Heat engineering; a text book of applied thermodynamics for engineers and students in technical schools . valueof r this condensation effect is smaller but there is a loss fromfree expansion. If the results of a test are plotted with indicated horse-poweras abscissae and total weight of steam per hour as ordinates, themost efficient point is found at the point of tangency of a straightline from the origin as this gives the smallest ratio of ordinate THE STEAM ENGINE 223 to abscissa which is the steam per horse-power hour. In this relation is seen for the curve AB. If the ratios ofordin
Heat engineering; a text book of applied thermodynamics for engineers and students in technical schools . valueof r this condensation effect is smaller but there is a loss fromfree expansion. If the results of a test are plotted with indicated horse-poweras abscissae and total weight of steam per hour as ordinates, themost efficient point is found at the point of tangency of a straightline from the origin as this gives the smallest ratio of ordinate THE STEAM ENGINE 223 to abscissa which is the steam per horse-power hour. In this relation is seen for the curve AB. If the ratios ofordinates to abscissae are found for different points, the steamconsumption curve CD is found on which F is the best point. Heck proposes that the weight of steam per hour be dividedby the displacement per hour giving the weight of steam used percubic foot of displacement. In this case the line AB would takethe same form because the displacement per hour which is 120FLN . , ? . _. inn -, is a constant for Fig. 100. 144 F = area of piston in square inches. L = stroke in feet. .V = revolutions per Mean Effective Pressure Fig. 101.—Curves of steam per cu. ft. of displacement for different mean effective pressures. This quantity is called m,/, weight per cubic foot of displacement,wt. per hr. Now m/_ 120FLN144 = const. X wt. per hr. from which p, = 33000 2pmFLN33000 = const. X (70) In Fig. 101 the line AB drawn with pm and mf as coordinatesis the same curve as used before with a new scale. The weight 224 HEAT ENGINEERING of steam per cubic foot of piston displacement from the indi-cator card, Fig. 102, when the missing quantity is , is (I + x)D 1 - 1 - D (>+t)« .+ vb Ve 1 — m/ = 1 (rv\)() approximately. (71)
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