(a)
Rate at which air conditioner remove energy.
(a)
Answer to Problem 55P
The energy is
Explanation of Solution
Air conditioner removes its energy in the form of heat from the cold reservoir.
Write the equation for coefficient of performance.
Here
The efficiency is given as
Here
Divide the numerator and denominator of (II) with
Rewrite (III) in terms of
Conclusion:
Substitute
Substitute
The energy is
(b)
Power required for input work.
(b)
Answer to Problem 55P
The input work is
Explanation of Solution
Write the equation for work done by the engine
Divide (V) with
Conclusion:
Substitute
The input work is
(c)
The change in entropy.
(c)
Answer to Problem 55P
The net entropy change is
Explanation of Solution
The hot reservoir increases in entropy by
The cold reservoir decreases its entropy by
Write the equation for change in entropy
Conclusion:
Substitute
The net entropy change is
(d)
Fractional change in
(d)
Answer to Problem 55P
The fractional change is to drop by
Explanation of Solution
Using (I) find the
Then the actual
Take the ratio of
Conclusion:
Substitute
Substitute
Therefore, the fractional change is to drop by
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Chapter 18 Solutions
Principles of Physics: A Calculus-Based Text
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- Compressors powered by natural gas engines are increasing in popularity. Several major manufacturing facilities have already replaced the electric motors that drive their compressors by gas driven engines in order to reduce their energy bills since the cost of natural gas is much lower than the cost of electricity. Consider a facility that has a 130-kW compressor that runs 4400 h/yr at an average load factor of 0.6. Making reasonable assumptions and using unit costs for natural gas and electricity at your location, determine the potential cost savings per year by switching to gas-driven engines.arrow_forwardA Carnot engine operates between the temperatures Th = 100°C and Tc = 27°C. By what factor does the theoretical efficiency increase if the temperature of the hot reservoir is increased to 560°C? ec, new ec =arrow_forwardA certain Carnot engine was built in a laboratory. The lab technicians found out that if the temperature of the cold reservoir is kept at 295 K, the efficiency of the engine is 26.0%. If the hot reservoir is kept at constant temperature, at what temperature must the cold reservoir be set, so that the efficiency of the engine is increased to 33.0%?arrow_forward
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