JNTU, B.Tech ,I-Semester

Thermodynamics

, November 2008

(Mechanical Engineering and Automobile Engineering)

SET-2

1. (a) Explain thermodynamic system, surroundings and universe, illustrate the same

with examples.

(b) Distinguish between closed system, open system and isolated system with suitable examples.

2. A system receives 200 kj of heat at constant volume process and rejects 220 kj of

heat at constant pressure and 40 kj of work is done on the system. The system is brought to its original state by an adiabatic process calculate the adiabatic work. If the initial internal energy is 240 kj, then calculate the value of internal energy at all points.

3. (a) Enunciate the two classical statements of second law of thermodynamics.

(b) One kg of water is heated at a constant pressure of 0.7 MPa. The boiling point is 164.970C and the latent heat of evaporation is 2066.3 kJ/kg. If the initial temperature of water is 00C, find the increase in entropy of the water if the final state is dry saturated steam. Assume for liquid water Cp = 4.2 kJ/kgK.

4. (a) Explain third law of Thermodynamics.

(b) A tank holds 1 kg of air at 100 kPa, 400C, and another tank holds 1 kg of air at 200 kPa, 400C. The atmosphere is at 100 kPa, 200C. In which tank is the stored energy is greater? Determine the availability of the air in each tank.

5. (a) A gas expands according to the law pvn = constant If p1, v1 are the intial conditions as regards pressure and volume respectively and r is the ratio of expansion, show that the work done by gas during the changes is equal to p1 v1n?1 [1 ? 1(r)n?1 ]and that the heat received by the gas is equal to?n?1×p1v1n?1 [1 ? 1(r)n?1 ] Where ? is the ratio of the specific heat of the gas.

(b) 0.28m3 of air at pressure 7bar expand to 1.4m3. The final pressure is 1.26 bar. Assuming the expansion to the polytropic, calculate the heat supplied and change of internal energy. Take ? = 1.4

6. A rigid tank of volume 1.2m3 is divided into two equal parts by a partition. One

compartment contains neon gas at 200C and 110kPa and other contains argon gas

at 470C and 225kPa. Now partition is removed and the two gases are allowed to mix. If 10kJ of heat is lost to the surroundings at 200C during the mixing process, determine the final temperature and pressure of the mixture.

7. (a) Discuss with the help of graphs the variation of air standard efficiency of an

Otto cycle with compression ratio and adiabatic index.

(b) For air standard diesel cycle the following data are available:

Compression ratio = 16.

Heat added / Kg = 2500 kJ/Kg.

Lowest temperature in the cycle = 3000 K.

Lowest pressure in the cycle = 1 bar.

Calculate

i. Pressure and temperature at each point in the cycle

ii. Thermal efficiency.

8. Draw the line diagram of the Bell-Coleman refrigeration cycle retrigesetion. Explain with the help of a P-V diagram, different processes in the cycle. Explain its advantages and disadvantages.