Concept explainers
a)
The final equilibrium temperature.
a)
Answer to Problem 92P
The final equilibrium temperature is
Explanation of Solution
Write the expression for the energy balance equation for closed system.
Here, energy transfer into the control volume is
Write the expression to calculate the mass of the air.
Here, mass of the air is
Conclusion:
Substitute 0 for
Here, mass of the air is
From the Table A-2, “Ideal-gas specific heats of various common gases”, obtain the properties for air.
From the Table A-3, “Properties of common liquids, solids, and foods”, the specific heat of water
Substitute
Substitute
Thus, the final equilibrium temperature is
b)
The amount of heat transfer to the air.
b)
Answer to Problem 92P
The amount of heat transfer to the air is
Explanation of Solution
Write the expression to calculate the heat transfer
Conclusion:
Substitute
Thus, the amount of heat transfer to the air is
c)
The entropy generation.
c)
Answer to Problem 92P
The entropy generation is
Explanation of Solution
Write the expression for the entropy balance equation of the system.
Here, rate of net entropy in is
Write the expression to calculate the final pressure
Here, final temparature is
Conclusion:
Substitute
Substitute 0 for
Substitute
Thus, the entropy generation is
Want to see more full solutions like this?
Chapter 7 Solutions
THERMODYNAMICS
- In a container with a fixed volume of 0.5 m3, initially there is refrigerant -134a at a pressure of 200 kPa and a dryness fraction of 40%. Later, heat is transferred from a source at 35°C to the refrigerant until its pressure rises to 400 kPa. Calculate the entropy changes of the system, the surroundings, and the universe during the phase change.arrow_forwardtwo aluminum ingots, one weighing 1.5 kg at 450 degrees celsius while the other is 1.1 kg at 250 degrees celsius, are placed in an insulated enclosure. assuming there is no heat transfer from the ingots to the enclosure material, determine the final temperature and the entropy associated with the process.arrow_forwardStainless-steel ball bearings (ρ = 8085 kg/m3 and cp = 0.480 kJ/kg·°C) having a diameter of 1.8 cm are to be quenched in water at a rate of 1100 per minute. The balls leave the oven at a uniform temperature of 900°C and are exposed to air at 20°C for a while before they are dropped into the water. If the temperature of the balls drops to 850°C prior to quenching, determine the rate of entropy generation due to heat loss from the balls to the air.arrow_forward
- Ten grams of computer chips with a specific heat of 0.3 kJ/kg·K are initially at 20°C. These chips are cooled by placement in 5 grams of saturated liquid R-134a at –40°C. Presuming that the pressure remains constant while the chips are being cooled, determine the entropy change of the entire system. Is this process possible? Why?arrow_forwardSteam at 3 MPa and 400°C is expanded to 30 kPa in an adiabatic turbine with an isentropic efficiency of 92 percent. Determine the power produced by this turbine, in kW, when the mass flow rate is 2 kg/s.arrow_forwardA piston–cylinder device contains superheated steam. During an actual adiabatic process, the entropy of the steam will (never, sometimes, always) increasearrow_forward
- Ten grams of computer chips with a specific heat of 0.3 kJ/kg·K are initially at 20°C. These chips are cooled by placement in 5 grams of saturated liquid R-134a at –40°C. Presuming that the pressure remains constant while the chips are being cooled, determine the entropy change of the R-134a.arrow_forwardUnder what circumstances can the entropy of a system decrease for a spontaneous process?arrow_forwardIn a production facility, 1.2-in-thick, 2-ft × 2-ft square brass plates (ρ = 532.5 lbm/ft3 and cp = 0.091 Btu/lbm·°F) that are initially at a uniform temperature of 75°F are heated by passing them through an oven at 1300°F at a rate of 450 per minute. If the plates remain in the oven until their average temperature rises to 1000°F, determine the rate of entropy generation associated with this heat transfer process.arrow_forward
- Refrigerant-134a at 140 kPa and 210C is compressed by an adiabatic 1.3-kW compressor to an exit state of 700 kPa and 60C. Neglecting the changes in kinetic and potential energies, determine (a) the isentropic efficiency of the compressor, (b) the volume flow rate of the refrigerant at the compressor inlet, in L/min, and (c) the maximum volume flow rate at the inlet conditions that this adiabatic 1.3-kW compressor can handle without violating the second law.arrow_forwardAir enters the compressor of a gas-turbine plant at ambient conditions of 100 kPa and 25 °C with a low velocity and exits at 1 MPa and 347 °C with a velocity of 90 m/s. The compressor is cooled at a rate of 1500 kJ/min, and the power input to the compressor is 250 kW. Determine the mass flow rate of air through the compressor. (Hint: Use Table A-17 of the Booklet for the properties of air.)arrow_forwardWhat is entropy and its application?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