapter One provides a concise background and significance of the thesis topic. Clear aims, objectives and relevant literature are stated. It emphasizes the study's importance in advancing existing knowledge and outlines the thesis's structure. In Chapter Two, the flow and heat transfer characteristics of nanofluids confined in a domain bounded by a square and a wavy cylinder are numerically analyzed. The convective phenomena are driven by the higher temperature of the inner corrugated surface. Using super-elliptic functions, the governing equations for the rectangular enclosure are transformed into a system of equations suitable for concentric cylinders. Numerical solutions are obtained with the implicit finite difference method. Parametric results, including streamlines, isotherms, local and average Nusselt numbers, are presented for various scaled parameters such as nanoparticle concentration, Rayleigh number, and aspect ratio. Furthermore, higher nanoparticle concentrations boosted the average Nusselt number at both internal and external cylinders. Notably, the average Nusselt number exhibited enhancement across the entire Rayleigh number range when plotted against the nanofluid's volume fraction. Additionally, correlations have been established for the average Nusselt number at both the inner and outer surfaces of the cylinders, showing excellent agreement with the numerical results. Chapter Three presents a numerical investigation of natural convective flow in a curve-shaped enclosure filled with a hybrid nanofluid containing a wavy-shaped inner cylinder under the influence of a magnetic field. The hybrid nanofluid consists of copper and alumina nanoparticles in a water-based solution. The dimensionless set of the governing equations and associated boundary conditions are numerically simulated using the COMSOL Multiphysics software. Parametric analysis is conducted for the Rayleigh number, nanoparticle concentration, Hartmann number and wave number of the inner cylinder. The results are analyzed in terms of velocity fields, isotherms and local and average Nusselt numbers. The outcomes reveal that increasing the concentration of hybrid nanofluid and Rayleigh number significantly enhances heat transfer rate, while a higher Hartmann number exhibits the opposite effect. Additionally, the number of waves in the inner cylinder influences the intensity of fluid flow and heat transfer inside the enclosure. In Chapter Four, the impact of magnetohydrodynamic forces and nonlinear thermal radiation on natural convection in a square enclosure with an inner corrugated circular cylinder is investigated. The study considers a nanofluid composed of copper oxide and water, diffused throughout the porous medium of the enclosure. The numerical solution for this chapter is obtained using the COMSOL Multiphysics software. The nanofluid's temperature and nanoparticle volume concentration both have an effect on determining the dynamic viscosity and thermal conductivity. Computational results reveal the influence of various parameters, such as Rayleigh number, Darcy number, Hartmann number, surface temperature parameter, radiation parameter and solid volume concentration of nanoparticles, on flow and thermal patterns inside the enclosure. Heat transfer rates are estimated based on the local and average Nusselt number. The study highlights that intensifying Rayleigh number, radiation, surface temperature and nanoparticle concentration enhance fluid flow intensity, while an ascending Hartmann number counteracts this effect. Moreover, filling the enclosure with a porous substance significantly reduces the heat transfer rate. Chapter Five deals with the natural convection of non-Newtonian nanofluid flow and heat transfer in a wavy-shaped enclosure with an elliptical inner cylinder, considering the effect of an inclined magnetic field. The dimensionless governing equations are simulated using the COMSOL Multiphysics software. The dynamic viscosity and thermal conductivity of the nanofluid, influenced by temperature and nanoparticle volume fraction, are taken into account. Numerical analysis explores varying Rayleigh number, Hartmann number, magnetic field inclination angle, rotation angle of the inner cylinder, power-law index and nanoparticle volume fraction. Findings indicate that higher nanoparticle volume fractions reduce fluid movement and heat transfer rates. Rayleigh number enhances flow strength, resulting in improved heat transfer. A higher Hartmann number diminishes fluid flow, while magnetic field inclination angle exhibits converse behavior. Maximum average Nusselt number values occur at a magnetic field inclination angle of 90. The power-law index significantly affects heat transfer, with shear-thinning liquids augmenting the average Nusselt number. Finally, the conclusions and future works are provided in chapter Six.