Document QJ5RNdJkVDR1vOLeop5nxp36L

456 CHAPTER 32 1959 Guide Table 2 .... Heat Losses from Horizontal Bare Steei ripe* and Fiat Surfaces (a &fu per (Sq Ft of Pipe Surface) (Hour) (F Deg Temperature Difference Between Pipe and Air) Pip* linear Temperature Difference F Deg Between Pipe Surface end Surrounding Air. Air at 80 F. bdMi 50 too 150 200 250 300 350 400 450 500 550 600 650 700 750 600 850 900 950 1000 H 0.220 2 1? 2.48 2 80 3.10 3.42 3 74 4.07 4.47 4.86 5.28 5.72 6.19 6.69 7.22 7.79 8.39 9.03 9.70 10.42 11.18 0.275 2.08 2.43 2.74 3.04 3 35 3.67 4.00 4.40 4.79 5.21 5.65 6.12 6.61 7.15 7.71 8.31 8.95 9.62 10.34 LI.09 0.344 2.04 2.38 2.69 2.99 3.30 3,61 3.94 4.33 4.72 5.14 5.58 .6.05 6.64 7.07 7.64 8.23 8.87 9.55 10.26 11.02 IK 0.435 2.00 2.34 2.64 2.93 3.24 3.55 3.88 4.27 4.66 5.07 5.51 6.97 6.47 V.UU 7.56 8.16 8.79 9.47 10.18 10.94 1$ 0.497 1.98 2.31 2.61 2.90 3.20 3.52 3.84 4.23 4.62 5.03 5.47 5.93 6.43 6.96 7.52 8.12 8-75 9.43 10.14 10.89 2 0.622 1.95 2.27 2 56 2 85 3.15 3.46 3-78 4.17 4.66 4.97 5.41 5.87 6.37 6.89 7.45 8. as 8.68 9.36 10.07 10.82 2K 0.753 1.92 2.23 2.52 2.81 3.11 3,42 3.74 4.12 4.51 4.92 5.36 5.82 6.31 6.84 7.40 7.99 8.63 9.30 10.01 io. V? 3 0.916 1.89 2.20 2.49 2.77 3.07 3.37 3.69 4.08 4.46 4.8"/ 5.31 5.77 6.26 6.79 7.35 7.94 8:57 9.25 9.96 10.71 3X 1.047 1.87 2.18 2.46 2.74 3.04 3.34 3.66 4.as 4.43 4.84 5.27 5.73 6.23 6.75 7.31 7.91 8.54 9.21 9.92 10.67 1.85 2.16 2.44 2.72 3.01 3.32 3.64 4.02 4.40 4.81 6.25 5.71 6.20 6.72 7.28 l, 87 8.51 9.18 9.89 10.64 4K 1.309 1.84 2.14 2.42 2 70 2.99 3.30 3.61 4.00 4.38 4.79 5.22 5.68 6.17 6.69 7.25 7.85 8.48 9.15 9.86 10.61 5 1.456 1-83 2.13 2.40 2.68 2.97 3.28 3.59 3.97 4.35 4.76 5.20 5.65 6.15 6.68 7.23 7.82 8.45 9.12 9.83 10.58 1.734 1.80 2.10 2.37 2.65 2.94 3.24 3.55 3.94 4.32 4.72 5.16 5.61 6.10 6.63 7.19 7 78 8.41 9 08 9.79 10.54 7 1.996 1.79 2.08 2.35 2.63 2.91 3.21 3.52 3.91 4.29 4.69 5.13 5.58 6.07 6.6C 7.15 7.75 8.38 9.05 9.76 10.5J 8 2.258 1 77 2.06 2.32 2 60 2.89 3.19 3.50 3.88 4.20 4.67 5.10 5.50 6 as 6.57 7.12 7.72 8.35 9.02 9.73 10.48 0 2.520 1.76 2.05 2.31 2.59 2.87 3.17 3.48 3.86 4.24 4.65 5.08 5.53 6.02 6.54 7.10 i.m 8.32 8.99 9.70 10.45 10 2.814. 1.75 2.03 2.30 2.57 2.85 3.15 3.46 3.84 4.22 4.62 5.as 5.51 6.00 6.52 7.08 7.67 8.30 8.97 9.68 10.43 12 3.338 1.73 2.01 2.27 2.54 2.83 3.12 3.43 3.81 4.19 4.59 S.02 5.48 5.96 6.48 7.04 7.63 8.26 8.93 9.64 10.39 3.665 1.72 2.0C 2.26 2.53 2.81 3 11 3.41 3.79 `4.17 4.57 5.00 5.40 5.94 6.47 7.02 7.61 8.24 8 91 9.62 10.37 16 4.189 1.70 1.98 2.24 2.51 2.79 3.08 3.39 3.77 4.14 4.55 4.98 5.43 5.92 6.44 6.99 7.59 8.21 8.88 9.59 10.34 18 20 24 face 4.717 5.5536 6.283 1.69 1.6S 1.6C 1.84 1.96 1.95 1.92 2.14 2.22 2.2) 2.1( 2.42 2.49 2.47 2.45 2.7C 2.77 2.75 2.72 3.0C 3.07 3.05 3 0? 3.3C 3 37 3.3 3.33 3.62 3.75 4.12 4.53 3.73 4.11 4.51 3.70 4.07 4.45 4.00 4.35 4.71 4.96 4.94 4.91 5.22 5,41 6.39 5.30 5.68 5.90 5.88 5.84 6.17 6.42 6.41 6.36 6.7C 6.97 7.56 6.95 7.54 6.92 7.51 7.20 7.85 8.19 8.86 9.57 10.32 8.17 8.84 9.55 10.29 8.14 8.81 9.51 10.26 8.4* 9.15 9.80 10.62 Horisontal Surface Facing Upward - 2.03 2.37 2.67 2.97 3.28 3.59 3.92 4.31 4.70 5.12 5.56 6.02 6.52 7.05 7.61 8.21 8.86 9.52 10.24 10.99 Horizontal Surface Facing Downward 1.61 1.86 2.11 2.36 2.64 2.93 3.23 3.60 3.97 4.37 4.80 5.25 5.73 6.25 6.80 7.39 8.02 8.69 9.39 10.14 Value* ere for Viet Surface* four eooare feet or more in ute To eeeur* !" per --r foot, multiply sq ft loose* in by this factor. The toeeee per eq ft of pipe surface for pipes terser than ?4 in. can be eossidered the same as the lease* for the pipe. . between the pipe and the surrounding atmosphere up to 525 F, are shown in Figs. 1,2, and 3. The actual thicknes of many molded pipe coverings is not exactly 1 in. However, the loss through any given thick ness of insulation can be obtained by interpolation. The heat losses through 1, lVz, and 2-in. thick block, blanket, or cement insulation when applied to a flat vertical surface is given in Fig. 4. The lceses through any of the insulations given in Table 1 <*ftn be obtained by multiplying the losses obtained from Figs. 1,2,3, or 4 by the factors given in Table 6. Pipes operating at high temperatures are frequently in sulated to the best advantage by combining a high tempera ture ingi^ntinn near the pipe with a' moderate or low tem perature 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 two or three calculations performed as a series of approximations, in which assumptions of thick ness and mean temperature are adjusted as indicated in the discussion which follows. In the'case of a angle thickness of pipe covering, the quan tity of heat transferred per square foot of outer surface of the insulation is given by the equation: ,.. a <i) r, log. --r* Ti where 9. TM Btu per (hour) (square foot of outer surface of insula tion). rt " outer radius of pipe or inner radius of insulation, inches.. r* -- outer radius of insulation, inches. k = thermal conductivity of insulation,, Btu per (hour) (square foot) (Fahrenheit degree per inch). It " temperature of inner surface of insulation, Fahrenheit. tt ** temperature of outer surface of insulation, Fahrenheit. Pipe and Industrial Insulation 457 Table 3 .... Heat Loss from Horizontal Tarnished Copper Fipe1 Expressed in BJu par (boar) (Cneor foot) (fuhranbetf degree difference between the pipe and arroaoding pill air at 70 f) Hoi Water (Type K Clipper Tube) Stoum (Standard Pipe Size Fipe) Nomine! Pipe 120F Size 150 F 180 F 210 F 227.1 F (5 psig) 2977 f |50p*Jg) 337.9 F (100 pwgl Temperature Difference--F Oeg Table 4 .... External Surface per Linear Foot of Copper Tubing Oufsd* cfiomdi* X in. greater than nominal dza Tube Size Surface Area Surface Area Tube Size Surface Area (Jadwil (Sq Pi) (Inches) (Sq Ff) (Indie*) (Sq Ft) K 0.164 2 0.556 5 1.342 X 0.229 2X 0.687 6 1.604 1 0.295 3 0.818 8 2.128 IK 0.360 m 0.949 IX 0.426 4 1.080 50 80 110 140 157.1 2277 267.9 X 0.250 0.287 0.300 0.321 0.433 0.500 0.530 H 0.340 0.381 0.409 0.429 0.533 0.543 0.654 l 0.440 0.475 0.509 0.536 0.636 0.746 0.803 1H 0.500 0.559 0.618 0.622 0.764 0.878 0.934 IX 0.580 0.656 0.710 0.750 0.904 1.053 1.120 2 0.730 0.825 0.890 0.957 1.101 1.273 1.364 2* 0.880 1.000 1.091 1.143 1.305 1.490 1.605 3 1.040 1.175 1.272 1.343 1.560 1.800 1.940 3K 1.180 1.350 1.454 1.535 1.750 2.020 2.170 4 1.460 1.500 1.635 1.715 1.941 2.240 2.430 *X 5 2.131 2.465 2.650 i.600 i.8i2 i .980 2.071 2.387 2.770 2.990 6 1.840 2.125 2.270 2.430 2.740 3.210 3.440 8 2.400 2.685 2.910 3.110 3.310 4.050 4.370 The heat Io6s through two or more thicknesses of insulation applied to a pipe can be calculated by means of the equation: r. liog. --r* r, lo, g, --u r ,r where r< D outer radius of second layer of insulation, inches. r, = outer radius of last layer of insulation. Inches. The method of solving Equation 2, which is the most diffi cult of the two, is given in Example 3. It is convenient to work from the outer surface of the in sulation, since the loss through the covering must be determined'from the outer surface loss by means of surface Joss curves such as given in Fig. 5. The curves were plotted from tests conducted at the Mellon Institute. After the true heat loss is obtained, the loss per square foot of pipe surface can be calculated from the relationship: ?. - 9(rtAi) where 9> = Btu per (hour) (square foot outer surface of pipe). Example 3: Compute the heat loss per linear foot of pipe sur face per hour from a 6-in. pipe, insulated with a 3-in. tiiinlmwi of 1500 F diatomaceous earth, and a nominal 2-in. thickness of 85 percent magnesia. The pipe is operating at a temperature of 1200 F and is exposed to a room temperature of 80 F. Solution:. In figuring the heat loss from Equation 2, it is necessary to first make an assumption for the outer surface tem perature t> and the temperature between the diatomaceous earth and 85 percent magnesia insulation, so that the mean tempera ture of each material can be obtained and the thermal conduc tivity corresponding to the mean temperature of each material substituted in the equation. First assume an outer surface tem perature of 135 F and a temperature of 570 F between the two materials corresponding to a mean temperature of (1200 + 570) 2 or 885 F for the diatomaceous earth and (570 + 135) 2 or 352.5 F for tile 85 percent magnogjn insulation. The conduc- Table 5 .... Area of Hanged fittings, Square Feet* Nominai Pipe Size (inches) Flanged Coupling Standard Extra 90 Deg Bi long Rodfo SI Tee Crass Standard Extra Heavy Standard Extra Heavy Standard Extra Heavy Standard Extra Heavy 1 0.320 0.438 0.795 1.015 0.892 1.083 1.235 1.575 1.622 2.07 IK 0.383 0.510 0.957 1.098 1.084 1.340 1.481 1.925 1.943 2.53 IX 0.477 0.727 1.174 1.332 1.337 1.874 1.815 2.68 2.38 3.54 0.672 0.848 1.65 2.01 1.84 2.16 2.54 3.09 3.32 4.06 2X 0.841 1.107 2.09 2.57 2.32 2.76 3.21 4.05 4.19 5.17 3 0.945 1.484 2.38 3.49 2.68 3.74 3.66 5.33 4.77 6.95 3K 1.122 1.644 2.9$ 3.96 3.28 4.28 4.4S 6.04 5.83 7.89 4 1.344 1,914 3.53 4.64 3.96 4.99 5.41 7.07 7.03 9.24 4K 1.474 2.04 3.95 5.02 4.43 5.46 6.07 7.72 7.87 10.07 5 1.622 2.18 4.44 5.47 5.00 6.02 6.81 8.52 8.82 10.97 6 1.82 2.78 5.13 6.99 5.99 7.76 7.84 10.64 10.08 13.75 8 2.41 3.77 6.98 9.76 8.56 11.09 10.55 14.74 13.44 18.97 3.43 5.20 10.18 13.58 12.35 15.60 15.41 20.41 19.58 26.26 4.41 6.71 13.08 17.73 16.35 18.76 19.67 26.65 24.87, 34.11 * Including were at accompanying flung** bolted to the fitting.