Browsing by Author "Mavi, Anele"

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    Computational analysis of viscoelastic fluid dynamics with applications to heat exchangers
    (2019) Mavi, Anele; Chinyoka, Tirivanhu
    In this study, the computational analysis of a pressure driven viscoelastic fluid in a double pipe heat exchanger set-up is investigated. Non-Newtonian viscoelastic fluids in heat exchanger arrangements are encountered in various industrial applications such as power generation, refrigeration and in the food processing industry where the need for cooling and heating of liquids is required. The model problem is governed by complex, non-linear and coupled partial differential equations. These are solved using the semi-implicit finite difference method integrated with the Crank-Nicolson scheme. The pressure-velocity coupling in the momentum equations is resolved by employing the Semi-Implicit Method for Pressure Linked Equations (SIMPLE). To cope with numerical diffusion and numerical stability issues the treatment of convective terms using the upwind schemes is explored. In this work, the behaviour of viscoelastic fluids is rigorously examined by analysing the convective heat transfer from the viscoelastic core fluid of the double pipe heat exchanger to the Newtonian or viscoelastic shell fluid in the outer annulus. In addition, the effects of pressure, momentum, extra stresses, temperature, viscosity and relaxation time on the fluid temperature are investigated; both in the counter flow and parallel flow configurations. Graphical computational results are presented and discussed quantitatively and qualitatively with respect to several parameters involved in the problem.
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    Modelling and Analysis of Viscoelastic and Nanofluid Effects on the Heat Transfer Characteristics in a Double-Pipe Counter-Flow Heat Exchanger
    (2022-05-28) Mavi, Anele; Chinyoka, Tiri; Gill, Andrew
    This study computationally investigates the heat transfer characteristics in a double-pipe counter-flow heat-exchanger. A heated viscoelastic fluid occupies the inner core region, and the outer annulus is filled with a colder Newtonian-Fluid-Based Nanofluid (NFBN). A mathematical model is developed to study the conjugate heat transfer characteristics and heat exchange properties from the hot viscoelastic fluid to the colder NFBN. The mathematical modelling and formulation of the given problem comprises of a system of coupled nonlinear partial differential Equations (PDEs) governing the flow, heat transfer, and stress characteristics. The viscoelastic stress behaviour of the core fluid is modelled via the Giesekus constitutive equations. The mathematical complexity arising from the coupled system of transient and nonlinear PDEs makes them analytically intractable, and hence, a recourse to numerical and computational methodologies is unavoidable. A numerical methodology based on the finite volume methods (FVM) is employed. The FVM algorithms are computationally implemented on the OpenFOAM software platform. The dependence of the field variables, namely the velocity, temperature, pressure, and polymeric stresses on the embedded flow parameters, are explored in detail. In particular, the results illustrate that an increase in the nanoparticle volume-fraction, in the NFBN, leads to enhanced heat-exchange characteristics from the hot core fluid to the colder shell NFBN. Specifically, the results illustrate that the use of NFBN as the coolant fluid leads to enhanced cooling of the hot core-fluid as compared to using an ordinary (nanoparticle free) Newtonian coolant.