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American Society of Heating and Ventilating Engineers Guide, 1934 Table 4. Conductivities (k) of Various Types of Insulating Materials for Medium and High Temperature Pipes Mean Temperature (4 Plies per 1 in. thick) (8 Plies per 1 in. thick) (30-40 Laminations per 1 in. thick) (20 Laminations per 1 in. thick) (Diatomaceous Earth and Asbestos) (Felted Fibre) 100 F 0.425 0.530 200 F 0.465 0.650 300 F 0.505 0.770 400 F 0.550 0.890 500 F 0.590 0.480 0.555 0.630 0.705 0.360 0.415 0.470 0.525 0.585 0.545 0.605 0,665. 0.725 0.785 0.350 0.410 0.470 0.530 0.590 0.515 0.545 0.575 0.605 0.635 0.600 0.640 0.675 0.715 0.750 ^Mechanical Engineer's Handbook, Marks, 3rd Ed., 1930. conductivities makes it possible readily to calculate the heat loss through single or compound sections. It should be emphasized that the con ductivities given in Table 4 for the various insulations are the average of values obtained from a number of tests made on each type of material, also that all variables due to differences in thickness, pipe sizes, and air conditions are eliminated. Individual manufacturer s materials will, of course, vary in conductivity to some extent from these values. The heat losses through six of the types of insulation given in Table 4 for 1, llA and 2-in.-thick materials, and for temperatures commonly encountered in engineering practice can be obtained from Tables 5 to 10, inclusive. The loss through other thicknesses of the materials, and for other hot water or steam temperature conditions may be obtained by interpolation. The heat loss coefficients given in Tables 5 to 10 are based on the conductivities in Table 4 and were computed from data given in Chapter 22, The Guide 1931, as in the following problem: Example 1. Determine the totalheat loss for a period of 30 days through a 1-in. (4 ply) thickness of corrugated asbestos insulation on 100 ft of 3-in. pipe carrying steam at 5 lb pressure, and with, surrounding air at 60 F. Also determine percentage of heat saving over bare pipe loss. Solution. Difference in temperature between pipe and surrounding air - 227.1 -- 60 or 167 1 deg. From Table 6 the coefficients of transmission for 1-in. corrugated asbestos (4 ply) are 0.608 and 0.652 Btu per hour per square foot per degree temperature difference at temperature differences of 157.1 deg and 227.7 deg, respectively. The difference is 0.044 Btu per hour per square foot per degree temperature difference lor a temperature difference of 70.5 deg.' For a temperature difference of 167^1 deg (10 deg higher than 157.1 deg) the coefficient of transmission is then 0.608 + (jqI; X 0.044J, or 0.614 Btu per hour per square foot per degree temperature difference. From Table 2 the area per linear foot of 3-in. pipe is 0.917 sq ft. The total h.t loss is therefore 0.917 X 0.614 X 167.1 X 100 (linear feet) X 720 (hours) = 6,774,000 Btu. From Table 1, and in the same manner it is determined that the loss through an uninsulated 3-in. pipe for the same conditions will be 25,917,000 Btu. The saving due to insulation is 19,143,000 Btu or 74 per cent of the bare pipe loss. 506 Chapter 35--Heat Losses from Bare and Insulated Pipes Table 5. Coefficients of Transmission (U) for Pipes Insulated with 85 Per Cent Magnesia Type Insulation These coefficients are expressed in Btu per hour per square foot of pipe surface per degree Fahrenheit difference in temperature between pipe and surrounding still air at70F Thickness of Insulation (Inches) i m Nominal Pipe Size (Inches) X liixxX 2 2X 3 3X 4 4X 5 6 8 9 12 A X l IX IX 2 2A 3 3X 4 4X 5 6 8 9 12 120 F S0F 0.744 0.672 0.613 0.562 0.532 0.500 0.475. 0.455 0.441 0.429 0.420 0.411 0.402 0.387 0.380 0.369 Hot Water I 150 F 180 F 1210 F 227.1 F (5 Lb) Temperature Difference Steam 297.7 F (50 Lb) 80 F 110 F 140 F I 157.1 F 227.7 F 0.754 0.681 0.621 0.570 0.539 0.506 0.481 0.461 0.447 0.435 0.425 0.416 0.408 0.392 0.385 0.374 0.764 0.689 0.629 0.577 0.546 0.512 0.487 0.467 0.452 0.441 0.431 0.422 0.413 0.397 0.390 0.378 0.774 0.779 0.697 0.701 0.637 0.641 0.585 0.589 0.553 0.557 0.519 0.523 0.493 0.497 0.474 0.477 0.458 0.462 0.446 0.449 0.437 0.440 0.427 0.430 0.419 0.422 0.403 0.405 0.395 1 0.398 0.383 0.386 0.802 0.721 0.659 0.606 0.573 0.538 0.512 0.492 0.475 0.463 0.453 0.443 0.435 0.418 0.410 0.398 337.9 F (100 Lb) 267.9 F 0.814 0.731 0.670 0.617 0.582 0.547 0.520 0.500 0.483 0.471 0.460 0.450 0.442 0.425 0.417 0.405 0.617 0.550 0.496 0.453 0.424 0.394 0.371 0.352 0.339 0.328 0.320 0.312 0.303 0.287 0.280 0.272 0.625 0.558 0.503 0.459 0.430 0.400 0.376 0.357 0.343 0.333 0.324 0.316 0.307 0.291 0.284 0.275 0.633 0.566 0.511 0.465 0.436 0.405 0.382 0.362 0.347 0.337 0.328 0.320 0.311 0.295 0.288 0.279 0.642 0.573 0.518 0.472 0.442 0.410 0.386 0.367 0.351 0.341 0.332 0.324 0.315 0.299 0.292 0.283 0.646 0.577 0.522 0.475 0.445 0.413 0.389 0.370 0.354 0.343 0.334 0.326 0.318 0.301 0.294 0.285 0.665 0.596 0.540 0.490 0.459 0.427 0.401 0.380 0.364 0.353 0.343 0.336 0.328 0.311 0.303 0.294 0.676 0.606 0.549 0.498 0.467 0.434 0.408 0.387 0.370 0.359 0.350 0.342 0.333 0.316 0.308 0.299 X 0.543 0.551 0.558 0.565 0.569 0.587 0.597 X 0.484 0.490 0.497 0.503 0.507 0.523 0.532 ix1 0.433 0.439 0.445 0.451 0.454 .0.467 0.476 0.393 0.398 0.403 0.409 0.412 0.424 0.432 IX 0.365, 0.370 0.376 0.381 0.384 0.397 0.402 2 0.338 0.343 0.347 0.351 0.354 0.364 0.370 2X 0.316 0.320 0.324 0.328 0.331 0.341 0.347 3 0.297 0.301 0.305 0.309 0.312 0.321 0.326 2 3X 0.284 0.288 0.292 0.295 0.297 0.306 0.311 4 0.275 0.278 0.282 0.285 0.287 0.296 0.301.. 4X 0.266 0.270 0.273 0.276 0.278 0.286 0.290 5 0.258 0.262 0.265 0.268 0.270 0.278 0.283 6 0.250 0.254 0.257 0.260 0.262 0.270 .0.274 8 0.236 0.239 0.242 0.245- 0.247 0.255 0.258 9 0.228 0.231 0.234 '0.237 0.239 0.246 0.250 12 0.219 0.222 0.225 0.228 0.230 0.237 0.240