Document vBK99OxEjGbnyJZOgb06RRZ36

328 Chapter 17 1945 Guide Table 7> Areas of FLanged Fittings, Square Feet t' f . Pipe Insulation 329 Nominal Pips Size * (Inches) i m 2 2K 3 3M 4 4)4 5 6 8 10 12 Flanged Coupling 90 Deg Ell Long Radius Rn. Tee Cbosb Standard Extra Heavy Standard Extra Heavy Standard Extra" Heavy Standard Extra Heavy Standard Extra Heavy 0:320 0.383 0.477 0.672 0.841 0.945 1.122 1.344 1.474 1.622 1.82 2.41 3.43 4.41 0.438 0.795 1.015 0.892 1.083 1.235 1.575 1.622 2.07 0.510 0.957 1.098 1.084 1.340 1.481 1.925 1.943 2.53 0.727 1.174 1.332 1.337 1.874 1.815 2.68 2.38 3.54 0.848 1.65 2.01 1.84 2.16 2.54 3.09 3.32 4.06 1.107 2.09 2.57 2.32 2.76 3.21 4.05 4.19 5.17 1.484 2.38 3.49 2.68 3.74 3.66 5.33 4.77 6.95 1.644 2.98 3.96 3.28 4.28 4.48 6.04 5.83 7.89 L914 3.53 4.64 3.96 4.99 5.41 7.07 7.03 9.24 2.04 3.95 5.02 4.43 5.46 6.07 7.72 7.87 10.07 2.18 4.44 5.47 5.00 6.02 6.81 8.52 8.82 10.97 2.78 5.13 6.99 5.99 7.76 7.84 10.64 10.08 13.75 3.77 6.98 9.76 8.56 11.09 10.55 14.74 13.44 18.97 5.20 10.18 13.58 12.35 15.60 15.41 20.41 19.58 26.26 6.71 13.08 17.73 16.35 18.76 19.67 26.65 24.87 34.11 Including areas of accompanying flanges bolted to the fitting. insulations given in Table 8 can be obtained by multiplying the losses obtained from Figs. 1, 2, or 3 by the factors given in Table 9. Pipes operating at high temperatures are frequently insulated to the best advantage by combining a high temperature insulation near the pipe with a moderate or low temperature insulation around it as an outer layer. By this method an efficient material may be used for each of the two temperature ranges encountered. In calculating the heat loss through such a combination the mean temperature of each layer must be determined along with the thickness of each. This is readily done in three or four calculations performed as a series of approximations in which assumptions of thickness and mean temperature are adjusted as indicated. The rate of heat loss from a surface maintained at constant temperature is greatly increased by air circulation over the surface. In the case of well-insulated surfaces, the increases in losses due to air velocity are very small as compared with increases from bare surfaces, because of the fact Table 8. Thermal Conductivity (k) of Various Type Pipe Insulations for Medium and High Temperature Pipe1 Expressed in Btu per {hour) {square foot) {degree Fahrenheit temperature difference per inch) Types of Insulating Materials Density Lb/C u- Ft Temp. Range of Accepted Use Mean Temperature, Deg F 100 200 300 400 500 13-15 Up to 600 F 0.41 0.45 0.48 0.52 Corrugated Asbestos--Type 11-13 Up to 300 F 0.57 0.68 0.80 Laminated Asbestos--Type (35-40 laminations per 1 in.)__ 15-17 18-20 30-35 Up to 300 F 0.51 0.59 0.69 Up to 300 F 0.49 0.57 0.65 Up to 700 F 0.39 0.44 0.49 0.54 .... Fig. 1. Heat Loss Through 1 In. Thick 85 per cent Magnesia Type Covering 10-15 25-30 Brown Asbestos Fiber--Type...... 13-15 Up to 800 F 0.40 0.45 0.50 0.55 Up to 1900 F 0.63 0.66 0.69 0.72 0.75 Up to 1200 F 0.34 0.39 0.44 0.49 0.54 a^,air flowing over the surface of the insulation can increase only the"ductance of heat from surface to air, and cannot change the internal nauctance of the insulation itself. The maximum increase in heat loss Average values from various laboratories for insulating materials of various manufacturers. :p /* e to air velocity ranges from about 15 per cent in the case of 1-in. thick i i !