Topics: First Law of Thermodynamics, SFEE, flow work, Steam, Second Law of Thermodynamics
Total Marks: 30.
Time: 1 hr and 30 min
SECTION A: Attempt all the questions 2x3 = 6
1) What is sub-cooled or undercooled water?
2) What is degree of superheat in case of superheated steam?
3) Write the first law of thermodynamics for a open process.
SECTION B: Attempt all the questions 3x3 = 9
1) 2 kg of saturated water at 8 bar pressure has been supplied 4700 kJ of heat. Find the end condition of the steam produced. Also find the value of specific internal energy and specific entropy of the steam.
2) A stream of air with a mass rate 0.6 kg/s enters a nozzle at a pressure of 8 bar and temperature 200°C at a velocity 1.2 m/s. If the final pressure at exit is 0.3 MPa, then find the value of velocity at exit and inlet and outlet/exit diameter of the nozzle.
3) A heat engine running between two thermal reservoirs of 800 K and 300 K is used to power a refrigerator running between two thermal reservoirs of 325 K and 260 K. If the heat engine draws 5000 kJ heat from reservoirs at 800 K, then find the amount of heat extracted from 260 K reservoir by the refrigerator.
SECTION C: Attempt any three questions 5x3 = 15
1) What is flow work? Distinguish between flow work and non-flow work. Find the expression for flow work in a open system. What is SFEE?
2) What is quality of steam? Explain the terms "dryness fraction" and "wetness fraction". Calculate the specific enthalpy of steam at 9 bar pressure and 350°C temperature.
3) What will be the quality of the steam at the end of adiabatic expansion of steam at 12 bar pressure and 400°C to 1.2 bar in a turbine. Also, find the ideal work out put by the turbine.
4) Explain the second law of thermodynamics. Prove that both the statements of 2nd law of thermodynamics are equivalent to each other.
5) Explain the following terms.
ii) Saturated Liquid Line,
iv) Saturation Temperature,
v) Reversible Heat Engine
SOLUTIONS
Topics: First Law of Thermodynamics, SFEE, flow work, Steam, Second Law of Thermodynamics
Total Marks: 30.
Time: 1 hr and 30 min
SECTION A: Attempt all the questions 2x3 = 6
1) What is sub-cooled or undercooled water?
Ans: The boiling point of water is a function of the pressure, as pressure increases, boiling point is also elevated. For a certain pressure, water has a fixed boiling temperature known as saturation temperature and denoted by ts. If the temperature of water at a given pressure is lower than the corresponding saturation temperature i.e. t < ts, then the water is called sub-cooled or under-cooled water.
2) What is degree of superheat in case of superheated steam?
3) Write the first law of thermodynamics for a open process.
SECTION B: Attempt all the questions 3x3 = 9
1) 2 kg of saturated water at 8 bar pressure has been supplied 4700 kJ of heat. Find the end condition of the steam produced. Also find the value of specific internal energy and specific entropy of the steam.
2) A stream of air with a mass rate 0.6 kg/s enters a nozzle at a pressure of 8 bar and temperature 200°C at a velocity 1.2 m/s. If the final pressure at exit is 0.3 MPa, then find the value of velocity at exit and inlet and outlet/exit diameter of the nozzle.
3) A heat engine running between two thermal reservoirs of 800 K and 300 K is used to power a refrigerator running between two thermal reservoirs of 325 K and 260 K. If the heat engine draws 5000 kJ heat from reservoirs at 800 K, then find the amount of heat extracted from 260 K reservoir by the refrigerator.
SECTION C: Attempt any three questions 5x3 = 15
1) What is flow work? Distinguish between flow work and non-flow work. Find the expression for flow work in a open system. What is SFEE?
2) What is quality of steam? Explain the terms "dryness fraction" and "wetness fraction". Calculate the specific enthalpy of steam at 9 bar pressure and 350°C temperature.
3) What will be the quality of the steam at the end of adiabatic expansion of steam at 12 bar pressure and 400°C to 1.2 bar in a turbine. Also, find the ideal work out put by the turbine.
4) Explain the second law of thermodynamics. Prove that both the statements of 2nd law of thermodynamics are equivalent to each other.
5) Explain the following terms.
ii) Saturated Liquid Line,
iv) Saturation Temperature,
v) Reversible Heat Engine
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