Rectangular enclosures vertical

Attention will here be restricted here to flow in a rectangular enclosure as shown in Fig. 8.24. In general, the enclosure is inclined to the vertical as illustrated in Fig. 8.24. For simplicity, in order to illustrate how enclosure flows can be analyzed, it will be assumed that one wall of the enclosure (AB in Fig. 8.24) is at a uniform high temperature, Th, and that the opposite wall (CD in Fig. 8.24) is at a uniform low temperature, Tc Two boundary conditions on temperature are usually considered on the two remaining end walls (BC and DA in Fig. 8.24). If these walls are made from a material that has a low thermal conductivity, it is usual to assume that these walls are adiabatic, i.e., that there is no net heat transfer to or from the wall at any point on the wall. Alternatively, if these walls are made from a material that has a relatively high thermal conductivity, it is usual to assume that these walls are perfectly conducting and that the temperature on these end walls varies linearly with distance from the hot wall from T to Tc-... 

Some of the more commonly used methods of obtaining solutions to problems involving natural convective flow have been discussed in this chapter. Attention has been given to laminar natural convective flows over the outside of bodies, to laminar natural convection through vertical open-ended channels, to laminar natural convection in a rectangular enclosure, and to turbulent natural convective boundary layer flow. Solutions to the boundary layer forms of the governing equations and to the full governing equations have been discussed. 

Rubel, A. and Landis, R., Numerical Study of Natural Convection in a Vertical Rectangular Enclosure , Phys. Fluids, Suppl. II, Vol. 12-11, pp. 208-213, 1969. 

Mass How Rate ttirougn ttie Space beLV, een Plates 519 9-5 Natural Convection Inside Enclosures 521 effective Thermal Conductivity 522 Horizontal Rectangular Enclosures 523 Inclined Rectangular Enclosures 523 Vertical Rectangular Enclosures 524 Concentric Cylinders 524 Concentric Spheres 525 Combined Natural Convection and Radiation 525... 

Enclosures arc frequently encountered in practice, and heal transfer through them is of practical interest. Heat transfer in enclosed spaces is complicated by the fact that the fluid in the enclosure, in general, does not remain stationary. In a vertical enclosure, the fluid adjacent to the hotter surface rises and the fluid adjacent to the cooler one falls, setting off a rolationary motion within the enclosure that enhances heat transfer through the enclo.surc. Typical flow patterns in vertical and horizontal rectangular enclosures are shown in Figs. 9-21 and 9-22. 

FIGURE 9-21 Convective currents in a vertical rectangular enclosure. 

A vertical rectangular enclosure with isothermal surfaces. 

Let us now analyze the more complex shielding application of Figure 7.12(a), which illustrates a rectangular enclosure partitioned by two equal horizontal PEC walls. In the front plane, there is a centered (20 x 5) cm horizontal aperture. The dimensions are a = b = 60 cm, d = 120 cm, / = 70 cm, w = 2 cm, and the excitation is launched by a vertical coaxially fed monopole. Due to the nonstandard operators of (3.43), the domain is discretized into the coarse grid of30 x 60 x 30 cells with Ax = Ay = Az = 2 cm and At = 30.567 ps. In the area of the aperture, spatial derivatives are computed by the fictitious-point technique of Section 2.4.5, whereas the DRP schemes of Section 2.5.3 are also utilized. Figure 7.12(b) displays the shielding efficiency defined as the ratio of the electric field amplitude evaluated in front of... 

Attention will here be restricted to two-dimensional steady flow in a rectangular porous medium -filled enclosure which is, in general, inclined at an angle to the vertical. One wall of the enclosure is kept at a uniform high temperature and the opposite wall is kept at a uniform low temperature. The o her two walls of the enclosure are assumed to be adiabatic, i.e., it is assumed that no heat is transferred into or out of these walls. The situation is, therefore, as shown in Fig. 10.27. 

The bed-to-surface heat transfer coefficient (about 85 280 W/m °C) by solids convection and radiation is lower in circulating bed AFBC than in bubbling bed AFBC due to the lower bed density and vertical heat transfer surface orientation, and the heat transfer coefficient decreases with increased height. The dilute zone of the furnace is water-walled, with the heat transfer surfaces placed at the perimeter of the rectangular vessel enclosure. Additional vertical heat transfer surface walls or wing walls may be hung within the vessel to increase its heat removal capacity. Another means to increase the heat transfer surface is to place an exter-... 

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