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Chapter 21: Q. 16 (page 595)
How much heat is exhausted to the cold reservoir by the heat engine shown in ?
The heat exhausted to the cold reservoir by heat engine,
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A refrigerator using helium gas operates on the reversed cycle shown in FIGURE. What are the refrigerator’s () coefficient of performance and () power input if it operates at cycles per second?
The engine that powers a crane burns fuel at a flame temperature of 2000°C. It is cooled by 20°C air. The crane lifts a 2000 kg steel girder 30 m upward. How much heat energy is transferred to the engine by burning fuel if the engine is 40% as efficient as a Carnot engine?
The FIGURE shows the Diesel cycle. It is similar to the Otto cycle (see Problem), but there are two important differences. First, the fuel is not admitted until the air is fully compressed at point . Because of the high temperature at the end of 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 constant-pressure process. The cycle shown, for one cylinder of a diesel engine, has a displacement localid="1650278379201" of localid="1650278390412" and a compression ratio localid="1650278397535" These are typical values for a diesel truck. The engine operates with intake air localid="1650278425123" at localid="1650278430754" and localid="1650278435051" pressure. The quantity of fuel injected into the cylinder has a heat of combustion of localid="1650278440305" .
. Find , , and at each of the four corners of the cycle. Display your results in a table.
. What is the network done by the cylinder during one full cycle?
. What is the thermal efficiency of this engine?
. What is the power output in kW and horsepower of an eight-cylinder diesel engine running at ?
FIGURE Pis the diagram of Example , but now the device is operated in reverse.
a. During which processes is heat transferred into the gas?
b. Is this, heat extracted from a hot reservoir, or , heat extracted from a cold reservoir? Explain.
c. Determine the values ofand.
Hint: The calculations have been done in Example and do not need to be repeated. Instead, you need to determine which processes now contribute to and which to .
d. Is the area inside the curve or ? What is its value?
e. The device is now being operated in a ccw cycle. Is it a refrigerator? Explain.
Do the energy-transfer diagrams inrepresent possible refrigerators? If not, what is wrong?
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