Essential University Physics: Volume 1 (3rd Edition)
3rd Edition
ISBN: 9780321993724
Author: Richard Wolfson
Publisher: PEARSON
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Chapter 19, Problem 9FTD
To determine
To explain: Why refrigerators and heat pumps have different
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Explain why heat pumps do not work as well in very cold climates as they do in milder ones. Is the same true of refrigerators?
A heat engine running backward is called a refrigerator if its
purpose is to extract heat from a cold reservoir. The same
engine running backward is called a heat pump if its
purpose is to exhaust warm air into the hot reservoir. Heat
pumps are widely used for home heating. You can think of
a heat pump as a refrigerator that is cooling the already
cold outdoors and, with its exhaust heat QH, warming the
indoors. Perhaps this seems a little silly, but consider the
following. Electricity can be directly used to heat a home by
passing an electric current through a heating coil. This is a
direct, 100% conversion of work to heat. That is, 19.0 kW
of electric power (generated by doing work at the rate
19.0 kJ/s at the power plant) produces heat energy inside
the home at a rate of 19.0 kJ/s. Suppose that the
neighbor's home has a heat pump with a coefficient of
performance of 3.00, a realistic value. NOTE: With a
refrigerator, "what you get" is heat removed. But with a
heat pump, "what you…
If energy is always conserved, never created or destroyed, then why do most of the machines in our lives eventually stop working and have to be replaced? Explain using concepts from the textbook.
The chapters and topics based on these questions come from these concepts. (Phase Changes Thermodynamics.)
Chapter 19 Solutions
Essential University Physics: Volume 1 (3rd Edition)
Ch. 19.1 - Which of these processes is irreversible? (a)...Ch. 19.2 - The low temperature for a practical heat engine is...Ch. 19.3 - A clever engineer decides to increase the...Ch. 19.4 - In each of the following processes, does the...Ch. 19 - Could you cool the kitchen by leaving the...Ch. 19 - Prob. 2FTDCh. 19 - Should a car get better mileage in the summer or...Ch. 19 - Prob. 4FTDCh. 19 - Name some irreversible processes that occur in a...Ch. 19 - Your power company claims that electric heat is...
Ch. 19 - A hydroelectric power plant, using the energy of...Ch. 19 - A heat-pump manufacturer claims the device will...Ch. 19 - Prob. 9FTDCh. 19 - The heat Q added during adiabatic free expansion...Ch. 19 - Energy is conserved, so why cant we recycle it as...Ch. 19 - Why doesnt the evolution of human civilization...Ch. 19 - What are the efficiencies of reversible heat...Ch. 19 - A cosmic heat engine might operate between the...Ch. 19 - A reversible Carnot engine operating between...Ch. 19 - A Carnot engine absorbs 900 J of heat each cycle...Ch. 19 - Find the COP of a reversible refrigerator...Ch. 19 - Prob. 18ECh. 19 - The human body can be 25% efficient at converting...Ch. 19 - Calculate the entropy change associated with...Ch. 19 - You metabolize a 650-kcal burger at your 37C body...Ch. 19 - You heat 250 g of water from 10C to 95C. By how...Ch. 19 - Melting a block of lead already at its melting...Ch. 19 - How much energy becomes unavailable for work in an...Ch. 19 - Prob. 25ECh. 19 - A Carnot engine extracts 745 J from a 592-K...Ch. 19 - The maximum steam temperature in a nuclear power...Ch. 19 - Youre engineering an energy-efficient house that...Ch. 19 - A power plants electrical output is 750 MW....Ch. 19 - A power plant extracts energy from steam at 280C...Ch. 19 - The electric power output of all the thermal...Ch. 19 - Consider a Carnot engine operating between...Ch. 19 - An industrial freezer operates between 0C and 32C,...Ch. 19 - Use appropriate energy-flow diagrams to analyze...Ch. 19 - Prob. 35PCh. 19 - A refrigerator maintains an interior temperature...Ch. 19 - You operate a store thats heated by an oil furnace...Ch. 19 - Use energy-flow diagrams to show that the...Ch. 19 - A heat pump extracts energy from groundwater at...Ch. 19 - A reversible engine contains 0.350 mol of ideal...Ch. 19 - (a) Determine the efficiency for the cycle shown...Ch. 19 - A 0.20-mol sample of an ideal gas goes through the...Ch. 19 - A shallow pond contains 94 Mg of water. In winter,...Ch. 19 - Estimate the rate of entropy increase associated...Ch. 19 - The temperature of n moles of ideal gas is changed...Ch. 19 - The temperature of n moles of ideal gas is changed...Ch. 19 - A 6.36-mol sample of ideal diatomic gas is at 1.00...Ch. 19 - A 250-g sample of water at 80C is mixed with 250 g...Ch. 19 - An ideal gas undergoes a process that takes it...Ch. 19 - In an adiabatic free expansion, 6.36 mol of ideal...Ch. 19 - Find the entropy change when a 2.4-kg aluminum pan...Ch. 19 - An engine with mechanical power output 8.5 kW...Ch. 19 - Find the change in entropy as 2.00 kg of H2O at...Ch. 19 - Gasoline engines operate approximately on the Otto...Ch. 19 - The compression ratio r of an engine is the ratio...Ch. 19 - In a diesel cycle, gas at volume V1 and pressure...Ch. 19 - (a) Show that the heal flowing into the diesel...Ch. 19 - Youre considering buying a car that comes in...Ch. 19 - The 54-M W wood-fired McNeil Generating Station in...Ch. 19 - A 500-g copper block at 80C is dropped into 1.0 kg...Ch. 19 - An objects heat capacity is inversely proportional...Ch. 19 - A Carnot engine extracts heat from a block of mass...Ch. 19 - In an alternative universe, youve got the...Ch. 19 - Youre the environmental protection officer for a...Ch. 19 - Find an expression for the entropy gain when hot...Ch. 19 - Problem 74 of Chapter 16 provided an approximate...Ch. 19 - The molar specific heat at constant pressure for a...Ch. 19 - Prob. 68PCh. 19 - Energy-efficiency specialists measure the heat Qh...Ch. 19 - Refrigerators remain among the greatest consumers...Ch. 19 - The refrigerators COP is a. 13. b. 2. c. 3. d. 4.Ch. 19 - The fuel energy consumed at the power plant to run...Ch. 19 - Prob. 73PP
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- Show that the coefficients of performance of refrigerators and heat pumps are related by COPref=COPhp1. Start with the definitions of the COP s and the conservation of energy relationship between Qh, QC, and W.arrow_forward(h) Figure Ql.(h) below shows the emission of steam from a kettle causing a pinwheel to turn. Which of the laws of thermodynamics best explains this phenomenon? Justify your answer. Figure Q1.(h)arrow_forwardHow much kinetic energy would I have to generate by rubbing my hands together to light my hands on fire? Utilize an equation that relates to thermodynamics to answer this question.arrow_forward
- The second law of thermodynamics states that heat by itself flows only from bodies of higher temperature to bodies of lower temperature. If a refrigerator transfers heat from the cold cooling coils to the warm surroundings, does this not violate the stated law? Explain.arrow_forwardWhat is the basic idea behind a refrigerator? It sucks in cold air from the room and pumps it into the food compartment. It makes cold air and injects it into the food compartment. It removes heat from the compartment and pumps it to the outside.arrow_forwardA heat engine is 25% efficient. if the engine does 500 joules of work per cycle, how much energy is lost to the exhaust per cyclearrow_forward
- You can't take warm water, turn it into ice, and use the heat from the water to run an engine. This is an example of which law of thermodynamics?arrow_forwardYou put heat energy into your car and it does not work . The difference between what you put in and the work it does is the change in internal energy of your car's "system." This is an example of which law of thermodynamics?arrow_forwardA heat pump that is used to heat a house has a COP of 2.5. That is, the heat pump delivers 2.5 kWh of energy to the house for each 1 kWh of electricity it consumes. Is this a violation of the first law of thermodynamics? Explain.arrow_forward
- It is well known that the thermal efficiency of heat engines increases as the temperature of the energy source increases. In an attempt to improve the efficiency of a power plant, somebody suggests transferring heat from the available energy source to a higher-temperature medium by a heat pump before energy is supplied to the power plant. What do you think of this suggestion? Explain.arrow_forwardA heat engine takes in 2500J and does 1500J of work. a) How much energy is expelled as waste? b) What is the efficiency of the engine?arrow_forwardA heat pump is a device that absorbs energy from the cold outdoor air and transfers it to the warmer indoors. Is this a violation of the second law of thermodynamics? Explain.arrow_forward
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