Vertical cylinders, natural convection

Natural Convection over Surfaces 510 Vertical Plates (Fj = constant) 512 Verbeal Plates (4 = constant) 512 Vertical Cylinders 512 Inclined Plates 512 Horizontal Plates 513 Horizontal Cylinders and Spheres 513... 

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... 

C Under what conditions can the outer surface of a vertical cylinder be treated as a vertical plate in natural convection calculations ... 

For the heated vertical plate and horizontal cylinder, the flow results from natural convection. The stagnation configuration is a forced flow. In each case the flow is of the boimdai7 Kiyer type. Simple analytical solutions can be obtained when the thickness of the du.st-free space is much smaller than that of the boundary layer. In this case the gas velocity distribution can be approximated by the first term in an expansion in the distance norroal to the surface. Expressions for the thickness of the dust-free space for a heated vertical surface and a plane stagnation flow are derived below. 

FIGURE 4.14 Definition sketch for natural convection from long vertical cylinders. 

Discussion of Correlation for Specific Shapes. The equation for elliptical cylinders fits the approximate analysis of Raithby and Hollands [224] but has not been verified by experiment except in the limiting cases of a vertical plate (C/L = 0) and a circular cylinder (C/L = 1.0). The vertical plate predictions by Eq. 4.48 are slightly different than those based on the more accurate specialized equations given in the section on external natural convection in flat plates. 

Circular Isothermal Fins on a Horizontal Tube. Tsubouchi and Masuda [269] measured the heat transfer by natural convection in air from circular fins attached to circular tubes, as in the configuration shown in Fig. 4.23/ Correlations for the heat transfer from the tips of the fins (see the figure for definition), and from the cylinder plus vertical fin surfaces, were reported separately. 

Horizontal Cylinders. For a heated horizontal cylinder in perpendicular cross flow, the angle of the approaching stream, ( > in Fig. 4.47, greatly affects the heat flow in the mixed convection regime. For ( > = 0 the forced flow assists the natural convection and the dependence of the average Nus-selt number on Re resembles path A in Fig. 4.44. For = 90° there is a sharper transition from natural to forced convection than when 4> = 0, while for opposed flow (( > = 180°) there is a minimum as shown by path B in Fig. 4.44. For a cooled cylinder the same description applies except that ( > is measured from the vertical axis extending upward from the cylinder. 

T. Fujii and M. Fujii, Experiments on Natural Convection Heat Transfer from the Outer Surface of a Vertical Cylinder to liquids, Int. J. Heat Mass Transfer (13) 753-787,1970. 

C. F. Hess and C. W. Miller, Natural Convection in a Vertical Cylinder Subject to Constant Heat Flux, Int. J. Heat Mass Transfer (22) 421-430,1979. 

R. J. Kee, C. S. Landram, and J. C. Miles, Natural Convection of a Heat Generating Fluid Within Closed Vertical Cylinders and Spheres, J. Heat Transfer (98) 55-61,1976. 

W. J. Minkowycz and E. M. Sparrow, Local Nonsimilar Solutions for Natural Convection on a Vertical Cylinder, / Heat Transfer (96) 178-183,1974. 

W. Murgatroyd and A. Watson, An Experimental Investigation of the Natural Convection of a Heat Generating Fluid Within a Closed Vertical Cylinder, /. Mech. Eng. Sci. (12) 354-363,1970. 

E. M. Sparrow and M. Charmichi, Natural Convection Experiments in an Enclosure Between Eccentric or Concentric Vertical Cylinders of Different Height and Diameter, Int. J. Heat Mass Transfer (26/1) 133-143,1983. 

Natural convection from vertical planes and cylinders. For an isothermal vertical surface or plate with height L less than 1 m (P3), the average natural convection heat-transfer coefficient can be expressed by the following general equation ... 

Simplified equations for the natural convection heat transfer from air to vertical planes and cylinders at 1 atm abs pressure are given in Table 4.7-2/-In SI units the equation for the range of Nq, Np, of lO to 10 is the one usually encountered and this holds for (L AT) values below about 4.7 m K and film temperatures between 255 and 533 K. To correct the value of h to pressures other than 1 atm, the values of h in Table... 

Losses by Natural Convection from a Cylinder. A vertical cylinder 76.2 mm in... 

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