Identifier: heatengineeringt00gree (find matches)
Title: Heat engineering; a text book of applied thermodynamics for engineers and students in technical schools
Year: 1915 (1910s)
Authors: Greene, Arthur Maurice, 1872- (from old catalog)
Subjects: Thermodynamics
Publisher: New York (etc.) McGraw-Hill book company, inc.
Contributing Library: The Library of Congress
Digitizing Sponsor: The Library of Congress

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or an engine may be drawn and studied. SPEED The speed of an engine affects its efficiency in changing theamount of condensation. As this varies inversely as the cuberoot of the number of revolutions per minute it would naturallybe expected that high-speed engines would be the more efficient.That this is not so is due to the fact that the term s variesinversely as the linear dimension of the engine and hence thisterm is so small for large engines that it overbalances the effectof the slower speed. For instance, if the piston speed, 2LN, isfixed, the initial condensation will vary approximately inverselyas the cube root of N and also inversely as the square root ofL. Hence it would pay to make L large and N small. This isthe actual result in practice. The large, slow-speed pumping 234 HEAT ENGINEERING engines represent the best type of engines using saturatedsteam. The effect of superheat has been explained and results givenat the end of Chapter II show that this materially affects the
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condensation and increases the efficiency a greater amount thanthat estimated by theory. The effect of the jacket on a cylinder is a debated question.The results shown by the committee of the Institution of Me- THE STEAM ENGINE 235 chanical Engineers of Great Britain indicate a distinct gain.Other tests made on large engines show no gain and, in a fewcases, a loss. Of course the total steam used by the engine isalways considered in these cases. In most instances the importantsaving has been found on small engines of less than 300 h.p.For large engines the results will vary. Ten to 15 per cent,may be saved on engines of 200 or 300 h.p. One form of jacketwhich has been used on the type of semiportable engine knownas the locomobile is of value. In this unit the engine is mountedon top of the boiler, Fig. 109, and the exhaust gases from theboiler pass around the cylinder, thus heating it to a high tempera-ture. These units have the condensation reduced to such a de-gree by this jacket com

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