Entropy Generation Effects During Flow And Heat Transfer Processes

Abstract

Entropy is a useful, measurable quantity which is widely used in the field of fluid mechanics and heat transfer to study the energy losses that cannot be reversed. Entropy based analysis of flow and heat transfer phenomena helps to identify the factors that are responsible for the entropy production. Knowing about the causes of entropy generation is essential because large amount of irreversible energy losses do affect the efficiency of thermo-mechanical devices in practical applications. In this dissertation, entropy generation effects have been inspected in the boundary layer flow and heat transfer of viscous fluid due to stretching surfaces. Different geometrical configurations of flat and curved stretchable sheets as well as channels with stretching walls have been considered and the effects of presence of magnetic field, porous medium and slip effects on entropy production are examined. The problems have been investigated theoretically by using appropriate models that are derived from the laws v i of conservation of mass, momentum and energy. Moreover, second law of thermodynamics is applied for the examination of entropy generation in the considered thermal processes. Analytical and numerical methods have been employed to obtain the solutions of the governing nonlinear equations. Homotopy Analysis Method (HAM) has been used to obtain the analytic solution and shooting technique has been utilized for the numerical computations. The accuracy and validity of the obtained analytical and numerical solutions have been proved by comparing them with available results under limiting conditions or by comparing the analytical and numerical values with each other. The studies carried out in this thesis reveal that entropy generation effects are more significant near the stretching surfaces. Furthermore, the magnetic field is also a strong source of entropy production. The viscous dissipation effects are also observed to be responsible for entropy generation. It is also noted that the entropy generation is more pronounced in the case of curved stretching surface.