No abstract

In this paper, the scenario leading to chaos in natural convection of Cu-water nanofluid inside an inclined square enclosure with the aspect ratio equal to unity is numerically investigated. The enclosure is heated from one part of the side and cooled through two other opposite half sides. The governing equations and the corresponding boundary conditions are solved numerically using the finite difference method. The effect of Rayleigh number and the volume fraction on natural convection flow are analyzed. The obtained results indicate that the mode of fluid flow which is initially stationary, passes by a periodic mode across a supercritical Hopf bifurcation, then quasi periodic at two incommensurable frequencies, before reaching the final stage of chaotic convection for both pure fluid and nanofluid. The sequences of bifurcation are presented graphically; it was found that the presence of suspended nanoparticles inside the base fluid causes significantly the delay of this transition.

No abstract

Stability and transition problems of two dimensional laminar external flow over a flat plate with wall suction and blowing are studied numerically using the temporal linear stability theory. The flow is assumed similar two-dimensional laminar boundary-layer. The mean velocity profiles are obtained numerically for the case of suction or blowing. The stability equation is given in a general form which can be applied to Chebyshev domain and in boundary layer domain and solved numerically by the Chebyshev collocation spectral method. The neutral stability curves and the critical Reynolds numbers are presented.

Immersion of fins in latent heat thermal energy storage systems has been used as an influential approach to remedy the poor thermal conductivity of phase-change materials. Present paper numerically investigates heat transfer and phase change improvement by means of longitudinal fins in a shell and tube thermal energy storage unit. The main aim of this study is to investigate the effect of fin orientation on the performance of the storage unit. Six configurations of different fin numbers (2, 4 and 8 fins) and orientations (π/2, π/4, and π/8) are tested. For simulations, a 2D mathematical model incorporating the enthalpy-porosity method and finite volume techniques are established and solved by ANSYS-Fluent. The numerical predictions are successfully validated by comparison with experimental and numerical data from the literature. Heat transfer characteristics and melting process are analyzed through streamlines, isotherms, mean temperature, heat flux and heat transfer coefficient as well as transient melting front position and liquid fractions. Results show that orientation of fins has significant impact on the charging time for two cases (2 and 4 fins) whereas no significant reduction in charging time was obtained for the case of 8 fins. In case of utilizing 2 fins, a fin orientation of 0° (vertical fins) shortens the charging time by up to 2.5 folds compared to the horizontal fins (90°). These results could help designing efficient latent thermal energy storage units.