Fundamentals Of Engineering Thermodynamics
9th Edition
ISBN: 9781119391388
Author: MORAN, Michael J., SHAPIRO, Howard N., Boettner, Daisie D., Bailey, Margaret B.
Publisher: Wiley,
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Chapter 2, Problem 2.69P
To determine
The rate at which energy is removed by heat transfer from the room and the cost of operating the air conditioner for 24 hours.
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An air conditioner operating at steady state maintains a dwelling at 20°C on a day when the outside temperature is 40°C. Energy is removed by heat transfer from the dwelling at a rate of 3200 J/s while the air conditioner’s power input is 0.8 kW.
Determine the coefficient of performance of the air conditioner.
Determine the power input required by a reversible refrigeration cycle providing the same cooling effect while operating between hot and cold reservoirs at 40°C and 20°C, respectively, in kW.
A heat pump with a coefficient of performance of 3.5 provides energy at an average rate of 70,000 kJ/h to maintain a building at 20 deg C on a day when the outside temperature is -5 deg C. If electricity costs 8.5 cents per kWh,
(a) determine the actual operating cost and the minimum theoretical operating cost, each in $/day.
(b) compare the results of part (a) with the cost of electrical-resistance heating.
An air conditioner operating at steady state maintains a dwelling at 20 C on a day when the outside
temperature is 35 C. Energy is removed by heat transfer from the dwelling at a rate of 2800 J/s while the
air conditioner's power input is 0.8 kw.
(a) Determine the coefficient of performance of the air conditioner.
(b) Determine the power input required if it was a Carnot refrigerator.
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Chapter 2 Solutions
Fundamentals Of Engineering Thermodynamics
Ch. 2 - Prob. 2.1ECh. 2 - Prob. 2.2ECh. 2 - Prob. 2.3ECh. 2 - Prob. 2.4ECh. 2 - Prob. 2.5ECh. 2 - Prob. 2.6ECh. 2 - Prob. 2.7ECh. 2 - Prob. 2.8ECh. 2 - Prob. 2.9ECh. 2 - Prob. 2.10E
Ch. 2 - Prob. 2.11ECh. 2 - Prob. 2.12ECh. 2 - Prob. 2.13ECh. 2 - Prob. 2.14ECh. 2 - Prob. 2.15ECh. 2 - Prob. 2.16ECh. 2 - Prob. 2.17ECh. 2 - Prob. 2.1CUCh. 2 - Prob. 2.2CUCh. 2 - Prob. 2.3CUCh. 2 - Prob. 2.4CUCh. 2 - Prob. 2.5CUCh. 2 - Prob. 2.6CUCh. 2 - Prob. 2.7CUCh. 2 - Prob. 2.8CUCh. 2 - Prob. 2.9CUCh. 2 - Prob. 2.10CUCh. 2 - Prob. 2.11CUCh. 2 - Prob. 2.12CUCh. 2 - Prob. 2.13CUCh. 2 - Prob. 2.14CUCh. 2 - Prob. 2.15CUCh. 2 - Prob. 2.16CUCh. 2 - Prob. 2.17CUCh. 2 - Prob. 2.18CUCh. 2 - Prob. 2.19CUCh. 2 - Prob. 2.20CUCh. 2 - Prob. 2.21CUCh. 2 - Prob. 2.22CUCh. 2 - Prob. 2.23CUCh. 2 - Prob. 2.24CUCh. 2 - Prob. 2.25CUCh. 2 - Prob. 2.26CUCh. 2 - Prob. 2.27CUCh. 2 - Prob. 2.28CUCh. 2 - Prob. 2.29CUCh. 2 - Prob. 2.30CUCh. 2 - Prob. 2.31CUCh. 2 - Prob. 2.32CUCh. 2 - Prob. 2.33CUCh. 2 - Prob. 2.34CUCh. 2 - Prob. 2.35CUCh. 2 - Prob. 2.36CUCh. 2 - Prob. 2.37CUCh. 2 - Prob. 2.38CUCh. 2 - Prob. 2.39CUCh. 2 - Prob. 2.40CUCh. 2 - Prob. 2.41CUCh. 2 - Prob. 2.42CUCh. 2 - Prob. 2.43CUCh. 2 - Prob. 2.44CUCh. 2 - Prob. 2.45CUCh. 2 - Prob. 2.46CUCh. 2 - Prob. 2.47CUCh. 2 - Prob. 2.48CUCh. 2 - Prob. 2.49CUCh. 2 - Prob. 2.50CUCh. 2 - Prob. 2.51CUCh. 2 - Prob. 2.52CUCh. 2 - Prob. 2.53CUCh. 2 - Prob. 2.54CUCh. 2 - Prob. 2.1PCh. 2 - Prob. 2.2PCh. 2 - Prob. 2.3PCh. 2 - Prob. 2.4PCh. 2 - Prob. 2.5PCh. 2 - Prob. 2.6PCh. 2 - Prob. 2.7PCh. 2 - Prob. 2.8PCh. 2 - Prob. 2.9PCh. 2 - Prob. 2.10PCh. 2 - Prob. 2.11PCh. 2 - Prob. 2.12PCh. 2 - Prob. 2.13PCh. 2 - Prob. 2.14PCh. 2 - Prob. 2.15PCh. 2 - Prob. 2.16PCh. 2 - Prob. 2.17PCh. 2 - Prob. 2.18PCh. 2 - Prob. 2.19PCh. 2 - Prob. 2.20PCh. 2 - Prob. 2.21PCh. 2 - Prob. 2.22PCh. 2 - Prob. 2.23PCh. 2 - Prob. 2.24PCh. 2 - Prob. 2.25PCh. 2 - Prob. 2.26PCh. 2 - Prob. 2.27PCh. 2 - Prob. 2.28PCh. 2 - Prob. 2.29PCh. 2 - Prob. 2.30PCh. 2 - Prob. 2.31PCh. 2 - Prob. 2.32PCh. 2 - Prob. 2.33PCh. 2 - Prob. 2.34PCh. 2 - Prob. 2.35PCh. 2 - Prob. 2.36PCh. 2 - Prob. 2.37PCh. 2 - Prob. 2.38PCh. 2 - Prob. 2.39PCh. 2 - Prob. 2.40PCh. 2 - Prob. 2.41PCh. 2 - Prob. 2.42PCh. 2 - Prob. 2.43PCh. 2 - Prob. 2.44PCh. 2 - Prob. 2.45PCh. 2 - Prob. 2.46PCh. 2 - Prob. 2.47PCh. 2 - Prob. 2.48PCh. 2 - Prob. 2.49PCh. 2 - Prob. 2.50PCh. 2 - Prob. 2.51PCh. 2 - Prob. 2.52PCh. 2 - Prob. 2.53PCh. 2 - Prob. 2.54PCh. 2 - Prob. 2.55PCh. 2 - Prob. 2.56PCh. 2 - Prob. 2.57PCh. 2 - Prob. 2.58PCh. 2 - Prob. 2.59PCh. 2 - Prob. 2.60PCh. 2 - Prob. 2.62PCh. 2 - Prob. 2.63PCh. 2 - Prob. 2.64PCh. 2 - Prob. 2.65PCh. 2 - Prob. 2.66PCh. 2 - Prob. 2.67PCh. 2 - Prob. 2.68PCh. 2 - Prob. 2.69PCh. 2 - Prob. 2.70PCh. 2 - Prob. 2.71P
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- A heat pump maintains a dwelling at 68°F. When operating steadily, the power input to the heat pump is 5 hp, and the heat pump receives energy by heat transfer from 55°F well water at a rate of 500 Btu/min. (a) Determine the coefficient of performance. (b) Evaluating electricity at $0.18 per kWh, determine the cost of electricity in a month when the heat pump operates for 300 hours. Part A Determine the coefficient of performance. y = iarrow_forwardA heat pump cycle delivers energy by heat transfer to a dwelling at a rate of 40,000 Btu/h. The coefficient of performance of the cycle is 3.8. (a) Determine the power input to the cycle, in hp. (b) Evaluating electricity at $0.085 per kW · h, determine the cost of electricity during the heating season when the heat pump operates for 2000 hours. сycle i hp Cost = $ iarrow_forwardA system executes a power cycle while receiving 750 kJ by heat transfer at a temperature of 1500 K and discharging 100 kJ by heat transfer at a temperature of 500 K. Another heat transfer from the system occurs at a temperature of 1000 K. Determine the thermal efficiency if cycle 0.1 kJ/K. Q3 T3 = 1000 K Q₁ = 750 kJ Q₂ = 100 kJ T₁ = 1500 K Wcycle T₂ = 500 K =arrow_forward
- At steady state, a refrigeration cycle operates between hot and cold reservoirs at 300K and 275K respectively. The refrigerator removes 600 kW of heat from the cold reservoir. If the cycle's coefficient of performance is 4, determine the power input required in kW. Compare this with the minimum theoretical power required in kW.arrow_forwardDuring transient state operation, a gearbox receives 60 kW through the input shaft and delivers power through the output shaft. For the gearbox as the system, the rate of energy transfer by convection isQ T = −hA (Tb – Tf)where h = 0.171 kW/m 2 ⋅⋅ K is the heat transfer coefficient, A = 1.0 m 2 is the outer surface area of the gearbox, Tb = 300 K (27°C) is the temperature at the outer surface, and Tf = 293 K (20°C) is the temperature of the surrounding air away from the immediate vicinity of the gearbox. The rateof specific internal energy is 5kJ/Kg. For the gearbox, evaluate the heat transfer rate and the power delivered through the output shaft, each in kW.arrow_forwardA heat pump maintains a dwelling at 68°F. When operating steadily, the power input to the heat pump is 3 hp, and the heat pump receives energy by heat transfer from 55°F well water at a rate of 500 Btu/min. (a) Determine the coefficient of performance. (b) Evaluating electricity at $0.18 per kW · h, determine the cost of electricity in a month when the heat pump operates for 300 hours.arrow_forward
- Kelvin-Planck statement defines the Second law of thermodynamics as a. It is impossible to construct a machine that will operate in a cycle, extract heat from a reservoir, and do an equivalent amount of work on the surroundings. b. It is impossible to construct a device that operates in a cycle and produces no effect other than the transfer of heat from a lower-temperature body to a higher-temperature body. c. It is possible to construct a device that operates in a cycle and produces no effect other than the transfer of heat from a lower-temperature body to a higher-temperature body. d. It is possible to construct a machine that will operate in a cycle, extract heat from a reservoir, and do an equivalent amount of work on the surroundings.arrow_forwardBy supplying energy to a house at a rate of 25,000 kJ/hr, a heat pump maintains the temperature of the dwelling at 20 C when the outside air is at -10 C. If electricity costs 8 cents per kW-hr, determine the minimum theoretical operating cost to heat the house for 24 hours. $1.97 O $1.37 $1.75 O $1.51 O$1.64arrow_forwardA window air conditioner that consumes 1 kW of electricity when running and has a coefficient of performance of 3 is placed in the middle of a room and is plugged in. The rate of cooling or heating this air conditioner will provide to the air in the room when running is (a) 3 kJ/s, cooling (b) 1 kJ/s, cooling (c) 0.33 kJ/s, heating (d) 1 kJ/s, heating (e) 3 kJ/s, heatingarrow_forward
- 1. In an analysis, a heat engine based on the Carnot cycle operating between 1000 0C and 300 0C. The heat rejected from this engine to the sink was at a rate of 800 kJ/min. Determine the thermal efficiency (in %) and power output (in kW) of the engin 2.You found out that the power output of your dream car is the same as the sum of each digits of your student number (in kW) with a percentage thermal efficiency the same as the first four digit of your student number divided by 100. The calorific value of the fuel available has a calorific value of 40 000 kJ/kg. Assuming a constant power output from the car, calculate the heat transfer rate (in kW) and the fuel consumption rate (in kg/h)arrow_forwardAn air conditioner is a device used to cool the inside of a home. It is, in essence, a refrigerator in which mechanical work is done and heat removed from the (cooler) inside and rejected to the (warmer) outside. A home air conditioner operating on a reversible Carnot cycle between the inside, absolute temperature T2, and the outside, absolute tempera- ture T1 > T2, consumes P joules/sec from the power lines when operating continuously. (a) In one second, the air conditioner absorbs Q2 joules from the house and rejects Q1 joules outdoors. Develop a formula for the efficiency ratio Q2/P in terms of T1 and T2. (b) Heat leakage into the house follows Newton's law Q = A(T, – T2). Develop a formula for T, in terms of T1, P, and A for continuous operation of the air conditioner under constant outside temperature T and uniform (in space) inside temperature T2. (c) The air conditioner is controlled by the usual on-off thermostat and it is observed that when the thermostat set at 20°C and an…arrow_forward1. Is a temperature difference necessary to operate a heat engine? State why or why not. 2. Definitions of efficiency vary depending on how energy is being converted. Compare the definitions of efficiency for the human body and heat engines. How does the definition of efficiency in each relate to the type of energy being converted into doing work? 3. Why-other than the fact that the second law of thermodynamics says reversible engines are the most efficient-should heat engines employing reversible processes be more efficient than those employing irreversible processes? Consider that dissipative mechanisms are one cause of irreversibility. 1. (a) What is the efficiency of a cyclical heat engine in which 75.0 kJ of heat transfer occurs to the environment for every 95.0 kJ of heat transfer into the engine? (b) How much work does it produce for 100 k) of heat transfer into the engine? 2. The engine of a large ship does 2.00×10°J of work with an efficiency of 5.00%. (a) How much heat…arrow_forward
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