Heat engineering; a text book of applied thermodynamics for engineers and students in technical schools . . The ratio of 775 to 773 is called the practical efficiency, 774, andshows how near the actual efficiency approaches the efficiencydemanded by theory and a low value of this means that therehave been errors in actually applying the cycle. To make thisterm larger, jackets, superheated steam, and reheaters have beenapplied to steam engines. * - ir ^ If the mechanical efficiency 776 is the ratio of the output tothat developed within the machine or shown by the indicatorcard, this effi
Heat engineering; a text book of applied thermodynamics for engineers and students in technical schools . . The ratio of 775 to 773 is called the practical efficiency, 774, andshows how near the actual efficiency approaches the efficiencydemanded by theory and a low value of this means that therehave been errors in actually applying the cycle. To make thisterm larger, jackets, superheated steam, and reheaters have beenapplied to steam engines. * - ir ^ If the mechanical efficiency 776 is the ratio of the output tothat developed within the machine or shown by the indicatorcard, this efficiency is found by 64 HEAT ENGINEERING VG = output indicated work AWoAWa (7) The overall efficiency is then the product of certain of thesevarious efficiencies. output V = (8) heat supplied The overall efficiency being the product of these, the efficiencymay be increased by increasing any of them. In cases such as thegas engine 771 is so great that although 772 and 776 are small theproduct is greater than that of the steam engine. These variousefficiencies will be investigated for different Fig. 20.—pV and TS diagrams of cycles. The quantity A Wa may be found from the area of the cycle onthe pv plane or from the area on the T-S plane in Fig. 20, if thelines are reversible lines. Of course on the pv plane 123456represents positive work while 6571 represents negative workand hence 723457 represents the network. On the T-S plane, 123456 represents Qi if there is no friction,and 6571 represents Q2 under these conditions, hence the areaof the cycle represents Qi ~- Q2 or the work done. If, however,there is friction 12345 = Qi + H1and 6571 = (- Q2 + H2) since the heat removed to the outside from 5 to 7 is morethan that shown by the area on account of the heat developed byfriction. 23457 = Q1 - Q2 + (#1 + #2) = AW + #1 + H2 HEAT ENGINES AND EFFICIENCIES 65 or the area is greater than the work of the cycle. In any casean irreversible line makes the work less than the area
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Keywords: ., bookcentury1900, bookdecade1910, bookpublishernewyo, bookyear1915
