Computational modelling and entropy generation analysis of nanofluids in a channel
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Date
2016
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Publisher
Nelson Mandela African Institution of Science and Technology
Abstract
Nanofluid is a fluid containing nanometre- sized particles, called nanoparticles. These fluids
are engineered colloidal suspension nanoparticles in a based fluid. The commonly used fluids
are water, ethylene, oil and lubricant. Entropy is an extensive thermodynamic property that is
the measure of a system’s thermal energy per unit temperature that is unavailable for doing
useful work. That is it destroys the available energy in any flow process and thermal system.
This study consists of six chapters. Chapter one is an introduction, in this chapter useful
terms have been defined, objectives of the study, statement of the problem, significance of
the study ware stated. The method used for analysis in all chapters is a semi discretization
finite difference method together with Runge-Kutta Fehlberg integration scheme. The
nanoparticles used was Copper (Cu) and Alumina (AI2O3).
In chapter two, the analysis of the entropy generation in a variable viscosity channel flow of
nanofluids with convective cooling was numerically investigated. The results revelled that
Entropy generation rate generally increases with time /, Eckert number Ec, viscosity variation
parameter /?, pressure gradient A, thermophoresis parameter Nt. Increase in Biot Bi increase
entropy generation at the walls but decreases entropy generation within the channel. The
paper was prepared and published in Comptes Rendus Mecanique.
In chapter three, the combined effect of buoyancy force and convective cooling on the
unsteady flow, heat transfer and entropy generation rate in water based nanofluids was
investigated. A^Oj-water nanofluid observed to produces higher entropy than Cu-water
nanofluid. Fluid friction irreversibility dominants the channel centreline region while the
effects of heat transfer irreversibility near the walls increases with Grashof number Gr, Ec, A,
but decreases with nanoparticles volume fraction <p and Bi. Prepared paper was published in
applied and computational mathematics journal.
In chapter four, the flow structure, heat transfer and entropy generation in unsteady
generalized Couette flow of a water-based nanofluid with convective cooling was
numerically investigated. It was found that the entropy generation increases with (p and Ec, it
decreases with J. With an increase in Bi the entropy generation rate decreases and reverse its
behaviour near the upper wall. The Bejan number increases with an increase in^. One paper from this chapter was prepared and published in Sadhana - Academy Proceedings
in Engineering Science.
In chapter five, computational model and thermodynamic analysis of the effects of Navier
slip and wall permeability on entropy generation in unsteady generalized Couette flow was
investigated. An increase in an entropy generation rate was observed with an increase in^
and slip parameter f , the paper was published at University Politehnica of Bucharest (U.P.B)
Scientific Bulletin, Series D. Chapter six consist of general discussion, conclusion,
recommendation and future work.
General observation was that entropy can be reduced by mixture of nanoparticles and base
fluid with careful combination of parameters controlling the flow and geometry in
consideration. Alumina- water nanofluid produces more entropy compared to Copper- water
nanofluid.
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Thesis
Keywords
Computational modelling, Entropy generation, Fluids, Energy, Nanofluids