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GUJARAT TECHNOLOGICAL UNIVERSITY
DIPLOMA ENGINEERING – SEMESTER – • EXAMINATION – Summer 2015
Subject Code:3351901 Date: 01/05 /2015
Subject Name: THERMAL ENGINEERING-II
Time: 2:30 pm to 5:00 pm Total Marks: 70
Instructions:
1. Attempt all questions.
2. Make Suitable assumptions wherever necessary.
3. Figures to the right indicate full marks.
4. Use of programmable & Communication aids are strictly prohibited.
5. Use of only simple calculator is permitted in Mathematics.
6. English version is authentic.
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Q.1 Answer any seven out of ten. 14
1. Classify I C Engine.
2. List reasons for failing a spark plug.
3. Write advantages of Air-cooled engine.
4. List various types of alternative fuels.
5. Define C O P of refrigeration.
6. Explain working of capillary tube.
7. Mention chemical name and chemical formula of refrigerant R-12 and R-22
8. Define Air-conditioning
9. Explain Dew point temperature on T-S diagram.
10. Explain working of condenser.
Q.2 (a) Define following terms used for I C Engine:
(i) Top Dead Centre (ii) Clearance Volume (iii) Compression Ratio 03
OR
(a) Derive the equation for Brake Power from rope brake dynamometer. 03
(b) Explain the reason for the need of alternative fuels. 03
OR
(b) Explain Biodiesel as an alternative fuel. 03
(c) Differentiate between two stroke engine and four stroke engine. 04
OR
(c) Differentiate between S I Engine and C I Engine. 04
(d) The following data was recorded during a test run made on a single cylinder, four stroke engines having a compression ratio of 6.
(i) Bore and stroke = 10 cm and 12.5 cm respectively
(ii) Dead load and spring balance reading = 60 N and 20 N
(iii) Effective radius of brake drum = 40 cm
(iv) Fuel consumption = 1.2 kg/hr
(v) Calorific value of fuel = 42500 kJ/kg,
If the engine turns 2000 rpm and the indicated mean effective pressure is 0.25 MPa, determine its Indicated Power (I P), Brake Power (B P), Mechanical Efficiency (ηm) and Overall Efficiency (ηo). 04
OR
(d) In a diesel engine fuel consumption is 6.5 kg/hr. If engine brake power is 22.4 kW and mechanical efficiency is 75%, calculate the following; (Take CV=21500kJ/kg) 04
(i) Indicated Power
(ii) Indicated Thermal Efficiency
(ii) Brake Thermal Efficiency
(iv) Specific Fuel Consumption for B P
Q.3 (a) “Theoretical valve timing diagram and actual valve timing diagram are different.” Explain with reason. 03
OR
(a) List the advantages of MPFI system. 03
(b) Define (i) Flash Point (ii) Fire Point (iii) Pour Point 03
OR
(b) List the advantages of CNG as an alternative fuel. 03
(c) Explain the vapor compression cycle on P-V, T-S, and P-h diagram with its 04
OR
(c) Compare Hermetically sealed compressor with open compressor. 04
(d) Define following terms;
(i) Dry bulb temperature
(ii) Wet bulb temperature
(ii) Humidity ratio
(iv) Relative humidity 04
OR
(d) Show the following processes on psychometric chart and explain;
(i) Heating with Humidification
(ii) Cooling with Dehumidification 04
Q.4 (a) Explain splash lubrication system for IC Engines. 03
OR
(a) List safety precautions in IC Engine. 03
(b) Explain Dry Expansion (DX) evaporator in detail. 04
OR
(b) Explain Automatic Expansion valve in detail. 04
(c) The temperature limits of an Ammonia refrigerating system are 25°C and −10°C. If the gas is dry at the end of compression and there is no under cooling of the liquid Ammonia. Plot the system on T-S and P-h diagram, and calculate the COP of the cycle. Use the following table for properties of ammonia 07
Q.5 (a) Explain split Air-conditioning system with neat sketch. 04
(b) State advantages, limitations and applications of vane type axial fan. 04
(c) State purpose of governing and write brief note on quality governing. 03
(d) List the factors affecting the location of cold storage. 03
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