JNTU PAPERS

JNTU, B.Tech ,I-Semester

Thermodynamics

November 2008

(Mechanical Engineering and Automobile Engineering)

SET-4

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. [8+8]

2. In a vessel 10 kg of oxygen is heated in a reversible, non flow, constant volume

process so that the pressure of oxygen is increased two times that of the initial value. The initial temperature is 20oC. Calculate

(a) the final temperature,

(b) the change in internal energy,

(c) the change in enthalpy and

(d) the heat transfer. Take R = 0.259 kj / kg K and Cv = 0.652 kj / kg K for oxygen. [16]

3. (a) Prove: perpetual motion machine of the second kind is impossible.

(b) Three cubic metres of air at a pressure of 1bar and a temperature of 200 C is compressed reversible and adiabatically to 4.5 bar. The same mass is then expanded is othermally to the original volume. Calculate the final pressure of the air, work done and the total entropy change. For air Cp= 1.005 kJ/kg.K and R = 0.287J/kg.K (10) [6+10]

4. (a) A pressure vessel has a volume of 1m3 and contains air at 1.4 MPa, 1750C. The

air is cooled to 250C by heat transfer to the surroundings at 250C. Calculate the availability in the initial and final states and the irreversibility for the process. Assume for air Cp= 1.005 kJ/kg.K and R = 0.287kJ/kg.K.

(b) What is third law of thermodynamics? State its significance. [10+6]

5. (a) One Kg – mole of Oxygen undergoes a reversible non – flow isothermal

compression and the volume decreases from 0.15m3/Kg to 0.06m3 /Kg and the initial temperature is 500 C. The gas obeys VanderWaal’s equation during the compression Find:

i. The work done during the process

ii. The Final pressure.

(b) Determine the pressure of air at 2050 C having a specific volume of 0.00315m3/Kg

by means of:

i. Ideal gas equation

ii. Vander Waal?s equation. [8+8]

6. (a) Methane at 150kPa, 200C enters an insulated mixing chamber at a rate of

1.0kg/s .It is mixed with air at 150kPa and 1800 C in an air methane mass ratio of 15:1. The flow is steady and kinetic energy changes are negligible. Ambient pressure and temperature are 100kPa 150C. Determine:

i. The temperature of the mixture leaving the chamber and

ii. The irreversibility of the mixing per kg of methane.

(b) How gravimetric analysis can be compared with volumetric analysis? [10+6]

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. [6+10]

8. (a) Discuss the effect of sub cooling on C.O.P. would you desire large sub cooling

and why?

(b) A simple saturation ammonia compression system has a high pressure of 1.35

MN/m2 and a low pressure of 0.19 MN/m2, Find per 4,00,000 Kj/hr of re- frigerating capacity, the power consumption of compressor and C.O.P. of the cycle. [4+12]