Book - School of Science and Technology

External distribution systems 171Data for steam pipeworkTable 6.14 Theoretical heat emission from horizontal pipes (bare steel to BS 1387)Nominalbore(mm)Heat emission (W/m run) to ambient air at 20 C for followingabsolute steam pressures (kPa)100 200 300 400 500 600 700 800 900Nominalbore(mm)10 61 82 94 105 118 131 138 145 151 1015 100 135 154 173 194 215 227 238 250 1520 122 164 188 211 237 262 276 290 304 2025 149 200 227 257 289 320 338 355 372 2532 181 244 279 314 353 391 413 434 455 3240 203 273 313 352 395 438 462 486 510 4050 246 331 379 427 480 532 561 590 619 5065 301 406 465 523 588 653 689 725 761 6580 345 466 533 600 675 750 792 833 874 80100 431 582 666 750 844 937 988 1039 1090 100125 515 695 796 897 1009 1120 1183 1245 1308 125150 589 808 924 1040 1175 1310 1385 1460 1515 150Table 6.15 Theoretical heat emission from horizontal pipes (with insulation of stated thickness) aNominalbore(mm)Heat emission (W/m run) to ambient air at 20 C for followingabsolute steam pressures (kPa)100 200 300 400 500 600 700 800 900Insulationthickness(mm)10 15 18 20 21 22 22 23 23 24 5015 15 19 21 23 25 27 28 29 30 5020 17 21 23 25 27 29 30 32 33 5025 19 24 26 29 31 34 35 36 37 5032 22 27 30 32 35 38 39 41 42 5040 23 29 32 35 38 41 42 44 45 5050 26 33 36 40 43 46 48 50 51 5065 28 35 39 42 46 49 51 53 54 6580 31 39 43 47 51 55 57 59 60 65100 36 45 50 54 59 63 65 68 70 65125 41 51 56 61 66 71 74 77 79 65150 46 57 63 68 74 80 83 86 88 65a Insulation conductivity ˆ 0:055 W/m K.As to the materials available, wet applications are a thing of the past and the remainingoptions relate largely to the quality of the finish.External distribution systemsIt is not unusual that, in the design of a heating system for a large site, the matter ofexternal pipe distribution arrangements has to be considered. There are three possiblesolutions to this problem: