File:Applied thermodynamics for engineers (1913) (14579724690).jpg

Identifier: appliedthermodyn01enni (find matches)
Title: Applied thermodynamics for engineers
Year: 1913 (1910s)
Authors: Ennis, William Duane, 1877-
Subjects: Thermodynamics
Publisher: New York, Van Nostrand
Contributing Library: The Library of Congress
Digitizing Sponsor: The Library of Congress

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efficiency. The reason for these high values, exceedingunity, has been stated in Art. 621. The steam engine efficiencies in noneof these tests exceeded 15 per cent; it did not average much over 5 percent; an average efficiency of 0.237 from coal to room corresponds to acoefficient of performance of about 0.237-7-0.05=4.74 (neglecting friction of mechanism). The engine to room efficiency is equal to the actual coefficient of perform-ance multij)lied by the mechanical efficiency of engine and compressor. 663. Ammonia Absorption Machines. Assuming an evaporation of 11.1 lb. ofwater from and at 212^ F. per pound of combustible, Ledoux (24) reports a testin which 20.1 lb. of ice-melting effect were produced per pound of coal, the over-all efficiency being tluis 0.204. A seven-day test by Denton (25) gave 17.1 lb.,based on 10 lb. of steam per pound of coal, the corresponding efficiency beingabout 0.173. The pressure range was from 23.4 to 150.77 lb. absolute. The tem- AMMONIA COMPRESSOR 483
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484 APPLIED THERMODYNAMICS perature range was from 272° to 80° F.; the coefficient of performance for theCarnot cycle would have been 2.83. The equivalent efficiency from coal to com-pressor cylinder in a compression machine must then have been at least 0.173 - 2.83 = 0.0613;or from coal to engine cylinder, about 1.2 X 0.0612 =. 0.07344. 664. Commercial Types. Compressors may be driven directly from a steamcylinder, or by belt. Any form of slov/-speed engine may be used for driving;a favorite arrangement is to have the steam cylinder horizontal and the ammoniacylinder vertical, as in Fig. 313. Tandem or cross-compound engines may beused. The ammonia condenser may be an ordinary surface condenser, or anatmospheric condenser of the form described in Art. 585, consisting of a coil ofexposed pipes over which streams of water trickle. In other types, the ammoniacoils are submerged in a tank of circulating water. Cooling towers are usedwhere there is an inadequate water supply. (1) WsiWis

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