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Code :R5220306 R5II B.Tech II Semester (R05) Supplementary Examinations, December 2010

THERMAL ENGINEERING-I(Mechanical Engineering)

Time: 3 hours Max Marks: 80Answer any FIVE questions

All questions carry equal marks

1. (a) Explain the working principle of a fuel injector with suitable diagram?

(b) Discuss the differences between two-stroke engine and four-stroke engine?

2. (a) What is abnormal combustion in S.I. Engine? Compare the abnormal combustion withnormal combustion.

(b) Explain the desirable characteristics of a good combustion chamber for S.I.Engine.

3. (a) What are different four stages of combustion in C.I. Engine? Explain salient features.

(b) How to minimize diesel knock? Explain different controlling methods.4. (a) Derive an expression for the calculation of indicated mean effective pressure.

(b) Define mean effective pressure. A single cylinder 4-stroke CI engine has a bore and strokeof 75mm and 100 mm respectively. Find the bmep if the torque is 25 N-m.

5. (a) Discuss how the clearance affects the performance of multistage compressors.

(b) In two stage compressor, prove that the work done on 1 kg of air is minimum with perfectintercooling when the intermediate pressure is the geometric mean of the suction anddelivery pressure or pi =

pdps .

6. (a) What is pressure coefficient for radial, forward and backward-swept impeller blades. =

12 cot 2 andplot2 curves for radial, forward and backward-swept impeller blades.(b) Prove the following for isentropic flow in a radial-tipped impeller:

= 1; Pro = (1 + u22/CpT01)/1

(c) Determine the pressure ratio developed and the power required to drive centrifugal air Aircompressor (impeller diameter = 45 cm)running at 7200 rpm. Assume zero swirl at theentry and T01 = 288K.

7. (a) What are the advantages of using a flash chamber in parallel with evaporator? Show thatthe use of flash chamber has no effect on the thermodynamics of the cycle and Powerrequired by the system in ideal condition.

(b) A compressor 10 cm

10 cm single acting twin cylinder, 900 r.p.m. is working on F-12with condensing temperature of 380C and evaporator temperature of 40C. Compression isisentropic and vapour is just dry and saturated at the end of compression. Calculate.

i. The capacity of the refrigerator.ii. Power required to run the compressor if the volumetric efficiency of the compressor is

85%.iii. C.O.P. of the system.

8. (a) Define the term effective temperature and explain its significance in the design of air-conditioning systems.

(b) At a certain locality the DBT of air is 300C and the relative humidity is 40%. Determinethe specific humidity and the dew-point and wet bulb temperatures of air. If this air is

cooled in an air washer using recirculated spray water and having a humidifying efficiencyof 0.9, what are the DBT and DPT of air leaving the air washer?

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