# Thermodynamics Assignment

Intern um Larsen and Toubro Limited
19. Jan 2011
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### Thermodynamics Assignment

• 1. 1. (a) What is a System ? What is the difference between a Closed and Open System ? (b) What is a Cycle ? (c) Explain the concept of Thermodynamic Equilibrium. (d) What is a Quasi-Static Process ? What is its characteristic feature ? 2. A turbine is supplied with steam at a gauge pressure of 1.4 MPa. After expansion in the turbine, the steam flows into a condenser which is maintained at a vacuum of 710 mm of Hg. The barometric pressure is 772mm Hg. Express the inlet and exhaust steam pressures in Pascal (absolute).Take the density of mercury as 13.6 X 103kg/m3. (ANS : 1.503 MPa & 8.27 kPa) 3. What is Zeroth Law of Thermodynamics ? Explain its thermodynamic significance. 4. (a) What do you mean by positive and negative work interactions ? (b) What is Path Function and Point Function ? (c) Explain : “Heat is a Path Function and not Property.” 5. A piston and cylinder machine containing a fluid system has a stirring device in the cylinder. The piston is frictionless and is held down against the fluid due to atmospheric pressure of 101.325 kPa. The stirring device is turned 10000 revolutions with an average torque against the fluid of 1.275 N-m. Meanwhile the piston of 0.6 m diameter moves out 0.8 m. Find the net work transfer for the system. (ANS : -57.1 kJ) 6. (a) Explain the First Law of Thermodynamics. (b) Which is the Property introduced by the First Law ? 7. When a system is taken from state a to state b, in figure shown, c b along path acb, 84 kJ of heat flows into the system and the system does 32 kJ of work. (a) How much will the heat that flows into the system along path adb be, if the work done is 10.5 kJ? (ANS : 62.5 kJ) (b) When the system is returned from b to a along the curved a d path, the work done on the system is 21 kJ. Does the system absorb or liberate heat, and how much of the heat is absorbed or liberated? (ANS : -73 kJ) 8. (a) What is the difference between Work and Heat ? (b) What is Thermal Reservoir ? Define the terms ‘Source’ and ‘Sink’. (c) Give the Statements of Second Law of Thermodynamics. (d) How does a Heat Pump differ from a Refrigerator ? (e) Can you use the same device as Heat Pump in winter and Refrigerator in summer ? Explain. 9. (a) A domestic food freezer maintains a temperature of -15 oC. The ambient air temperature is 30 oC. If the heat leaks into the freezer at a continuous rate of 1.75 kJ/s what is the least power necessary to pump this heat out continuously? (ANS : 0.31 kW) (b) A cyclic heat engine operates between a source temperature of 800 oC and a sink temperature of 30 oC. What is the least rate of heat rejection per kW net output of the engine? (ANS : 0.392 kW)