A commercial refrigerator with refrigerant-134a as the working fluid is used to keep the refrigerated space at −35°C by rejecting waste heat to cooling water that enters the condenser at 18°C at a rate of 0.25 kg/s and leaves at 26°C. The refrigerant enters the condenser at 1.2 MPa and 50°C and leaves at the same pressure subcooled by 5°C. If the compressor consumes 3.3 kW of power, determine (a) the mass flow rate of the refrigerant, (b) the refrigeration load, (c) the COP, and (d) the minimum power input to the compressor for the same refrigeration load.
FIGURE P6–107
(a)
The mass flow rate of the refrigerant.
Answer to Problem 101P
The mass flow rate of the refrigerant is
Explanation of Solution
Determine the rate of heat transferred to the water.
Here, the mass flow rate of the water is
Determine the mass flow rate of a refrigerant.
Conclusion:
From the Table A-13, “Superheated refrigerant R-134a” obtain the value of enthalpy of the refrigerant at the inlet of the condenser at the 1.2 MPa of pressure and
From the Table A-13, “Superheated refrigerant R-134a” obtain the value of temperature of the refrigerant at the inlet of the condenser at the 1.2 MPa of pressure as,
Calculate the exit temperature of the refrigerant in the condenser.
Here, the temperature leave from the condenser is
Substitute
Refer to Table A-11, “Saturated refrigerant R-134a”, obtain the below exit enthalpy of the condenser at compressed liquid state on the basis of exit temperature of
Write the formula of interpolation method of two variables.
Here, the variables denote by x and y are temperature and enthalpy of vaporization.
Show the temperature at
S. No |
Temperature, |
enthalpy of vaporization |
1 | ||
2 | ||
3 |
Calculate exit enthalpy of the condenser at compressed liquid state on the basis of exit temperature of
Substitute
From above calculation the exit enthalpy of the condenser at compressed liquid state on the basis of exit temperature of
Repeat the above Equation (IV) to obtain the value of enthalpy of saturated liquid that entering the inlet of the condenser at the
Repeat the above Equation (IV) to obtain the value of enthalpy of saturated liquid which is leaving the condenser at the
Substitute
Substitute
Thus, the mass flow rate of the refrigerant is
(b)
The refrigeration load of the refrigerator.
Answer to Problem 101P
The refrigeration load of the refrigerator is
Explanation of Solution
Determine the refrigeration load of the refrigerator.
Here, the power input consumed by compressor is
Conclusion:
Substitute
Thus, the refrigeration load of the refrigerator is
(c)
The COP of a reversible refrigerator operating between the same temperature limits.
Answer to Problem 101P
The COP of a reversible refrigerator operating between the same temperature limits is
Explanation of Solution
Determine the coefficient of performance of the refrigerator.
Conclusion:
Substitute
Thus, the COP of a reversible refrigerator operating between the same temperature limits is
(d)
The minimum power input to the compressor.
Answer to Problem 101P
The minimum power input to the compressor is
Explanation of Solution
Determine the maximum coefficient of performance of the reversible refrigerator operating between the same temperature limits.
Here, the temperature of higher temperature body is
Determine the minimum power input to the condenser for the same refrigerator load.
Conclusion:
Substitute
Substitute
Thus, the minimum power input to the compressor is
Want to see more full solutions like this?
Chapter 6 Solutions
Package: Thermodynamics: An Engineering Approach With 2 Semester Connect Access Card
- A commercial refrigerator with refrigerant-134a as the working fluid is used to keep the refrigerated space at –35°C by rejecting waste heat to cooling water that enters the condenser at 18°C at a rate of 0.25 kg/s and leaves at 26°C. The refrigerant enters the condenser at 1.2 MPa and 50°C and leaves at the same pressure subcooled by 5°C. If the compressor consumes 3.3 kW of power, determine the minimum power input to the compressor for the same refrigeration load.arrow_forwardRefrigerant-134a enters the compressor of a refrigerator at 0.14MPa and -10°C at a rate of 0.05 kg/s and leaves at 0.8 MPa and 50°C. The refrigerant is cooled in the condenser to 26°C and 0.72 MPa and is throttled to 0.15 MPa. Determine (a) the rate of heat removal from the refrigerated space and the power input to the compressor, (b) the isentropic efficiency of the compressor, and (c) the coefficient of performance of the refrigerator. Answers: (a) 7.93 kW, 2.02 kW, (b) 0.939, (c) 3.93arrow_forwardConsider a refrigeration system using refrigerant-134a as the working fluid. If this refrigerator is to operate in an environment at 20°C, what is the minimum pressure to which the refrigerant should be compressed? Why?arrow_forward
- A commercial refrigerator with refrigerant-134a as the working fluid is used to keep the refrigerated space at -35°C by rejecting waste heat to cooling water that enters the condenser at 18°C at a rate of 0.25 kg/s and leaves at 26°C. The refrigerant enters the condenser at 1.2 MPa and 50°C and leaves at the same pressure subcooled by 5°C. If the compressor consumes 3.3 kW of power, determine (a) the mass flow rate of the refrigerant, (b) the refrigeration load, (c) the COP, and (d) the minimum power input to the compressor for the same refrigeration load.arrow_forwardAn air conditioner using refrigerant-134a as the working fluid is used to keep the temperature of a room at 23°C by giving heat to the external environment at 37°C. The heat gain of the house from the walls and windows is 250 kJ/min; 900 W heat is emitted into the room from the computer, TV and lamps. The refrigerant enters the compressor with a flow rate of 100 L/min in the form of saturated vapor at 400 kPa pressure and leaves the compressor at 70°C at 1200 kPa pressure.a) Draw the cycle by showing the elements of the cycle.b) the actual COP value,c) The highest COP value,d) The smallest refrigerant can have for the same compressor inlet and outlet conditions.Calculate the volumetric flow.arrow_forwardA commercial refrigerator with refrigerant-134a as the working fluid is used to keep the refrigerated space at –30°C by rejecting its waste heat to cooling water that enters the condenser at 18°C at a rate of 0.25 kg/s and leaves at 26°C. The refrigerant enters the condenser at 1.2 MPa and 65°C and leaves at 42°C. The inlet state of the compressor is 60 kPa and –34°C and the compressor is estimated to gain a net heat of 450 W from the surroundings. Determine the theoretical maximum refrigeration load for the same power input to the compressor. Water 26°C ↑ 18°C 1.2 MPа 42°C 65°C Condenser Expansion Win valve Evaporator Compressor 60 kPa -34°Carrow_forward
- Refrigerant-134a at a rate of 0.08 kg/s enters the compressor of a refrigerator as superheated vapor at 0.18 MPa and 0 ℃ and leaves at 0.9 MPa and 80 ℃. The refrigerant is cooled in the condenser to 31.3 ℃ and 0.8 MPa and it is throttled to 0.18 MPa. Disregarding any heat transfer and pressure drops in the connecting lines between the components, Determine the adiabatic efficiency of the compressorarrow_forwardA refrigerated room is kept at −18◦C by a vapor-compression cycle with R-134a as the refrigerant. Heat is rejected to cooling water that enters the condenser at 14◦C at a rate of 0.35 kg/s and leaves at 22◦C. The refrigerant enters the condenser at 1.2MPa and 50◦C and leaves at the same pressure subcooled by 5◦C. If the compressor consumes 5.5 kW of power, determine (a) the mass flow rate of the refrigerant, (b) the refrigeration load and the COP, (c) the second-law efficiency of the refrigerator and the total exergy destruction in the cycle, and (d) the exergy destruction in the condenser. Take specific heat of water to be 4.18 kJ/kg·◦C.arrow_forwardRefrigerant-134a enters the compressor of a refrigerator at 140 kPa and -10°C at a rate of 0.3 m3/min and leaves at 1 MPa. The isentropic efficiency of the compressor is 78 percent. The refrigerant enters the throttling valve at 0.95 MPa and 30°C and leaves the evaporator as saturated vapor at -18.5°C. Show the cycle on a T-s diagram with respect to saturation lines, and determine (a) the power input to the compressor, (b) the rate of heat removal from the refrigerated space, and (c) the pressure drop andrate of heat gain in the line between the evaporator and the compressor. answers 1.88 kW, 7.11 kW, 1.72 kPa, 0.24 kWarrow_forward
- Consider a refrigrator that operates on the vapor compression refrigeration cycle with R-134a as the working fluid. The refrigerant enters the compressor as saturated vapor at 70 kPa, and exits at 1200 kPa and 90°C, and leaves the condenser as saturated liquid at 1200 kPa. The coefficient of performance of this refrigrator isarrow_forwardA refrigerator uses R-134a as the working fluid and operates on an ideal vapor compression cycle between 0.14 MPa and 0.8 MPa. If the mass flow rate of the refrigerant is 0.06 kg/s, determine (a) the rate of heat removal from the refrigerated space, (b) the power input to the compressor, (c) the heat rejection rate in the condenser, and (d) the COP.arrow_forwardA commercial refrigerator using R-134a as a refrigerant is used to keep the cooled environment at -35 C. The refrigerator releases the waste heat to the cooling water that enters the condenser at 18 C at 0.25 kg / s and leaves the condenser at 26 C. The refrigerant enters the condenser at a pressure of 1.2 MPa and a temperature of 50 ° C, and leaves the condenser at the same pressure, supercooled at 5 ° C. Since the compressor consumes 3.3 kW of power, a) Mass flow rate of the refrigerant, b) Cooling load and COP value c) Calculate the minimum power consumed by the compressor for the same cooling load.arrow_forward
- Elements Of ElectromagneticsMechanical EngineeringISBN:9780190698614Author:Sadiku, Matthew N. O.Publisher:Oxford University PressMechanics of Materials (10th Edition)Mechanical EngineeringISBN:9780134319650Author:Russell C. HibbelerPublisher:PEARSONThermodynamics: An Engineering ApproachMechanical EngineeringISBN:9781259822674Author:Yunus A. Cengel Dr., Michael A. BolesPublisher:McGraw-Hill Education
- Control Systems EngineeringMechanical EngineeringISBN:9781118170519Author:Norman S. NisePublisher:WILEYMechanics of Materials (MindTap Course List)Mechanical EngineeringISBN:9781337093347Author:Barry J. Goodno, James M. GerePublisher:Cengage LearningEngineering Mechanics: StaticsMechanical EngineeringISBN:9781118807330Author:James L. Meriam, L. G. Kraige, J. N. BoltonPublisher:WILEY