Nonlinear Flows with Entropy Generation

Abstract

Major interest in this thesis is to analyze entropy generation in hydrodynamic and magnetohydrodynamic flows of viscous and non-Newtonian fluids. Especially the non-Newtonian fluids have pivotal role in many industrial and technological processes such as extrusion of polymers, glass industries, medical equipment, automotive engines, power engineering, oil and food processing industries, aircraft engines, car brake systems, atomizers, turbine engineering and rotational air cleaners etc. In all such processes the flow of fluids, drag forces and transfer of heat is of paramount importance. The rheological characteristics of all the non-Newtonian fluids cannot be determined by a single fundamental equation. Therefore, several models for the study of such fluids have been proposed. In addition, the entropy of system, by second thermodynamics law, consistently increases. Entropy literally measures disorderliness in any system. It is generated by the irreversibility in a process. In all the real-world applications we always need to increase the efficiency of machines by decreasing the irreversibilities in the system. Thus more stress is given here to entropy optimization and Bejan number. Bejan number is employed to determine measure of ratio of thermal irreversibilities to total irreversibilities. Previous information witness that little attention is given to entropy generation in flow of non-Newtonian liquids. We will model problems for flow by stretching sheet and rotating disk. Results of pertinent involved parameters will be shown through graphical interpretations. Skin friction and Nusselt numbers will be discussed. Tabulated values will be used for comparative study of present analysis with previous literatures in limiting cases. This thesis consists of nine chapters Chapter wise detail is given as follows: Chapter one is about some basic definitions and a brief literature survey which provides background and motivation of the present research work. Further, solution procedure is discussed in detail. Chapter two is about nonlinear radiative mixed convective flow with entropy generation minimization rate and heat generation/absorption. A variable thicked stretchable sheet is taken as a source of fluid motion. Heat stretched sheet has nonlinear velocity. Velocity and temperature with respect to different parameters are examined. Entropy generation and Bejan number are sketched and discussed. These contents are published in Physica B: Condensed Matter 538 (2018) 95–103. Chapter three is the extension of chapter two for numerical solution development of power law fluid flow. Flow subject to magnetohydrodynamics (MHD), viscous dissipation and convective conditions is addressed. Solution for governing nonlinear equations is obtained through ND solve technique. Entropy and Bejan numbers are discussed. The obtained results are summarized in the conclusion section. The material of this chapter is accepted for publication in Computer Methods and Programs in Biomedicine https://doi.org/10.1016/j.cmpb.2019.105262. Chapter four generalizes analysis of chapter three. It analyzes the entropy optimization of nonlinear thermal radiative nanofluid flow by a thin needle. Water is taken as a base-fluid having different types of nanomaterials. The resulting ordinary differential equations for the current flow problem are tackled through Shooting technique. Entropy optimization is explored in terms of temperature and velocity gradient. Effects of velocity and temperature through pertinent parameters are shown graphically. The obtained results are concluded in the last section. The contents of this chapter are published in Physica B: Condensed Matter 34 (2018) 113–119. Chapter five reveals the characteristics of entropy optimization in Sisko fluid flow with source/sink and nonlinear radiative heat flux. A rotating stretchable disk is considered as a source of motion for the fluid particles. Fluid characteristics are studied with nonlinear mixed convection, viscous dissipation and Brownian motion. Entropy is computed and shown graphically. Materials of this chapter are published in Journal of the Brazilian Society of Mechanical Sciences and Engineering (2018) 40:373 https://doi.org/10.1007/s40430-018-1288-0. Chapter six is the extension of chapter five. This chapter is about the entropy production in MHD nanofluid flow caused by a rotating disk having variable thickness. Nanofluid flow is studied in presence of Brownian motion and thermophoresis mechanisms. The source for flow is nonlinear stretching of the disk. The obtained problems are transformed through suitable transformations and solved by homotopy analysis method. Convergent solutions are developed Entropy is calculated as a function of velocity and temperature. Graphical results are obtained and discussed. Contents of this chapter are submitted for publication in Physica A. In chapter seven we study the dissipative convective flow of hybrid nanomaterials caused by stretchable disk with entropy optimization. Hybrid nanomaterials are used to increase the thermal properties of the material. Convective conditions are implemented on the disk. Skin friction, heat transfer, entropy minimization and Bejan number are analyzed for engineering interest. Content of this chapter are published in Materials Research Express 6(8) April 2019. Doi.10.1088/2053-1591/ab1b88. In chapter eight, the concept of hybrid nanoparticles flow by a rotating disk is generalized in the presence of MHD and mixed convection. Heat properties are discussed with Joule heating and viscous dissipation. Governing equations are tackled through ND solve technique. Velocity, temperature, heat transfer rate, skin friction, entropy and Bejan number are numerically discussed. Results of this chapters are submitted for publication in Journal of Molecular liquids. Chapter nine is about entropy optimization for non-Newtonian fluid flow with Arrhenius activation energy and binary chemical reaction. Here we analyze the radiative mixed convective flow of Casson nanofluid over a stretching sheet. Heat transfer is with nonlinear thermal radiation, viscous dissipation and heat generation/absorption. Total entropy is calculated. Velocity is studied with uniform magnetic field and nonlinear mixed convection. Brownian motion and thermophoresis are considered. Governing equations are tackled by the built in ND solve technique. Results for velocity, temperature, concentration, entropy and Bejan number are presented. Material of this chapter is published in Physica A: Statistical Mechanics and its Applications, 538, (2020), Article 122806.