Thermodynamics: An Engineering Approach
9th Edition
ISBN: 9781260048766
Author: CENGEL
Publisher: MCG
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Chapter 6.11, Problem 94P
In an effort to conserve energy in a heat-engine cycle, somebody suggests incorporating a refrigerator that will absorb some of the waste energy QL and transfer it to the energy source of the heat engine. Is this a smart idea? Explain.
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A heat pump operates with a Coefficient of Performance equal to 8. What is the COP if this cycle were to operate as a refrigerator?
Since Lucas is an engineer familiar with
thermodynamics. He decided to create his own
heat engine at home to avoid paying for
electricity. He created a small, makeshift heat
engine for trial. The combustion of his fuel.
diesel, reaches a temperature of 750°C, while
waste heat is disposed to the atmosphere at
50°C.
He, then connected a generator and a heat
pump to the heat engine to check the amount
of power being produced. Assume that the
heat pump will be used to warm his room to
25°C, while the outside temperature is at 5°C.
Lucas' rooms loses 85,000 kJ/hr of heat. And,
25% of the heat engine's power output goes to
the heat pump. How much diesel (in kg) needs
to be burned by the heat engine to maintain the
temperature in Lucas' room? Assume carnot
heat engine and heat pump. If the natural gas
has a heating value of 22,000 BTU/lb.
Prove that if you had a heat engine whose efficiency was better than the ideal value (4.5), you could hook it up to an ordinary Carnot refrigerator to make a refrigerator that requires no work input.
Chapter 6 Solutions
Thermodynamics: An Engineering Approach
Ch. 6.11 - A mechanic claims to have developed a car engine...Ch. 6.11 - Describe an imaginary process that violates both...Ch. 6.11 - Describe an imaginary process that satisfies the...Ch. 6.11 - Describe an imaginary process that satisfies the...Ch. 6.11 - An experimentalist claims to have raised the...Ch. 6.11 - Consider the process of baking potatoes in a...Ch. 6.11 - Prob. 7PCh. 6.11 - What are the characteristics of all heat engines?Ch. 6.11 - What is the KelvinPlanck expression of the second...Ch. 6.11 - Is it possible for a heat engine to operate...
Ch. 6.11 - Does a heat engine that has a thermal efficiency...Ch. 6.11 - In the absence of any friction and other...Ch. 6.11 - Are the efficiencies of all the work-producing...Ch. 6.11 - Baseboard heaters are basically electric...Ch. 6.11 - Consider a pan of water being heated (a) by...Ch. 6.11 - A heat engine has a total heat input of 1.3 kJ and...Ch. 6.11 - A steam power plant receives heat from a furnace...Ch. 6.11 - A heat engine has a heat input of 3 104 Btu/h and...Ch. 6.11 - A 600-MW steam power plant, which is cooled by a...Ch. 6.11 - A heat engine with a thermal efficiency of 45...Ch. 6.11 - A heat engine that propels a ship produces 500...Ch. 6.11 - A steam power plant with a power output of 150 MW...Ch. 6.11 - An automobile engine consumes fuel at a rate of 22...Ch. 6.11 - Solar energy stored in large bodies of water,...Ch. 6.11 - A coal-burning steam power plant produces a net...Ch. 6.11 - An Ocean Thermal Energy Conversion (OTEC) power...Ch. 6.11 - Prob. 27PCh. 6.11 - Prob. 29PCh. 6.11 - What is the difference between a refrigerator and...Ch. 6.11 - Prob. 31PCh. 6.11 - Define the coefficient of performance of a...Ch. 6.11 - Define the coefficient of performance of a heat...Ch. 6.11 - Prob. 34PCh. 6.11 - A refrigerator has a COP of 1.5. That is, the...Ch. 6.11 - In a refrigerator, heat is transferred from a...Ch. 6.11 - A heat pump is a device that absorbs energy from...Ch. 6.11 - What is the Clausius expression of the second law...Ch. 6.11 - Show that the KelvinPlanck and the Clausius...Ch. 6.11 - The coefficient of performance of a residential...Ch. 6.11 - A food freezer is to produce a 5-kW cooling...Ch. 6.11 - An automotive air conditioner produces a 1-kW...Ch. 6.11 - A food refrigerator is to provide a 15,000-kJ/h...Ch. 6.11 - Prob. 44PCh. 6.11 - Determine the COP of a heat pump that supplies...Ch. 6.11 - Prob. 46PCh. 6.11 - A heat pump with a COP of 1.4 is to produce a...Ch. 6.11 - An air conditioner removes heat steadily from a...Ch. 6.11 - A household refrigerator that has a power input of...Ch. 6.11 - When a man returns to his well-sealed house on a...Ch. 6.11 - Water enters an ice machine at 55F and leaves as...Ch. 6.11 - A refrigerator is used to cool water from 23 to 5C...Ch. 6.11 - A household refrigerator runs one-fourth of the...Ch. 6.11 - Consider an office room that is being cooled...Ch. 6.11 - A house that was heated by electric resistance...Ch. 6.11 - Refrigerant-134a enters the condenser of a...Ch. 6.11 - Refrigerant-134a enters the evaporator coils...Ch. 6.11 - An inventor claims to have developed a resistance...Ch. 6.11 - Prob. 60PCh. 6.11 - Why are engineers interested in reversible...Ch. 6.11 - A cold canned drink is left in a warmer room where...Ch. 6.11 - A block slides down an inclined plane with...Ch. 6.11 - Prob. 64PCh. 6.11 - Prob. 65PCh. 6.11 - Show that processes that use work for mixing are...Ch. 6.11 - Why does a nonquasi-equilibrium compression...Ch. 6.11 - Prob. 68PCh. 6.11 - Prob. 69PCh. 6.11 - What are the four processes that make up the...Ch. 6.11 - Prob. 71PCh. 6.11 - Prob. 72PCh. 6.11 - Prob. 73PCh. 6.11 - Somebody claims to have developed a new reversible...Ch. 6.11 - Is there any way to increase the efficiency of a...Ch. 6.11 - Consider two actual power plants operating with...Ch. 6.11 - You are an engineer in an electric-generation...Ch. 6.11 - Prob. 78PCh. 6.11 - A thermodynamicist claims to have developed a heat...Ch. 6.11 - A heat engine is operating on a Carnot cycle and...Ch. 6.11 - A completely reversible heat engine operates with...Ch. 6.11 - An inventor claims to have developed a heat engine...Ch. 6.11 - A Carnot heat engine operates between a source at...Ch. 6.11 - A heat engine is operating on a Carnot cycle and...Ch. 6.11 - A heat engine operates between a source at 477C...Ch. 6.11 - An experimentalist claims that, based on his...Ch. 6.11 - In tropical climates, the water near the surface...Ch. 6.11 - Prob. 89PCh. 6.11 - Prob. 90PCh. 6.11 - Prob. 91PCh. 6.11 - Prob. 92PCh. 6.11 - How can we increase the COP of a Carnot...Ch. 6.11 - In an effort to conserve energy in a heat-engine...Ch. 6.11 - Prob. 95PCh. 6.11 - Prob. 96PCh. 6.11 - A thermodynamicist claims to have developed a heat...Ch. 6.11 - Determine the minimum work per unit of heat...Ch. 6.11 - Prob. 99PCh. 6.11 - An air-conditioning system operating on the...Ch. 6.11 - A heat pump operates on a Carnot heat pump cycle...Ch. 6.11 - An air-conditioning system is used to maintain a...Ch. 6.11 - A Carnot refrigerator absorbs heat from a space at...Ch. 6.11 - Prob. 104PCh. 6.11 - A Carnot refrigerator operates in a room in which...Ch. 6.11 - Prob. 106PCh. 6.11 - A commercial refrigerator with refrigerant-134a as...Ch. 6.11 - Prob. 108PCh. 6.11 - A heat pump is to be used for heating a house in...Ch. 6.11 - A completely reversible heat pump has a COP of 1.6...Ch. 6.11 - A Carnot heat pump is to be used to heat a house...Ch. 6.11 - A Carnot heat engine receives heat from a...Ch. 6.11 - Prob. 113PCh. 6.11 - Derive an expression for the COP of a completely...Ch. 6.11 - Calculate and plot the COP of a completely...Ch. 6.11 - Prob. 116PCh. 6.11 - Prob. 117PCh. 6.11 - Prob. 118PCh. 6.11 - Someone proposes that the entire...Ch. 6.11 - Prob. 120PCh. 6.11 - Prob. 121PCh. 6.11 - Prob. 122PCh. 6.11 - It is commonly recommended that hot foods be...Ch. 6.11 - It is often stated that the refrigerator door...Ch. 6.11 - Prob. 125RPCh. 6.11 - Prob. 126RPCh. 6.11 - Prob. 127RPCh. 6.11 - A Carnot heat pump is used to heat and maintain a...Ch. 6.11 - A refrigeration system uses a water-cooled...Ch. 6.11 - A refrigeration system is to cool bread loaves...Ch. 6.11 - A heat pump with a COP of 2.8 is used to heat an...Ch. 6.11 - Prob. 132RPCh. 6.11 - Consider a Carnot heat-engine cycle executed in a...Ch. 6.11 - Prob. 134RPCh. 6.11 - Consider a Carnot refrigeration cycle executed in...Ch. 6.11 - Prob. 137RPCh. 6.11 - Consider two Carnot heat engines operating in...Ch. 6.11 - A heat engine operates between two reservoirs at...Ch. 6.11 - An old gas turbine has an efficiency of 21 percent...Ch. 6.11 - Prob. 141RPCh. 6.11 - Prob. 142RPCh. 6.11 - Prob. 143RPCh. 6.11 - The drinking water needs of a production facility...Ch. 6.11 - Prob. 145RPCh. 6.11 - Prob. 147RPCh. 6.11 - Prob. 148RPCh. 6.11 - Prob. 149RPCh. 6.11 - Prob. 150RPCh. 6.11 - Prob. 151RPCh. 6.11 - A heat pump with refrigerant-134a as the working...Ch. 6.11 - Prob. 153RPCh. 6.11 - Prob. 155RPCh. 6.11 - Prob. 156RPCh. 6.11 - Prob. 157RPCh. 6.11 - Prove that a refrigerators COP cannot exceed that...Ch. 6.11 - Consider a Carnot refrigerator and a Carnot heat...Ch. 6.11 - A 2.4-m-high 200-m2 house is maintained at 22C by...Ch. 6.11 - A window air conditioner that consumes 1 kW of...Ch. 6.11 - The drinking water needs of an office are met by...Ch. 6.11 - The label on a washing machine indicates that the...Ch. 6.11 - A heat pump is absorbing heat from the cold...Ch. 6.11 - A heat engine cycle is executed with steam in the...Ch. 6.11 - A heat pump cycle is executed with R134a under the...Ch. 6.11 - A refrigeration cycle is executed with R-134a...Ch. 6.11 - A heat pump with a COP of 3.2 is used to heat a...Ch. 6.11 - A heat engine cycle is executed with steam in the...Ch. 6.11 - A heat engine receives heat from a source at 1000C...Ch. 6.11 - An air-conditioning system operating on the...Ch. 6.11 - A refrigerator is removing heat from a cold medium...Ch. 6.11 - Two Carnot heat engines are operating in series...Ch. 6.11 - A typical new household refrigerator consumes...
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- Since Lucas is an engineer familiar with thermodynamics. He decided to create his own heat engine at home to avoid paying for electricity. He created a small, makeshift heat engine for trial. The combustion of his fuel, diesel, reaches a temperature of 750°C, while waste heat is disposed to the atmosphere at 50°C.He, then connected a generator and a heat pump to the heat engine to check the amount of power being produced. Assume that the heat pump will be used to warm his room to 25°C, while the outside temperature is at 5°C. Lucas’ rooms loses 85,000 kJ/hr of heat. And, 25% of the heat engine’s power output goes to the heat pump. How much diesel (in kg) needs to be burned by the heat engine to maintain the temperature in Lucas’ room? Assume carnot heat engine and heat pump. If the natural gas has a heating value of 22,000 BTU/lb. *Round off all answers to four decimal places*arrow_forwardComment on the importnace of quickly returning the milk carton to the refrigerator for an energy conservation point of view.arrow_forwardA heat pump supplied heat to a residential house having an average temperature of 32 °C. The heat pump receives heat from a lake that has an average temperature of 9 °C as shown in Figure Q2. Lake water Lake water Člost Lake water inlet to HP heat pump exchanger, HP Lake, House Lake water exit in Figure Q2 heat pump arrangement (a) Evaluate the Carnot cycle efficiency (b) If the house loses heat to the atmosphere at the rate of 56000 kJ/h, determine the minimum power supplied to the heat pump, in kW. (c) A heat exchanger is used to transfer the energy from the lake water to the heat pump. If the lake water temperature decreases by 5°C as it flows through the lake water-to-heat pump heat exchanger, determine the minimum mass flow rate of lake water, in kg/s. Neglect the effect of the lake water pump. Show all steps of your calculations clearlyarrow_forward
- What would be the maximum COP for a heat pump operating in your house if the outside temperature is 55 F? Draw a heat flow diagram. How much cheaper will this be than electrical heating?arrow_forwardTrue or false Heat is transferred to a system by either a cheap commercially available air-sourced heat pump with coefficient of performance of just 1.5, or an expensive 100% efficient electrical resistance heater. The loss of Carnot Work Potential (Exergy destruction, or T0Sloss term) is minimum when heat is added by the cheap commercial heat pump. Heat is transferred to a system by either a cheap commercially available air-sourced heat pump with coefficient of performance of just 1.5, or an expensive 100% efficient isothermal heat source. The loss of Carnot Work Potential (Exergy destruction, or T0Sloss term) is minimum when heat is added by the isothermal heat source.arrow_forwardData are provided for two reversible refrigeration cycles. One cycle operates between hot and cold reservoirs at 27°C and 3°C, respectively. The other cycle operates between the same hot reservoir at 27°C and a cold reservoir at -35°C. The refrigerator removes the same amount of energy by heat transfer from its cold reservoir. Determine the ratio of the net work input values of the two cycles, WCycle,2 Wcycle,1arrow_forward
- A heat pump operates with Refrigerant 134a as the working fluid. You are required to analyze its performance, and compare it with Camot heat pump. The data of the heat pump is as under: 23 - Thermodynamies-II Page 1 of 3 The heat pump is presently providing heating at a rate of 12 kW to maintain the interior of a building at 20°C. Outside temperature is 5°C. The refrigerant enters the compressor at 2.4 bar and increases the pressure to 8.0 bar. Efficiency of the compressor is 80%. a Temperatures at the principal states of the cycle, each °C b. Power input to the compressor, in kW c. Coefficient of performance Relate its performance with the specifications provided by the vendor i.e. COP = 8.5 and identify the possible reasons of differences. Draw Ts diagramarrow_forward(b) An irreversible heat pump with COP of 2.4 is used to heat water to 80°C for cleaning purposes. This heat pump absorbs heat from surrounding at 30°C and received the entire power, W from a Carnot heat engine operating between 250°C and 30°C. The Carnot heat engine received 6.3 kW of heat from the high temperature source. i) Draw the schematic diagram of the above system. ii) Determine the power received by the heat pump, W from Carnot heat engine, kW. iii) Calculate the rate of heat supplied to the water by the heat pump, kW. iv) Determine the COP of the heat pump if it operates on a reversed Carnot cycle.arrow_forwardA heat engine operates on a Carnot cycle with an efficiency of 75 percent. What COP would a refrigerator operating on the same cycle have? The low temperature is 0°C.arrow_forward
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