Concept explainers
A refrigeration system uses a water-cooled condenser for rejecting the waste heat. The system absorbs heat from a space at 25°F at a rate of 21,000 Btu/h. Water enters the condenser at 65°F at a rate of 1.45 lbm/s. The COP of the system is estimated to be 1.9. Determine (a) the power input to the system in kW, (b) the temperature of the water at the exit of the condenser in °F, and (c) the maximum possible COP of the system. The specific heat of water is 1.0 Btu/bm·°F.
(a)
The power input of the refrigerator.
Answer to Problem 129RP
The power input of the refrigerator is
Explanation of Solution
Determine coefficient of performance to the refrigerator.
Here, the power consumption of the refrigerator is
Conclusion:
Substitute
Thus, the power input of the refrigerator is
(b)
The exit temperature of the water.
Answer to Problem 129RP
The exit temperature of the water is
Explanation of Solution
Determine rate of heat rejected in the rejected of the refrigerator.
Here, the power consumption of the refrigerator is
Determine exit temperature of the water.
Here, the mass rate of the water is
Conclusion:
Substitute
Substitute
Thus, the exit temperature of the water is
(c)
The maximum possible COP of the refrigerator.
Answer to Problem 129RP
The maximum possible COP of the refrigerator is
Explanation of Solution
Determine the average temperature of the water as source temperature.
Determine maximum possible COP of the refrigerator.
Here, the system absorb heat from a space is
Conclusion:
Substitute
Substitute
Thus, the maximum possible COP of the refrigerator is
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Chapter 6 Solutions
Thermodynamics: An Engineering Approach
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