Document 10VERNO2R7q5k065qzk3NjeOq

1936American Society of Heating and Ventilating Engineers Guide, Table 11. Coefficients of Transmission (U) for Pipes Insulated, with Rock Wool 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 at 70 F Thickness or Insolation (Inches) i iA 2- Nominal Pipe Sob (Inches) A K l m ia 2. VA 3 3'A 4 4A 5 6 8 10 12 A lM ml A 2 2A 3 3A 4 4A 5 6 8 10 12 A % l m lA 2 TA 3 3A 4 4A 5 6 8 10 12 120 F 50 F 0.631. 0.569 0.518 0.476 0.450 0.422 0.402 0.385 0.373 0.363 0.355 0.348 0.341 0.327 0.317 0.313 Hot Water 150 F 180 F 210 F 227.1 F. (S Lb) Temperature Difference 80 F UOF 140 F 157.1 F 0.644 0.581 0.529 0.486 0.460 0.431 0.411 0.394 0.381 0.371 0.363 0.356 0.348 0.335 0.324 0.320 0.658 0.593 0.541 0.497 0.470 0.441 0.420 0.402 0.389 0.379 0.371 0.364 0.356 0.342 0.331 0.327 0.672 0.606 0.552 0.507 0.480 0.450 0.428 0.411 0.398 0.387 0.379 0.371 0.363 0.349 0.338 0.334 0.680, 0.613 0.559 0.513 0.485 0.456 0.434 0.415 0.402 0.392 0.383 0.376 0.368 0.353 0.343 0.338 Steam 297.7 F (50 Lb) 227.7 F 0.712 0.642 0.585 0.537 0.508 0.478 0.455 0.435' 0.421 0.4110.402 0.394 0.386 0.372 0.360 0.355 337.9 F <100 Lb) - 267.9 F 0.730 0.659 0.600 0.551 0.522 0.490 0.466 0.446 0.432 0.422 0.413 0.404 0.396 0.381 0.369 0.364 0.523 0.468 0.421 0.383 0.359 0.333 0.314 0.296 0.286 0.278' 0.270 0.263 0.257 0.244 0.235 0.230 0.534 0.477 0.430 0.391 0.366 0.340 0.320 0.302 0.291 0.284 0.276 0.269 0.262 0.249 0.240 0.234 0.545 0.487 0.440 0.399 0.375 0.348 0.327 0.310 0.298 0.290 0.282 0.275 0.267 0.254 0.245 0.239 0.556 0.497 0.449 0.407 0.383 0.356 0.335 0.317 0.304 0.296 0.287 0.280 0.273 0:260 0.250 0.245 0.563 0.503 0.455 0.412 0.387 0.360 0.339 0.321 0.307 0.300 0.291 0.284 0.277 0.263 0.253 0.247 0.590 0.528 0.477 0.433 0.407 0.378 0.355 0.337 0.323 0.315 0.305 0.298 0.290 0.276 0.265 0.260 0.606 0.542 0.490 0.444 0.419 0.389 0.365 0.347 0.332 0.323 0.313 0.305 0.297 0.283 0.272 0.267 0.461 0.409 0.366 0.333 0.310. 0.286 0.268 0.252 0.241 0.232 0.225 0.218 0.213 0.200 0.189 0.185 0.471 0.418 0.374 0.340 0.316 0.292 .0.274 0.257 0.246 0.237 0.230 0.223 0.217 0.204 0.193 0.190 0.481 0.427 0.382 0.347 0.323 0.298 0.279 0.262 0.251 0.242 0.235 0.228 0.221 0.208 0.197 0.194 0.491 0.436 0.390 0.355 0.330 0.304 0.285 0.268 0.257 0.247 0.240 0.233 0.226 0.213 0.201 0.198 0.496 0.441 0.395 0.359 0.334 0.308 0.289 0.272 0.260 0.250 0.243 0.236 0.228 0.215 0.204 0.200 0.520 0.463 0.415 0.377 0.351 0.323 0.302 0.284 0.272 0.262 0.255 0.247 0.239 0.225 0.214 0.210 0.534 0.475 0.427 0.387 0.360 0.331 0.310 0.292 0.280 0.269 0.262 0.253 0.245 0.231 0.220 0.216 36Chapter --Insulation of Piping inclusive. The loss through other thicknesses of the materials, and for hot water or steam temperature conditions may be obtained by fntemolation. The heat loss coefficients given in Tables 6 to lljare on the conductivities in Table 5 and were computed from data given in Chapter 22, The Guide 1931. LOW TEMPERATURE PIPE INSULATION `Surfaces maintained at low temperatures should be insulated so as to retard the flow of heat from the outside into the low temperature area and to orevent the formation of condensation and of frost if the temperatures are low enough, as well as to prevent corrosion induced by the presence of condensed moisture on metal surfaces. Materials commonly used for insulating pipes and surfaces at low temperatures are cork, rock cork hair felt and other felted or fibrous non-absorbent materials. Thermal conductivities of low temperature insulating materials are given m Chapter 5. . Insulating materials are available commercially to meet varying tem- oerature gradients. For example, the thickness of insulation for ice water is approximately V/i in. if the temperature in the line is not lower than 25 F- the thickness of insulation for brine is approximately 2^ in. where the temperature ranges from 0 deg to 25 F; and the thickness of insulation where the brine temperature ranges from --30 F to zero degrees is ap proximately 4 in. Insulation to Prevent Freezing If the surrounding air temperature remains sufficiently low for an ample period of time, insulation cannot prevent the freezing of still water, or of water flowing at such a velocity that the quantity of heat carried in the water is not sufficient to take care of the heat losses which will result and cause the temperature of the water to be lowered to the freezing point Insulation can materially prolong the time required for the water to give up its heat, and if the velocity of the water flowing in the pipe is maintained at a sufficiently high rate, freezing may be prevented. Table 12 may be used for making estimates of the thickness of insulation necessary to take care of still water in pipes at various water and surrounding air temperature conditions. Because of the damage and service interruptions which may result from frozen water in pipes, it is essential that the most efficient insulation be utilized. This table is based on the use of hair felt or cork, having a conductivity of 0.30. The initial water temperature is assumed to be 10 deg above, and the sur rounding air temperature 50 deg below the freezing point of water (tem perature difference, 60 F). The last column of Table 12 gives the minimum quantity of water at initial temperature of 42 F which should be supplied every hour for each linear foot of pipe, in order to prevent the temperature of the water from being lowered to the freezing point. The weights given in this column should be multiplied by the total length of the exposed pipe line expressed in feet. As an additional factor of safety, and in order to provide against temporary reductions in' flow occasioned by reduced pressure, it is advisable to double the rates of flow listed in the table. It must be 663