# JNTU PAPERS,B-Tech,I- Semester,Thermal Science, November 2008

JNTU PAPERS

JNTU,B.Tech,I- Semester, Thermal Science, November 2008

( Mechatronics and Production Engineering)

SET-3

1. (a) Explain mechanical, chemical and thermal equilibriums with suitable examples

(b) A piston and cylinder machine containing a fluid system has a stirring device

in the cylinder. The piston is frictionless and it is held down against the

fluid due to the atmospheric pressure of 101.325 KPa. The stirring device is

turned 10,000 revolutions with an average torque against the fluid of 1.275

N-m. Mean while the piston of 0.6 m diameter moves out 0.8m. Find the net

work transfer for the system.

2. A gas undergoes a thermodynamic cycle consisting of three processes beginning at

an initial state where P1=1 bar, V1 = 1.5m3 and U1 = 512 kJ. The processes are as

follows: (i) Process 1-2: Compression with PV=constant to P2 = 2 bar, U2 = 690

KJ (ii) Process 2-3: W2?3=0, Q2?3=- 150 KJ, and (iii) Process 3-1 : W3?1= 50

KJ. Neglecting KE and PE changes, determine the heat interaction Q12 and Q31.

3. (a) State and explain

i. Kelvin – Planck Statement of IInd Law of thermodynamics

ii. Clausius statement of IInd Law of thermodynamics

(b) An engine is to be designed to produce 0.735KW by taking continuously

6000kJ/h from heat source which is at 505K. The heat sink is atmosphere i.e., sink temperature is atmospheric. Calculate the efficiency of car not cycle. The atmospheric temperature varies from 380C in summer and 00c in winter. Comment on the performance of the engine

4. (a) For the same compression ratio and heat rejection, which cycle is most efficient.

Otto, Diesel or dual? Explain with P-V and T-S Diagrams.

(b) An engine working on Otto Cycle in which the salient points are 1,2,3 and

4 has upper and lower temperature limits T3 and T1. If the maximum work per kg of air in is to be done, then show that the intermediate temperature is

given by

T2 = T4 = ?pT1T3

5. In an open system refrigerating machine working on Bell-coleman cycle, 1200 kg

of air is circulated per hour. The suction and compression pressures are 1 bar and

4.5 bar abs. Temperatures before compression and after expansion are 50 C and

-750C.assuming compression expansion to be adiabatic. Calculate

(a) Heat extracted from the cold chamber per hour.

(b) Heat rejected to the cooler and

(c) C.O.P. of the system Take Cp = 1.005 kJ / kg K; ? = 1.4

6. (a) Discuss the need for lubrication in I.C. engines and explain types of lubrication

systems used in I.C.engines.

(b) Name the various fuels used in I.C. engines and the type of ignition with each

one of them.

7. (a) Explain different stages of combustion in S.I.Engine along with p-? diagram.

(b) What is diesel knock? How to minimize knocking in C.I. Engine.

8. (a) What is inter cooling of gas turbine unit? How to enhance the performance

of the gas turbine plant.

(b) The pressure ratio of an open cycle unit is 5 with the temperature range of 300

K and 1050 K. Determine the thermal efficiency and work ratio if isentropic

efficiencies of compressor and turbine are 0.85.