The following table gives the draught area and heating surface of the various sized boiler tubes and flues: External
Diameter. | Draught area
in sq. inches. | Draught Area
in sq. feet. | Heating surface
in feet per ft. of
tube in length. | No. of tubes
in 1 sq. foot of
draught area. | | 5/8 | ...... | ...... | .1636 | ..... | | ¾ | ...... | ...... | .1963 | ..... | | 1 | .575 | .0040 | .2618 | 250.0 | | 1¼ | .968 | .0067 | .3272 | 149.3 | | 1½ | 1.389 | .00964 | .3927 | 103.7 | | 1¾ | 1.911 | .0133 | .4581 | 75.2 | | 2 | 2.573 | .0179 | .5236 | 55.9 | | 2¼ | 3.333 | .0231 | .5891 | 43.3 | | 2½ | 4.083 | .0284 | .6545 | 35.2 | | 2¾ | 5.027 | .0349 | .7200 | 28.7 | | 3 | 6.070 | .0422 | .7854 | 23.7 | | 3¼ | 7.116 | .0494 | .8508 | 20.2 | | 3½ | 8.347 | .0580 | .9163 | 17.2 | | 3¾ | 9.676 | .0672 | .9818 | 14.9 | | 4 | 10.93 | .0759 | 1.0472 | 13.2 | | 4½ | 14.05 | .0996 | 1.1781 | 10.2 | | 5 | 17.35 | .1205 | 1.3090 | 8.3 | | 6 | 25.25 | .1753 | 1.5708 | 5.7 | | 7 | 34.94 | .2426 | 1.8326 | 4.1 | | 8 | 46.20 | .3208 | 2.0944 | 3.1 | | 9 | 58.63 | .4072 | 2.3562 | 2.5 | | 10 | 72.23 | .5016 | 2.6180 | 2.0 |
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