Computational modelling and entropy generation analysis of nanofluids in a channel

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Nelson Mandela African Institution of Science and Technology


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.




Computational modelling, Entropy generation, Fluids, Energy, Nanofluids