A numerical study of entropy generation, heat and mass transfer in boundary layer flows.
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Date
2018
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Abstract
This study lies at the interface between mathematical modelling of fluid flows and numerical methods
for differential equations. It is an investigation, through modelling techniques, of entropy generation
in Newtonian and non-Newtonian fluid flows with special focus on nanofluids. We seek to
enhance our current understanding of entropy generation mechanisms in fluid flows by investigating
the impact of a range of physical and chemical parameters on entropy generation in fluid flows
under different geometrical settings and various boundary conditions. We therefore seek to analyse
and quantify the contribution of each source of irreversibilities on the total entropy generation.
Nanofluids have gained increasing academic and practical importance with uses in many industrial
and engineering applications. Entropy generation is also a key factor responsible for energy
losses in thermal and engineering systems. Thus minimizing entropy generation is important in
optimizing the thermodynamic performance of engineering systems.
The entropy generation is analysed through modelling the flow of the fluids of interest using systems
of differential equations with high nonlinearity. These equations provide an accurate mathematical
description of the fluid flows with various boundary conditions and in different geometries.
Due to the complexity of the systems, closed form solutions are not available, and so recent spectral
schemes are used to solve the equations. The methods of interest are the spectral relaxation
method, spectral quasilinearization method, spectral local linearization method and the bivariate
spectral quasilinearization method. In using these methods, we also check and confirm various
aspects such as the accuracy, convergence, computational burden and the ease of deployment of
the method. The numerical solutions provide useful insights about the physical and chemical characteristics
of nanofluids. Additionally, the numerical solutions give insights into the sources of
irreversibilities that increases entropy generation and the disorder of the systems leading to energy
loss and thermodynamic imperfection. In Chapters 2 and 3 we investigate entropy generation in
unsteady fluid flows described by partial differential equations. The partial differential equations
are reduced to ordinary differential equations and solved numerically using the spectral quasilinearization
method and the bivariate spectral quasilinearization method. In the subsequent chapters
we study entropy generation in steady fluid flows that are described using ordinary differential
equations. The differential equations are solved numerically using the spectral quasilinearization
and the spectral local linearization methods.
Description
Doctoral Degree. University of KwaZulu-Natal, Pietermaritzburg.