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GUJARAT TECHNOLOGICAL UNIVERSITY
Diploma Engineering - SEMESTER–V • Examination – WINTER • 2014
Subject Code: 3351901 Date: 26-11-2014
Subject Name: Thermal Engineering - II
Time: 10:30 am - 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 considered to be Authentic.
5. Use following table for Q.3 – b
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Q.1 Answer any seven out of ten. 14
1. Write equation for thermal efficiency in terms of compression ratio with usual notations for CI and SI engine.
2. Define Mean Effective Pressure (MEP) with mathematical equitation.
3. Give any two SI unit for Mean Effective Pressure with inter relation.
4. Draw PV and TS diagramme with name of process (Mechanical and Thermodynamics) for CI engine.
5. Draw PV and TS diagramme with name of process (Mechanical and Thermodynamics) for SI engine.
6. Define Refrigerant.
7. Define Ton of refrigeration. Write down relation between TR and KW from definition.
8. Name any Two hello carbon refrigerant with its chemical formula.
9. State equation of COP for reversed Carnot cycle with usual notations.
10. Name any four expansion device used in VCRS.
Q.2 (a) Draw theoretical and actual valve timing diagramme for four stroke diesel engine. 03
OR
(a) Draw theoretical and actual valve timing diagramme for four stroke petrol engine. 03
(b) Explain reasons for difference in actual and theoretical valve timing diagramme for petrol engine. 03
OR
(b) Explain reasons for difference in actual and theoretical valve timing diagramme for diesel engine. 03
(c) List advantage and disadvantage of Liquid Hydrogen as a fuel. 04
OR
(c) List advantage and disadvantage of LPG as a fuel. 04
(d) Draw sketch for CNG supply system at gas station. 04
OR
(d) List and explain various types of Alternative Fuels. 04
Q.3 (a) A CI engine having break power is 25000 Watt, consume fuel 7.0 Kg/hr. Find Indicated Thermal Efficiency, Break Thermal Efficiency, Break Power and Specific Fuel Consumption based Break Power. The calorific value of fuel is 22000 KJ/Kg. 07
OR
(a) Following observations are available during trial of four stroke single cylinder SI engine.
Diameter of Cylinder: 300mm
Stroke: 500mm
Pressure Ratio: 6
Mean Effective Pressure: 8 bar
Speed: 320 rpm
Calorific Value of fuel: 21000 KJ/M3
Fuel consumption rate: 0.5 M3/min.
Mechanical Efficiency: 70%
Find (1) Indicated Power (2) Break Power (3) Indicated Thermal Efficiency
(4) Cycle Efficiency (5) Specific Fuel Consumption based Break Power. 07
(b) An ammonia refrigeration system (based on VCRS) working between
temperature limits of -10oC and 30o ( 'o' = degree )
C. The vapour is 95% dry at the end of compression and there is no sub cooling of refrigerant. Using table in instruction, find Compressor work, Heat rejected by condenser, Refrigerating effect and COP per Kg of refrigerant. 07
OR
(b) In a 15 TR Ammonia refrigeration plant, the condensing temperature is 30oC and evaporating temperature is -10o ( 'o' = degree )
C. The refrigerant leaving evaporator is dry and saturated and there is no sub cooling take place in condenser. Find out COP and power required to drive the system. Use table given in instruction. Take Cp for Ammonia vapor as 2.8 KJ/KgoK. 07
Q.4 (a) Draw schematic diagramme of VCRS with name of each component. 03
OR
(a) Explain Reverse Brayton Cycle with PV and TS diagramme. 03
(b) Draw T-S and P-h chart for standard VCRS with name of thermodynamic and mechanical process. 04
OR
(b) For Reverse Brayton cycle, derive equation for cycle COP with usual notations. 04
(c) Draw Vapour Absorption Refrigeration System. Explain it with working and advantage. 07
Q.5 (a) Draw Psychometric chart. Indicate all properties on it clearly. 04
(b) Write down Carriers equation for partial pressure of water vapour in moist air with name and unit of notation used in equation. 04
(c) Define (1) Humidity Ratio (2) Absolute Humidity (3) Relative Humidity 03
(d) Draw Window Air Conditioner with name of all components. 03
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