B.Tech II Year I Semester Examinations, December - 2018

THERMODYNAMICS

(Mechanical Engineering)

Time: 3 hours Max. Marks: 75

Note: This question paper contains two parts A and B.

Part A is compulsory which carries 25 marks. Answer all questions in Part A. Part B consists of 5 Units. Answer any one full question from each unit. Each question carries 10 marks.

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PART- A (25 Marks)

1. Define the following:
   1. Thermodynamic system. [2M]
   2. Quasi-static process. [3M]
   3. Carnot theorem. [2M]
   4. Clausius statement of II law. [3M]
   5. Available energy. [2M]

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   6. Helmholtz function. [3M]
   7. Law of corresponding states. [2M]
   8. Dalton’s law of partial pressure. [3M]

PART- B (50 Marks)

UNIT-I

1. 2.a) Discuss microscopic and macroscopic viewpoints of thermodynamics. [5M] b) A gas of mass 1.5 kg undergoes a quasi-static expansion which follows a relationship p = a + bV, where a and b are constants. The initial and final pressures are 1000 kPa and 200 kPa respectively and the corresponding volumes are 0.20 m³ and 1.20 m³. Calculate the work done by the gas. [5M]

   OR

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2. 3.a) Explain the conditions for reversibility of a process. [5M] b) A housewife keeps the door of a refrigerator open to cool her kitchen on a hot summer day. Would you advise her to do so? Give reasons. [5M]

UNIT-II

1. 4.a) Show that the violation of the Kelvin-Plank statement leads to the violation of the Clausius statement. [5M] b) A reversible engine operates between temperatures T₁ and T. The energy rejected by this engine is received by a second reversible engine at temperature T. The second engine rejects energy at temperature T₂. Show that T is the arithmetic mean of T₁ and T₂ if the engines deliver the same amount of work. [5M]

   OR

2. 5.a) What do you understand by the entropy principle? [5M] b) A 50 kg iron block at 500 K and a 40 kg copper block at 300 K are thrown into a large lake that is at a temperature of 285 K. Thermal equilibrium is established after a while. Assuming specific heat of iron and copper as 0.45 kJ/kg.K and 0.385 kJ/kg.K, determine the entropy change for the iron and copper blocks and the entropy change for the lake. [5M]

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UNIT-III

1. 6.a) Describe the Maxwell relations and their importance in thermodynamics. [5M] b) Derive an expression for Clausius-Clapeyron equation. [5M]

   OR

2. 7.a) What do you understand by the Joule-Thomson coefficient? [5M] b) Determine the change in the freezing point of water when the pressure is increased by 100 atm. Assume: v_ice = -1.96 x 10^-4 m³/kg, v_water = 1.00 x 10^-3 m³/kg. Latent heat of fusion = 335 kJ/kg. [5M]

UNIT-IV

1. 8.a) Explain the following:
   1. Dryness fraction
   2. Saturated liquid

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   3. Superheated vapor
   [5M] b) Steam at 2 MPa and 300 °C expands isentropically in a turbine to 0.1 MPa. Determine:
   1. The quality of steam at the end of expansion
   2. The turbine work.
   [5M]

   OR

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2. 9.a) Discuss the various methods used for measurement of steam quality. [5M] b) Draw the phase equilibrium diagram for a pure substance on T-s coordinates with relevant constant property lines. [5M]

UNIT-V

1. 10.a) Explain the following:
   1. Amagat’s law
   2. Adiabatic mixing of ideal gases.
   [5M] b) A gas mixture consists of 3 kg of oxygen, 5 kg of nitrogen and 8 kg of carbon dioxide. Determine:
   1. The mass fraction of each component
   2. The mole fraction of each component

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   3. Average molecular mass of the mixture
   4. Gas constant of the mixture.
   [5M]

   OR

2. 11.a) Explain the Kay’s rule. [5M] b) A tank of 0.5 m³ volume contains air at 25 °C and 600 kPa. A valve is opened, allowing air to escape until the pressure inside reaches 300 kPa. Determine the mass of air that has escaped from the tank. Assume that the expansion is isothermal. [5M]

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