Laminar natural convection in a water filled square enclosure containing at its center a horizontal hexagonal cylinder is studied by the lattice Boltzmann method. The hexagonal cylinder is heated while the walls of the cavity are maintained at the same cold temperature. Two orientations are treated, corresponding to two opposite sides of the hexagonal cross-section which are horizontal (case I) or vertical (case II). For each case, the results are presented in terms of streamlines, isotherms, local and average convective heat transfers as a function of the dimensionless size of the hexagonal cylinder cross-section (0.1≤B≤0.4), and the Rayleigh number (103≤Ra≤106).

No abstract

No abstract

The interaction of surface radiation with laminar and turbulent natural convection in differentially heated vertical cavities, filled with air and of large aspect ratio (greater than 10), is analyzed in this study. The k − ωSST turbulence model is used for the formulation of the convection fluid flow and heat transfer, while the governing equations are discretized by the finite-volume method. As an extension of the scarce previous studies, more realistic conditions with a wide range of parameters are considered in the performed simulations. The presented results show the effect of surface radiation on streamlines, isotherms, turbulent kinetic energy, and temperature and vertical velocity profiles, as well as on local and on average convective and radiative heat transfer. Globally, it is found that surface radiation has a weak effect on the dynamic and thermal fields in the major part of the cavity; however, some influence in the upper and lower zones of the cavity is observed. For design purposes, accurate correlations are developed for average convective and radiative Nusselt numbers that cover emissivity of surfaces between 0 and 1, cold wall temperature ranging from 263 K to 303 K, temperature difference between vertical walls ranging from 5 K to 40 K, width of the cavity between 2.5 cm and 7.5 cm, and height of the cavity between 0.25 m and 6 m (this leads to a Rayleigh number ranging from 10 3 to 2 × 10 6 and an aspect ratio between 10 and 80).

No abstract

This study investigates the effect of thermal radiation on natural convection of several water-based nanofluids H2O-(Cu, Al2O3, Ag, TiO2) in a partially heated cubical cavity where the left vertical side is heated by three identical and parallel elements. The right vertical side is totally cooled, and the other ones are kept adiabatic. A developed code based on the finite volume method and the Rosseland approximation is used to solve the governing equations. Calculations were performed for three inclination angles of the rectangular heating elements 0°, 45° and 90°. The effect of governing parameters, namely, Rayleigh number, solid volume fraction, radiation parameter, dimensionless spacing of the three heating elements, their aspect ratio and different type of nanoparticles on the velocity contours, isotherms as well as local and average Nusselt number were considered. The results indicate that the inclination angle has a considerable effect on the dynamic and thermal fields, but its effect on the average heat transfer is insignificant. The total Nusselt number increases with the volume fraction of nanoparticles, the radiation parameter and the aspect ratio of the heated elements. The numerical results also revealed that the Cu and Ag-water nanofluid offer a better heat exchange.

No abstract

No abstract