Numerical Investigation of Natural Convection Around Isothermal Horizontal Rectangular Ducts

Abstract

Two-dimensional laminar natural-convection heat transfer in air around horizontal ducts with rectangular and square cross sections is studied numerically. Different aspect ratios are used for wide ranges of Rayleigh numbers. Results are presented in the form of streamlines and isothermal plots around the circumference of the ducts. The computational procedure is based on the finite-element technique. Temperature and velocity profiles are obtained near each surface of the ducts. Reverse flow and circulations are observed at high aspect ratios. Heat transfer data are generated and presented in terms of Nusselt number versus Rayleigh number for different aspect ratios. Correlation covering the aspect ratios used is obtained in dimensionless form of Nusselt number, Rayleigh number, and aspect ratio.

Laminar natural convection from a heated square cylinder immersed in power-law liquids

“…Table 3 reports a comparison between the literature and present numerical results for scores of values of the Rayleigh number. The present values are within 3% of those of Chang et al [29] and 7% of that of Zeitoun and Ali [30]. It needs to be emphasized here that deviations of this order are not at all uncommon in such numerical studies and are generally attributed to domain and grid effects, solution methodology (finite difference/finite element/finite volume, for instance), convergence criterion, etc.…”

“…As noted earlier, limited prior numerical results are available on free convection heat transfer from a heated horizontal square cylinder in stagnant air [27,30]. Table 3 reports a comparison between the literature and present numerical results for scores of values of the Rayleigh number.…”

“…Naturally, the gradients (velocity and temperature) are expected to be steep near the immersed cylinder which gradually decrease away from the bluff body. It therefore stands to reason that a fine mesh is needed near the bluff body and one can Table 3 Comparison between the present and literature [29,30] achieve computational economy by using a relatively coarse mesh away from the cylinder. This objective was achieved by dividing the computational domain into two sub-sections: the first region close to the cylinder extends up to a distance of 4D radius in all directions as shown schematically in Fig.…”

“…The resulting values of the Nusselt number were found to be in agreement with the available experimental data. More recently, Zeitoun and Ali [30] have numerically investigated free convection from heated two-dimensional cylinders of Other than these studies dealing with the natural convection in an unconfined expanse of fluid (mostly air), few studies are also available on confined square cylinders. For instance, De and Dalal [31] numerically investigated free convection from a heated square cylinder (rotated by 45°) situated at the centre of an adiabatic square enclosure filled with air.…”

Numerical study of forced convection around heated horizontal triangular ducts

“…This process is repeated until the residuals of all equations are negligible. A similar routine is used by Al-Sanea and Ali [19] and by Kiwan and Ali [20] to obtain the heat transfer and flow fields near the extrusion slit of a continuously moving surface in plain and porous medium respectively, also by Zietoun and Ali [21] for natural convection over horizontal rectangular ducts in air. As shown in Fig.…”