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GUJARAT TECHNOLOGICAL UNIVERSITY
DIPLOMA ENGINEERING – SEMESTER – V • EXAMINATION – WINTER 2016
Subject Code: 3351901 Date: 18- 11- 2016
Subject Name: Thermal Engineering - II
Time: 10:30 AM TO 01:00 PM Total Marks: 70
Instructions:
1. Attempt all questions.
2. Make Suitable assumptions wherever necessary.
3. Figures to the right indicate full marks.
4. English version is authentic.
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Q.1 Answer any seven out of ten. 14
1. Explain the need of supercharging in IC Engine.
2. Define mean effective pressure of an engine.
3. State function of (i) Carburettor (ii) fly wheel
4. What is CNG ? State four advantages of CNG as fuel.
5. Name the parts of IC Engine which require lubrication.
6. Define Net refrigerating effect.
7. State equation of COP for reversed Joule cycle.
8. What is Air-conditioning ? Classify it.
9. What is Bharat Stage ? Explain it.
10. What is psychometry ? Enlist various psychometric process.
Q.2 (a)Classify Internal Combustion engine. 03
OR
(a) Differentiate four stroke and Two stroke engine 03
(b) State the methods of IC engine cooling and describe the water jacket system of cooling with sketch 03
OR
(b) Explain battery coil ignition system of SI engine with sketch. 03
(c)Explain the working of fuel pump with neat sketch. 04
OR
(c)Explain the working of two stroke petrol engine with neat sketch. 04
(d) State different types of scavenging methods and explain cross flow scavenging. 04
OR
(d)Expl ain the working of four stroke diesel engine with sketch. 04
Q.3 (a) Following observations refer to the test of two stroke single cylinder engine
Mean effective pressure : 550 kpa Bore : 21cm
Piston Stroke : 28 cm
Speed : 6 R.P.S.
Braake torque: 628 Nm
Fuel Consumption: 8.16 kg/h
Caloific value of fuel : 42700 kJ/kg
Find Mechanical Efficiency,Indicated Thermal Efficiency,Brake Thermal Efficiency and Brake specific fuel consumption. 07
OR
(a) During trial of four stroke single cylinder engine
Cylinder diameter : 0.3 m
Stroke : 0.5 m
Compression ratio : 6.23
mean effective pressure : 8 bar
Speed : 300 R.P.M.
Fuel consumption :25 m3/h
Calorific value of fuel : 21500 kJ/ m3
Find Indicated power , Indicated thermal efficiency ,Air standard efficiency ( ϒ = 1.4) , relative efficiency. 07
(b) Why need of Alternate fuels is arises ? 03
OR
(b) Describe advantages and disadvantages of Natural gas. 03
(c) Describe working of window air conditioner with neat sketch. 04
OR
(c) The dry bulb and wet bulb temperature of air are 210C and 180C respectively .Barometric pressure of air is 101.325 kPa. Find partial pressure of water vapour if saturation pressure at WBT is 2.0643 kPa. 04
Q.4 (a) Define (i) Dew point temperature (ii) specific humidity (iii) relative humidity 03
OR
(a)Enlist important points for maintenance of Air conditioners. 03
(b) What is psychometric chart? Draw it and show four air properties lines and label it. 04
OR
(b) Define any two (i) Refrigerant(ii) COP (iii) Ton of refrigeration 04
(c) The temperature limit of an ammonia refrigerating system are 250C and -100C if the gas is dry at the end of compressor .calculate Net refrigerating effect and COP assuming no under cooling. Use values from Table.
Q.5 (a) Explain the effect of subcooling of liquid and superheating of vapour on the performance of VCR system. Show the process on p-h diagram. 04
(b) Expl ain the working of a water coo ler with neat sketch. 04
(c)State the desirable characteristics of refrigerant. 03
(d)Differentiate between wet and dry compression. 03
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