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Posted By: CONFIDENCE IS THE COMPANION OF SUCCESS Member Level: Diamond Posted Date: 23 Apr 2008
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2007 Anna University B.E Mechanical Thermal Engineering Question paper
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Part- A (10*2=20 marks)
1. Sketch the Diesel cycle on P-Vand T-S planes .
2. List out any two assumptions for the analysis of thermodynamic air cycles .
3. what is the function of camshaft and crankshaft.
4. List out the effects of detonation.
5. Define nozzle efficiency.
6. Give the working principle of an impulse turbine.
7. Define the volumetric efficiency of air compressor.
8. What is free air delivered.
9. A carnot refrigerator requires 1.3 kW per tonne of refrigerationto maintain a region at low temperature of -380 C. Determine the COP of the refrigerator
and the higher temperature of the cycle.
10. Define dew point temperature.
PART-B (5*16=80 marks)
11. (a) An engine working on otto cycle has a volume of 0.45 m3,pressure 1 bar
and temperature 300C at the beginning of compression stroke.At the end
of compression stroke, the pressure is 11 bar and 210 kj of heat is added
at constant volume.determine
(i) pressures,temperatures and volumes at salient points in the cycle
(ii) efficiency
(or)
(b) (i) Derive an expression for the air-standard efficiency of a brayton
cycle in terms of pressure ratio.
(ii) Prove that the pressure ratio for maximum work is a function of the
limiting temperature ratio.
12. (a) (i) Explain any four types of classification of internal Combustion
engines.
(ii) With a neat sketch explain any one type of ignition system.
(or)
(b)Following data relates to 4 cylinder,A stroke petrol engine.Air/Fuel ratio
by weight 16:1.Calorific value of the fuel = 45200 kj/kg, mechanical
efficiency = 82%. Air standard efficiency = 52%,relative efficiency = 70%
volumetric efficiency = 78%,stroke/bone ratio = 1.25 suction conditions =
1 bar,250C.Speed=2400rpm power at brakes = 72KW.Calculate
(i) Compression ratio
(ii) Indicated thermal efficiency
(iii) Brake specific fuel consumption and
(iv) Bore and stroke.
13. (a) (i) Derive an expression for the critical pressure ratio in terms of the
index of expansion.
(ii) Dry saturated steam enters a steam nozzle at a pressure of 15 bar
and is discharged at a pressure of 2.00bar.If the dryness fraction of
discharge steam is 0.96, what will be the fi9nal velocity of steam.
Neglect initial velocity of steam,If 10% of heat drop is lost in
Friction, find the percentage reduction in the final velocity.
(or)
(b) A 50% reaction turbine funning at 400 rpm has the exit angle of the blades
as 200 and the velocity of the steam relative to the blades at the exit is
1.35times the mean speed of the blade. The steam flow rate is 8.33 kg/s and
at particular stage the specific volume is1.381 m3/kg. calculate for this stage.
(i) a suitable blade height , assuming the rotor mean diameter 12 times the
blade height , and
(ii) the digram work.
14 (a) (i) Derive an expression for maximum work required for a two stage
reciprocating air compressor with perfect inter cooling and neglecting
clearance.
(ii) A two stage air compressor compresses air from 1bar and 200C to 42
bar . if the law of compression is pv1.35 = constant and the inter cooling
is perfect. Find per kg of air
(1) the work done in compression
(2) the mass of cooling water necessary for abstracting the heat in the inter
cooler, if the temperature rise of the cooling water is 250C.
(or)
(b) (i) With a neat sketch describe any one type of rotary compressor.
(ii) A single stage single acting reciprocating air compressor deliovers 14 m3 of
free air per minute from 1bar to7bar. The speed of the compressor is 310
rpm .Assuming that compression and expansion follws the law pv1.35=
and clearance is 5% of the swept volume, find the diameter and stroke of
thecompressor . take stroke length is 1.5 times the bore dia.
15. (a) A refrigeration system of 10.5 tonnes capacity at an evaporator temperature of
-120C and an condenser temperature of 270C is needed in food storage locker .
the refrigerant ammonia is sub cooled by 60C before entering the expansion
valve. The vapour is 0.95 dry as it leaves the evaporator coil. The compression
in the compressor is of adiabatic type . Find
(i) Condition of vapour at the outlet of the compressor
(ii) Condition of the vapour at the entrance of the evaporator
(iii) COP
(iv) The power required.
Neglect valce throttling and clearance effect.
(or)
(b) A sling psychrometer in alaboratory test recorded the following readings
Dry bulb temperature = 350 C
Wet bulb temperature = 250 C
Calculate the following :
(i) specific humidity
(ii) relative humidity
(iii) vapourdensity in air
(iv) dew point temperature
(v) enthalpy of mixture per kg of dry air
Take atmospheric pressure = 1.0132 bar.
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