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Chapter 1 Basic Concepts 1.A gas in a piston-cylinder device is compressed, and as a result its temperature rises. Is this a heat or work interaction?

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Presentation on theme: "Chapter 1 Basic Concepts 1.A gas in a piston-cylinder device is compressed, and as a result its temperature rises. Is this a heat or work interaction?"— Presentation transcript:

1 Chapter 1 Basic Concepts 1.A gas in a piston-cylinder device is compressed, and as a result its temperature rises. Is this a heat or work interaction? 2.On a P-v diagram, what does the area under the process curve represent? 3.Determine the energy required to accelerate a 2000-kg car from 20 to 70 km/h on an uphill road with a vertical rise of 40m.

2 4. Consider a device with one inlet and one exit. If the volume flow rates at the inlet and at the exit are the same, is the flow through the device necessarily steady ? Why? 5. A 2 m 3 rigid tank contains nitrogen gas at 500kPa and 300K. Now heat is transferred to the nitrogen in the tank and the pressure of nitrogen rises to 800kPa. The work done during this process is (A) 600 kJ (B) 1000 kJ (C) 0 kJ (D) 500 kJ (E) 1600 kJ

3 6. A 2 m 3 rigid tank contains nitrogen gas at 500kPa and 300K. Now heat is transferred to the nitrogen in the tank and the pressure of nitrogen rises to 800kPa. The work done during this process is (A) 600 kJ (B) 1000 kJ (C) 0 kJ (D) 500 kJ (E) 1600 kJ

4 CHAPTER 2 PROPERTIES OF PURE SUBSTANCES 2.1 A rigid tank contains 5kg of an ideal gas at 4atm and 40 ℃.Now a valve is opened, and half of mass of the gas is allowed to escape.If the final pressure in the tank is 1.5atm.the final temperature in the tank is [a] -38 ℃ [b]30 ℃ [c]40 ℃ [d] 53 ℃ [e]144 ℃ 2.2 A rigid vessel contains steam at 20 MPa and 400 ℃.The mass of the steam is [a] 5.0kg [b] 0.322kg [c] 322kg [d] 503kg [e]680kg

5 2.3 A rigid tank is filled with saturated liquid-vapor mixture of water at 200kPa.If 20 percent of the mass is liquid and the 80 percent of the mass is vapor,the total mass in the tank is [a] 705kg [b] 500kg [c]258kg [d] 635kg [e]2809

6 Chapter 3 The first Law of Thermodynamics  A reversible cycle plots as a perfect circle on a T-S diagram with maximum and minimum temperatures 600 K and 300K and a maximum and minimum entropy of 600 kJ/K and 300kJ/K.

7 a) What is the net work of this cycle? b) Indicate the path in the cycle along which heat is rejected. How do you know?(A sentence or two is required, perhaps bolstered by an equation). c) What is the thermodynamic efficiency of this cycle?

8  2. The sketch below shows a perfectly insulated container with two compartments separated by a non-adiabatic, frictionless piston. Both compartments are at the same pressure (P A = P B ) and contain an equal amount of the same gas ( m A =m B ). Initially compartment A is at a higher temperature than compartment B(T A >T B ).

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10  a) Which way, if at all, does the piston move? Indicate by an arrow on a drawing in your exam book (A sentence or two is expected, perhaps bolstered by some equations).  b) Is the final internal energy U final of the system (both compartments together) lower, equal or higher than initial internal energy U initial of the system? Why? (A sentence or two is expected, perhaps bolstered by some equations.)

11  c) What is the final temperature of the system T final expressed in terms of T A and T B ?  b) What is the change in entropy of compartment A? What is the change in entropy of compartment B?  e) What is the change in entropy of the surroundings?  f) Is this process reversible or irreversible? How do you know? (Note: you do not have to prove your answer mathematically to get full credit. Explain in a sentence how you know whether the process is reversible or irreversible)

12  10 kg of air contained in a piston cylinder apparatus at 5 bar,300K, expands isothermally until the pressure is 1 bar. Determine:  (i) the work done.  (ii) the internal energy change of the air.  (iii) the heat transfer.  Assume that air behaves as an ideal gas and pressure variation is gradual and continuous.

13  A system is capable of executing a cyclic process as indicated in the P V sketch; it may be executed either clockwise abca or counterclockwise adca. (a) When going clockwise to state c, 80KJ of heat flow from the system. Find the work along the path ca. (b) When going counterclockwise to state c, 70KJ of heat flow from the system. Find the work during the process adc.

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15 CHAPTER 5 THE SECOND LAW OF THERMODYNAMICS 5.1 The drinking water needs of an office are met by cooling tab water in a refrigerated water fountain from 22 ℃ to 8 ℃ at an average rate of 8kg/h.If the COP of this refrigerator is 3.1,the required power input to this refrigerator is [a] 28W [b] 42W [c] 88W [d] 130W [e] 403W

16 5.2 A heat engine cycle is executed with steam in the saturation dome. The pressure of steam 1MPa during heat addition, and 0.5MPa during heat rejection. The highest possible efficiency of this heat engine is [a] 6.2 % [b] 15.6 % [c] 50.0 % [d] 93.8 % [e] 100 %

17 5.3 A heat engine receives heat from a source at 100 ℃ and rejects the waste heat to a sink at 50 ℃.If heat is supplied to this engine at a rate of 100kj/s,the maximum power this heat engine can produce is [a] 25.4kW [b] 55.4kW [c] kW [d] 95.0kW [e] 100.0kW

18 5.4 Steam is compressed from 8 MPa and 300 ℃ to 10 MPa isentropically. The final temperature of the steam is [a] 290 ℃ [b] 300 ℃ [c] 320 ℃ [d] 330 ℃ [e] 340 ℃

19 5.5 Helium gas is compressed from 1 atm and 25 ℃ to a pressure of 10 atm adiabatically. The lowest temperature of helium after compression is [a] 25 ℃ [b] 63 ℃ [c] 250 ℃ [d] 384 ℃ [e] 476 ℃

20 5.6 Steam expands in an adiabatic turbine from 10MPa and 500 ℃ to 0.1MPa at a rate of 8kg/s.If steam leaves the turbine as saturated vapor,the power output of the turbine is [a] 5586kw [b] 698kw [c] 2136 kw [d] 12,452kw [e]26,990kw

21 5.7 A unit mass of a substance an irreversible process from state 1 to state 2 while gaining heat from the surroundings at temperature T in the amount of q.If the entropy of the substance is at state 1,and at state 2,the entropy change of the substance s during this process is [a] [b] [c] [d] [e]

22 5.8 Air is compressed from room conditions to a specified pressure in a reversible manner by two compressor :one isothermal and the other adidbatic. If the entropy change of air s during the reversible adiabatic compression, the correct statement regarding entropy change of air per unit mass is [a] [b] [c] [d] [e]

23 5.9 Heat is lost through a plane wall steadily at a rate of 600W.If the inner and outer surface temperature of the wall are 20 ℃ and5 ℃, respectively, the rate of entropy generation within the wall is [a] 0.11W/K [b] 4.21W/K [c] 2.10 W/K [d] 142.1W/K [e] 90.0W/K

24 5.10 Air at 15 ℃ is compressed steadily and isothermally from 100KPa to700 KPa at a rate of 0.12kg/s.The minimum power input to the compressor is [a] 1.0kW [b] 11.2kW [c] 25.8kW [d] 19.3 kW [e] 16.1kW

25 5.11 Air is to be compressed steadily and isentropically from 1atm to 16atm by a two-stage compressor. To minimize the total compression work, the intermediate pressure between the two stages must be [a] 2atm [b] 4atm [c] 8 atm [d] 10 atm [e] 12atm

26 5.12 Liquid water enters an adiabatic piping system at 15 ℃ at a rate of 5kg/s.If the water temperature rises by 0.5 ℃ during flow due to friction.the rate of entropy generation in the pipe is [a] 36W/K [b] 29 W/K [c] 685W/K [d] 920W/K [e] 8370W/K

27 5.13 Steam enters an adiabatic turbine at 4 MPa and 500 ℃ at a rate of 15kg/s,and exits at 0.2MPa and 300 ℃.The rate of entropy generation in the turbine is [a] 0.8kW/K [b] 1.2kW/K [c] 12.0kW/K [d] 15.1kW/K [e] 17.4kW/K

28 5.13  A quantity of air undergoes a thermodynamic cycle consisting of three processes in series.  Process 1-2: constant-volume heating from P1=0.1 MPa, T 1 =288 K, V 1 =0.02 to P 2 =0.42 MPa;  Process 2-3: constant-pressure cooling ;  Process 3-1: isothermal heating to the initial state ;  Employing the ideal gas model with Cp=1 kJ/kgK, evaluate the change in entropy for each process. Sketch the cycle on p-v coordinates.

29 CHAPTER 8 THERMODYNAMICS OF HIGH-SPEED GAS FLOW 8.1 In which medium will sound travel fastest for a given temperature: air,helium,or argon? 8.2 Is it possible to accelerate a gas to a supersonic velocity in a converging nozzle? 8.3 Air enters a converging-diverging nozzle at a pressure of 1.2MPa with negligible velocity. What is the lowest pressure that can be obtained at the throat of the nozzle?

30 8.4 Air enters a nozzle at 0.2MPa,350K,and a velocity of 150m/s.Assuming isentropic flow, determine the pressure and temperature of air at a location where the air velocity equals the velocity of sound. What is the ratio of the area at this location to the entrance area? 8.5 Air enters a converging-diverging nozzle at 0.8MPa with negligible velocity. Assuming the flow to be isentropic, determine the back pressure that will result in an exit Mach number of 1.8.

31 Air enters an adiabatic nozzle at 800 K and 140 KPa and emerges at 7 KPa. The isentropic efficiency of the nozzle is known to be Determine the discharge velocity. Sketch the process on a T-S diagram and label the states. You may assume the working fluid is a perfect gas with Cp=1 kJ/kgK.

32 8.6 Steam enters an converging nozzle at 30.MPa and 600 ℃ with a negligible velocity, and it exits at 1.8MPa.For a nozzle exit area of 24c ㎡,determine the exit. Velocity, mass flow rate, and exit Mach number if the nozzle (a) is isentropic and (b) has an efficiency of 90percent

33 CHAPTER 9 GAS POWER CYCLES 9.1 A Carnot cycle operates between the temperature limits of 300K and 1500K,and produces 600kw of net power. The rate of entropy change of the working fluid during the heat addition process is [a] 0 [b] 0.4kW/K [c] 0.5 kW/K [d] 2.0kW/K [e] 5.0kW/K

34  a ) A simple engine uses a perfect gas as the working fluid in a piston-cylinder system. The gas is first heated at constant pressure from state 1 to state 2, then cooled at constant volume to state 3 where T3=T1, and then cooled at constant temperature, thereby returning to state 1. Derive expressions for the amounts of energy transfer as work and heat (per kg of gas) for each process in terms of the temperatures and pressures at each state and the constants of the gas. Suppose T 1 =300K, P 1 =0.2 MPa, T 2 =800K, K=Cp/Cv=1.4. Calculate the cycle efficiency (net work output/energy input as heat)

35  b ) When the engine of part (a) is reversed, it becomes a refrigeration device. Calculate the amount of energy transfer as heat from the cold space for this cycle (per kg of gas), and the cycle COP (energy transfer as heat from cold space/net work input). You can assume air for the working fluid.

36 CHAPTER 10 REFRIGERATION CYCLES 10.1 A refrigerator removes heat from a refrigerated space at-5 ℃ at a rate of 0.35kj/s and rejects it to an environment at 20 ℃.The minimum requires power input is [a] 30W [b] 33W [c] 56W [d] 124W [e] 350W

37 10.2 An ideal vapor compression refrigeration cycle with R-134a as the working fluid operates between the pressure limits of 140kPa and 900kpa.The mass fraction of the refrigerant that is in the liquid phase at the inlet of the evaporator is [a] 0.75 [b] 0.65 [c] 0.50 [d] 0.35 [e] 0.25

38 10.3 Consider a refrigeration that operates on the vapor compression refrigerant cycle with R-134a as the working fluid. The refrigerant enters the compressor as saturated vapor at 140kPa,and exits at 800kPa and 60 ℃,and leaves the condenser as saturated liquid at 800kPs.The coefficient of performance of this refrigerator is [a] 0.41 [b] 0.1 [c] 1.8 [d] 2.5 [e] 3.4

39  There are 528 kJ/min of heat removed from a body by a refrigerator operating between the limits of K and K. If its coefficient of performance is three fourths of that of a Carnot refrigerator working between the same temperature limits, find (a) the heat rejected and (b) the work input, kw. (c) What are the COP and the heat if this device is used to deliver heat ?


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