The Elements of Civil Engineering; Prepared for Students of the International Correspondence Schools, Scranton, Pa... . Volume 6

This historic book may have numerous typos and missing text. Purchasers can usually download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1899 edition. Excerpt: ...of pounds of water which a pound of coal will raise from 60 and evaporate into steam at 80 lb. pressure. As will be explained later, it is customary, for the purpose of calculation, to reduce both Wand 2 to the equivalent evaporation from and at 212 F. ExAMPLE.--Find the grate area of an 80 H. P. boiler, evaporating 30 lb. of water from and at 212 per H. P. per hour, the rate of combustion being 12 lb. per sq. ft. of grate surface per hr., and the evaporation 1011-lb. of water from and at 212 per pound of coal. 1831. The heating surface of a boiler includes the entire surface of the shell and flues coming in contact with the flame and furnace gases on one side and water on the other; this includes, in the case of externally fired boilers, the portion of the shell below the fire line, portions of the heads, and the inner surface of fire tubes and flues, or the outer surface of water tubes. In the case of internally fired boilers, the heating surface includes the interior of the firebox, or furnace flues, and the inner surface of the tubes, if there are any. The area of the heating surface of each of the various types of boilers bears a nearly constant ratio to the grate area. The ratios usually adopted are as follows: Plain cylindrical boilers........................ 12 to 15 Cornish....................................... 15 to 30 Cylindrical flue................................ 20 to 25 Cylindrical tubular............................ 25 to 35 Marine fire tubular............................ 30 to 35 Marine water tubular.......................... 35 to 40 Locomotive tubular............................ 50 to 100 1832. From a large number of tests of horizontal tubular boilers, Mr. G. H. Barrus concludes that the ratio of heating surface to...