scholarly journals A Review on the Control Parameters of Natural Convection in Different Shaped Cavities with and without Nanofluid

Processes ◽  
2020 ◽  
Vol 8 (9) ◽  
pp. 1011 ◽  
Author(s):  
Sara Rostami ◽  
Saeed Aghakhani ◽  
Ahmad Hajatzadeh Pordanjani ◽  
Masoud Afrand ◽  
Goshtasp Cheraghian ◽  
...  
Keyword(s):  
Porous Media ◽  
Natural Convection ◽  
Free Convection ◽  
Forced Convection ◽  
Opposite Effect ◽  
Fluid Velocity ◽  
Experimental Studies ◽  
Effective Parameters ◽  
Magnetic Forces ◽  
Numerical Studies

Natural convection in cavities is an interesting subject for many researchers. Especially, in recent years, the number of articles written in this regard has grown enormously. This work provides a review of recent natural convection studies. At first, experimental studies were reviewed and, then, numerical studies were examined. Then, the articles were classified based on effective parameters. In each section, numerical studies were examined the parameters added to the cavity such as magnetic forces, fin, porous media and cavity angles. Moreover, studies on non-rectangular cavities were investigated. Free convection in enclosures depends more on the fluid velocity relative to the forced convection, leading to the opposite effect of some parameters that should essentially enhance rate of heat transfer. Nanoparticle addition, magnetic fields, fins, and porous media may increase forced convection. However, they can reduce free convection due to the reduction in fluid velocity. Thus, these parameters need more precision and sometimes need the optimization of effective parameters.

scholarly journals Free and forced convection around line sources of heat and heated cylinders in porous media

2001 ◽  
Vol 427 ◽  
pp. 389-409 ◽  
Author(s):  
VADIM N. KURDYUMOV ◽  
AMABLE LIÑÁN
Keyword(s):  
Porous Media ◽  
Free Convection ◽  
Numerical Solution ◽  
Forced Convection ◽  
Line Source ◽  
Free Stream ◽  
Outer Region ◽  
Circular Cylinders ◽  
Stream Velocity ◽  
Wide Range

An analysis is presented for the steady, two-dimensional, free convection around line sources of heat and heated cylinders in unbounded saturated porous media. It is extended to account also for the effects of forced convection. The study is based on the Boussinesq equations, with the velocities calculated using Darcy's law.The analysis begins with the non-dimensional formulation and numerical solution of the problem of pure free convection around a line source of heat. When this analysis is extended to include the effects of forced convection, two parameters appear in the non-dimensional formulation: the non-dimensional value, V∞, of the free-stream velocity and its angle γ of inclination with respect to the vertical. We first describe the asymptotic form of the solution for large and small values of the distance to the source. The far-field description, which is also applicable to the flow around heated cylinders, is needed to facilitate the numerical solution of the problem. It includes a thermal wake, aligned with the free stream, and an outer irrotational flow with a sink and a vortex at the line source. The temperature distribution near the source involves a constant A0(V∞, γ), to be calculated with the numerical solution of the complete problem, which is used in the evaluation of the heat transfer from heated cylinders when the Rayleigh and Péclet numbers are small compared with unity. In this case we find an inner region where heat conduction is dominant, and an outer region where the cylinder appears as a line source of heat. The asymptotic analysis is complemented with the numerical solution of the general problem for circular cylinders with a wide range of Rayleigh numbers and some representative values of V∞ and γ. We give correlations for the Nusselt number in the limiting cases of pure free convection and pure forced convection.

An Interferometric Study of Mass Transfer From a Vertical Plate at Low Reynolds Numbers

1966 ◽  
Vol 88 (4) ◽  
pp. 399-406 ◽  
Author(s):  
M. M. El-Wakil ◽  
G. E. Myers ◽  
R. J. Schilling
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Boundary Layer ◽  
Mass Transfer ◽  
Natural Convection ◽  
Free Convection ◽  
Forced Convection ◽  
Boundary Layers ◽  
Reynolds Numbers ◽  
Perturbation Solutions

Experimental concentration profiles in steady-state, two-component boundary layers formed by the evaporation of a volatile liquid from a porous vertical flat plate into a heated airstream were obtained by an interferometric technique. Tests were conducted with benzene and n-heptane as the evaporating fluids with airstream temperatures ranging from 70 to 94 F and airstream velocities ranging from 90 to 120 fpm. The Reynolds number range, based on the distance from the leading edge of the plate, was from 75 to 1800. It was experimentally observed that transition from laminar flow occurred at Reynolds numbers between 300 and 600. These values, much lower than generally reported in the literature for heat transfer alone, are believed to be related to the relatively thick boundary layers induced by mass transfer of the heavier-than-air fluid from the plate and the associated free-convection effects. While the flow was primarily forced convection, the experimental data indicated a strong natural-convection effect when compared with analytical predictions based on forced convection alone. This was due primarily to the mass transfer into the boundary layer. An attempt was made to analytically account for the effects of mass transfer and natural convection on the Sherwood-Reynolds numbers relationship by utilizing perturbation solutions for the analogous heat transfer problem. The trends shown by this analysis agreed with the experimental data in the laminar portion of the boundary layer. The absolute magnitudes, however, still differed significantly, showing that first-order perturbation solutions of the mass transfer and free-convection effects are inadequate and pointing to the need for more theoretical work.

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