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Unformatted text preview: PHYS 153 Homework 6A Problem 1 The ﬁgure below shows a Carnot heat engine driving a Carnot refrigerator. (a) Determine Q1, Q2, Q3, and Q4. (b) Is Q3 greater than, less than, or equal to Q1? (c) Do these two devices, when operated together in this way, violate the second law?
Explain. PHYS 153 Homework 6A Problem 2 A heat engine uses a diatomic gas that follows the pV cycle in the ﬁgure below. (a) Determine the pressure, volume, and temperature at point 1. (b) Determine AUth, l'VS, and Q for each of the three processes. Put your results in a table
for easy reading. (c) How much work does this engine do per cycle and what is its thermal efﬁciency? V (\2 P03 PHYS 153 Homework 6A Problem 3 A 0.0500 kg cube of ice at an initial temperature of —15 °C is placed in 0.600 kg of water at
T = 45.0 °C in an insulated container of negligible mass. (a) Calculate the ﬁnal temperature
of the water once the ice has melted. (b) Calculate the Change in entropy of the system. PHYS 153 Homework 6A Problem 4 A heat engine with 0.20 11101 of a monatomic ideal gas initially ﬁlls a 2000 c1113 cylinder at
600 K. The gas goes through the following closed cycle: 0 Isothermal expansion to 4000 c1113.
0 Isochoric cooling to 300 K.
s o Isothermal compression to 2000 c111: . o Isochoric heating to 600 K. How much work does this engine do per cycle and what is its thermal efﬁciency? PHYS 153 Homework 6A Problem 5 The ﬁgure below shows the Diesel cycle. It is similar to the Otto cycle, but there are two
important differences. F irst, the fuel is not admitted until the air is fully compressed at point
2. Because of the high temperature at the end of an adiabatic compression, the fuel begins
to burn spontaneously. (There are no spark plugs in a diesel engine!) Second, combustion
takes place more slowly, with fuel continuing to be injected. This makes the ignition stage
a constantpressure process. The cycle shown, for one cylinder of a. diesel engine, has a
displacement VnmX — Vmin of 1000 cm3 and a compression ratio 'r = Vnmx/Vmin = 21. These
are typical values for a diesel truck. The engine operates with intake air (of = 1.40) at
25 °C and 1.0 atm pressure. The quantity of fuel injected into the cylinder has a heat of
combustion of 1000 J. (a) Find 1), V, and T at each of the four corners of the cycle. Display your results in a
table. (b) What is the net work done by the cylinder during on full cycle? (c) What is the thermal efﬁciency of this engine? (d) What is the power output in kW and horsepower (1 hp 2 746 W ) of an eightcylinder
diesel engine running at 2400 rpm? germ) Ga 0: a on
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 Spring '08
 Witt
 Heat engine, 15 °C, 25 °C, 1 hp, 0.600 kg, 2 746 W

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