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Abstract: This paper investigates the behaviour of two non-mixing fluids flowing in a heated curved channel. In simulating this immiscible fluid flow, a multi-phase model based on VOF approach is developed for steady, turbulent, incompressible fluid flow through curved channel. The analysis examines the influence of centrifugal forces arising from channel curvature on the phase distribution and flow patterns, and their impact on the thermal characteristics. Unique flow features are identified through the interactions between the fluid phases and vortex structures of the immiscible flow in curved channels. The convective heat transfer in curved channel is appraised in relation to the behaviour of fluid components and curved channel flow parameters. Finally, the study presents a Second-Law irreversibility analysis whereby a thermal optimisation technique is developed for immiscible fluid flow through heated curved channels. [Copyright &y& Elsevier]

Fluid flow through curved ducts is essentially characterised by the secondary flow effects due to duct curvature and cross-sectional flow geometry. Such flows produce vortex structures making the fluid behaviour vastly different than those in straight ducts while intrinsically promoting forced convection through fluid mixing. Examining the unique features of secondary flow and wall heat transfer, this paper presents a numerical simulation on the fluid flow through curved elliptical ducts, including circular geometry. The study develops and validates a novel numerical model based on three-dimensional vortex structures (helicity) and a curvilinear mesh system to overcome previous modelling limitations. Considering several duct aspect ratios, flow rates and wall heat fluxes, computations are performed to obtain the flow patterns and thermal characteristics. Parametric influences on flow features and forced convection are described through physical interpretation. The onset of vortices due to secondary flow instability is carefully examined in relation to the duct aspect ratio and flow rate. Appraising their merits, two techniques are developed for accurate detection of secondary flow instability and integrated into the computational process, which was not previously feasible. An approach based on the Second Law irreversibility is evaluated for thermal optimisation of fluid flow through curved elliptical ducts. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents a numerical investigation for examining the secondary vortex motion and associated heat transfer process in fluid flow through curved passages. Overcoming current modelling limitations, the study formulates an improved simulation model based on 3-dimensional vortex structures for describing secondary flow and its thermal characteristics. For developing laminar fluid flow through curved rectangular ducts, the analysis performs a detailed parametric study involving the contours of helicity and outer duct wall pressure gradient for a range of flow rates, duct aspect ratios, duct flow curvatures and external wall heat fluxes. The flow conditions leading to hydrodynamic instability and Dean vortex generation in curved passages are carefully analysed, identifying the flow and geometrical parametric influences. Active interaction of buoyancy force on fluid motion arising from wall heating is considered where aspects of boundary layer separation is used in recognising thermal enhancement due to secondary flow. The simulated results are validated with the available experimental data. Surpassing precision and reliability of current practise, the study develops two numerical approaches offering improved capabilities for capturing the onset of hydrodynamic instability and resulting Dean vortices. These techniques are compared and assessed for their merits of application in determining the onset of secondary flow hydrodynamic instability with and without external wall heating. [Copyright &y& Elsevier]

A numerical simulation is presented to describe the secondary flow characteristics in the flow through curved rectangular ducts that are heated on the outer (concave) wall. The buoyancy body forces due to external heating are incorporated in the formulation. The governing equations of momentum, mass continuity and energy of the flow are non-dimensionalised and transformed into vorticity-streamfunction. The equations are discretised using a finite volume method and the dynamical variables are defined on a staggered grid. The resulting penta-diagonal system of linear algebraic equations is solved using the Strongly-Implicit-Procedure. Numerical computations are performed for the flow through rectangular ducts of aspect ratios 1 to 8 and for the Dean number lying in the range 20 to 500. The external wall heat fluxes of 0 to 200 W·m−2 are considered. The computation accurately captures the influence of external heating on the secondary vortex motion and, predicts the occurrence of Dean vortices in non-isothermal flow through the curved ducts. With wall heating, the flow pattern rapidly deviate from the symmetrical vortex motion observed under isothermal conditions. The formation of Dean vortices still takes place in the flow although it is postponed to higher flow rates where the flow symmetry is gradually re-established. The number of Dean vortices formed in the flow is strongly influenced by the aspect ratio of ducts. Convective heat transfer is significantly enhanced by the secondary flow particularly when the Dean vortices emerge at the outer wall. The predicted characteristics of secondary flow and heat transfer conform to and agree well with the available experimental data. [Copyright &y& Elsevier]