Heat engineering; a text book of applied thermodynamics for engineers and students in technical schools by Greene Arthur Maurice 1872-

Author:Greene, Arthur Maurice, 1872- [from old catalog]
Language: eng
Format: epub, pdf
Tags: Thermodynamics
Publisher: New York [etc.] McGraw-Hill book company, inc.
Published: 1915-03-25T05:00:00+00:00

PROBLEMS

Problem 1. —Find the various efficiencies of an engine with p x = 120 lbs. gauge pressure, p 2 = 30 lbs. gauge pressure, p 1 = 2 lbs. gauge pressure if xi = 0.99 and 35 lbs. of steam are needed per i.h.p.-hr.

Problem 2.—One engine uses 25 lbs. of steam per i.h.p.-hr. with steam at 125 lbs. gauge pressure and of quality 0.995. The back pressure is 2 lbs. by gauge. By using steam of 200° F. superheat the steam consumption is reduced to 22 lbs. per i.h.p.-hr. What was the saving?

Problem 3.—An engine uses 3500 lbs. of steam per hour, of which 300 lbs. is used in the jackets and 200 lbs. in the receiver. The steam supply is at 150 lbs. gauge pressure with 175° F. superheat. The temperature of the return from the jackets is 320° F., while the return from the receiver is 338° F. and the hot well temperature from the condensate is 95° F. The engine develops 250 h.p. Find the B.t.u. per h.p.-min. Find the actual efficiency. If the mechanical efficiency of the pump and engine combined is 92 per cent., what is the duty of this engine?

Problem 4. —In Fig. 68 assume that the pressure on the top line is 120 lbs. absolute and on the lower line is 15 lbs. absolute. Suppose that the quality on the top line is 0.98, assuming the cycle to be the Rankine cycle, and that it varies from 0.03 to 0.98 if assumed to be the Carnot cycle. Find the qualities at the lower corners. Find the heats on the four lines.

Problem 5. —In a Rankine cycle with complete expansion the pressure varies from 125 lbs. gauge to 0 lbs. gauge with x\ = 1.0. Find the efficiencies, 771, 772,773- Increase the upper pressure to 150 lbs. gauge and, leaving the other quantities unchanged, find 771, 772 and 773. With 125 lbs. initial gauge pressure assume the quality changes to 160° F. superheat; find 771, 772 and 773. Assume the back pressure is changed to a vacuum of 27 in. but with no change in other conditions; find 771, 772 and 773.

Problem 6. —In a Rankine cycle with incomplete expansion let the initial gauge pressure be 125 lbs., the pressure at the end of expansion 20 lbs. gauge and the back pressure is that of the atmosphere. If Xi = 1.0 find the three efficiencies, 771,772 and 773. Change the initial pressure only to 150 lbs. gauge and find the efficiencies. Change the initial quality to 160° F. superheat and find the efficiencies. Change the back pressure only to 27 in. and find the efficiencies.

Problem 7. —The following results were obtained from a test of an engine:

Size of engine 10 in. X 14 in. (neglect rod)

Time of test 60 min.

Clearance 7 per cent.

Number of revolutions 15,000

Steam used 3003 lbs.

Average gauge pressure at throttle 112 lbs. per sq. in.

Barometric pressure 14.7 lbs. per sq. in.

Average quality of steam 0.99

Average temperature of condensate 135° F.

Average temperature of water leaving 120° F.

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