Form view factor

Form view factor A factor which describes the effects of the relative area of two surfaces, the geometry of the surfaces in relation to each other, and the two emissivities on radiation heat exchange between the surfaces. 

Many literature sources document closed-form algebraic expressions for view factors. Particularly comprehensive references include the compendia by Modest (op. cit., App. D) and Siegel and Howell (op. cit., App. C). The appendices for both of these textbooks also provide a wealth of resource information for radiative transfer. Appendix F of Modest, e.g., references an extensive listing of Fortan computer codes for a variety of radiation calculations which include view factors. These codes are archived in the dedicated Internet web site maintained by the ublisher. The textbook by Siegel and Howell also includes an extensive atabase of view factors archived on a CD-ROM and includes a reference to an author-maintained Internet web site. Other historical sources for view factors include Hottel and Sarofim (op. cit., Chap. 2) and Hamilton and Morgan (NACA-TN 2836, December 1952). 

The second conversion of GS to (GSi)j will be Case 4 of Table 5-10, the two-surface-zone enclosure with computation simphfied by assuming that the direct-view factor from any spot to a surface equals the fraction of the whole enclosure that the surface occupies (the speckled-furnace model). This case can be considered an idealization of many processing furnaces such as distilling and cracking coil furnaces, with parts of the enclosure tube-covered and part left refractory. (But the refractory under the tubes is not to be classified as part of the refractory zone.) Again, one starts with substitution into Eq. (5-173) of the terms GSi, CS and S Si from Table 5-10, Case 4, with all terms first converted to their grayqrfus-clear form. To indicate the procedure, one of the components, S Si, wil be formulated. 

View factors for hundreds of common geometries are evaluated and the results are given in analytical, graphical, and tabular form in several publica-tion.s. View factors for selected geometries are given in Tables 13-1 and 13-2 in analytical form and in Figs. 13-5 to 13-8 in graphical form. The view... 

Determine the view factors associated with an enclosure formed by two concentric spheres, shown in Fig, 13 10. 

This important result is applicable to any two gray, diffuse, and opaque surfaces that-fqrm an enclosure. The view factor f 2 depends on the geometry and must hj "determined first. Simplified forms ofRq. 13-36 for some familiar arrangements that fonn a two-surface enclosure are given in Table 13-3. Note that f, 2 = I for of these special cases. 

A further relationship between view factors can be found when n areas, for each of which L = const holds, form an enclosure such as that illustrated schematically in Fig. 5.51. From the radiation balance for area i,... 

A simple example for the application of the relationships (5.132) and (5.133) is provided by radiation in an enclosure formed by two spherical surfaces 1 and 2, Fig. 5.52. There are four view factors in this case, l) i. fqo, Toi and F22 The summation rule is applied to the inner sphere in order to calculate them ... 

Before we set up the equation system for the radiosities of the four zones we will calculate the 16 view factors Fij. Obviously Fu = F22 = 0 the view factor F12 = 0.1230 is carried over from Example 5.9. In order to determine the other view factors the auxiliary area 5 in Fig. 5.65 with the dashed line is introduced. With z = 2 + (h/2r)2 = 3.5625, F15 is calculated from the equation given in Example 5.9 as F15 = 0.3072. For the enclosure formed by 1, 3 and 5 we have Fjs + Eis = E from which Fjs = 0.6928. The summation for the entire cylinder is... 

Sheinkcr and his co-workers have used ultraviolet and infrared spectroscopic data to show that the imino form of benzenesul-fonamido derivatives of thiazoles and l-thia-3,4-diazoIes is preferred to the amino form by a large factor. In view of this work, the formulation of 2-aryIsulfonamidooxazoles in the amino form on the basis of chemical evidence must be regarded with caution. 

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