Applied Thermodynamics - Jun 2013

Mechanical Engg. (Semester 4)

TOTAL MARKS: 100
TOTAL TIME: 3 HOURS (1) Question 1 is compulsory.
(2) Attempt any four from the remaining questions.
(3) Assume data wherever required.
(4) Figures to the right indicate full marks. 1 (a) Explain the following:
i) Enthalpy of formation
ii) Combustion efficiency
iii) Enthalpy of combustion
iv) Complete combustion
v) Incomplete combustion(10 marks) 1 (b) The products of combustion of hydrocarbon fuel of unknown composition have the following composition on dry basic:
CO₂=8.0%, CO=0.9%, O₂=8.8%, N₂=82.3%
Calculate:
i) Air-fuel ratio
ii) Composition of fuel on mass basis
iii) The percentage of theoretical air on mass basis.(10 marks) 2 (a) Derive an expression of air standard efficiency of a dual cycle, starting the assumptions made.(10 marks) 2 (b) A diesel engine operation on an air standard diesel cycle has 20 mm bore and 30 mm stroke. The clearance volume is 4.2×10^-4 m³. The fuel is injected for constant pressure for 5% of the stroke, calculate the air standard efficiency. If the cut-off is delayed from 5% to 8% what will be the effect on efficiency?(10 marks) 3 (a) Explain the following:
i) Motoring test method
ii) Willian's line method(8 marks) 3 (b) A two stroke diesel engine was motored when meter reading was 1.5 kW. Test on engine was carried for one hour and data observed were as follows: Brake torque=120 N-m.
C_p(gas)=1.05 kj/kg-k Speed=600 RPM Room temperature=27°C Fuel used=2.5 kg, A:F ratio=32:1 Calorific value=40.3 Mj/kg, Cooling water=818 kg, Rise in temperature of cooling water=10°C.
Exhaust gas temperature 347°C.
Determine brake power, indicated power, brake thermal efficiency. And draw the heat balance sheet on minute basis.(12 marks) 4 (a) Sketch the flow diagram and corresponding T-S diagram of a reheat vapour cycle and derive an expression for the reheat cycle efficiency. What are the advantages gained by reheating the steam in between stages?(10 marks) 4 (b) A steam power station uses the following cycle steam boiler outlet: 150 bar, 550°C Reheat at 0.1 bar, using the Molier diagram and assuming the ideal process find,
i) Quality of steam at turbine exhaust.
ii) Cycle efficiency.(10 marks) 5 (a) Derive an expression for minimum work I/P by two stage compressor with intercooler.(10 marks) 5 (b) The following data refer to a single stage double acting air compressor in which air is drawn at 1 bar and compressor in which air is drawn at 1 bar and compressed to 16 bar, according to the law PV^1.25=C. Input to compressor is 50 kW. The speed of the compressor is 300 RPM. The piston speed is 180 m/min. The volumetric efficiency is 80%. Calculate the diameter and stroke of the cylinder.(10 marks) 6 (a) With neat sketches, explain turbojet and ramjet propulsions.(10 marks) 6 (b) A gas turbine receives air at 100 kPa and 300 K and compresses it to 620 kPa. With compressor efficiency of 88%. The fuel has a heating value of 44180 kJ/kg and fuel air ratio is 0.017 kg of fuel per kg of air. The turbine efficiency is 90%. Calculate the compressor work, turbine work and thermal efficiency.(10 marks) 7 (a) Explain the effect of super heating and sub-cooling with the aid of T-S and P-H diagram.(6 marks) 7 (b) Explain steam jet refrigeration.(4 marks) 7 (c) A vapour compression refrigeration uses Freon-12 has its temperature -10°C and 30°C. The vapour enters the compressor dry and under cooled by 5°C in the condenser. For the capacity of 15 TO R, find
i) COP
ii) Mass of Freon
iii) Power required C_p (vapour)=0.56 kJ/kg-K and C^p (liquid)=1.003 kJ/kg-K(10 marks) 8 (a) Define the following:
i) Wet bulb temperature
ii) Dew point temperature
iii) Relative humidity
iv) Specific humidity
v) Degree of saturation(10 marks) 8 (b) A sling thermometer reads 40°C DBT and 28°C WBT. Find the following:
i) Specific humidity
ii) Relative humidity
iii) Dew point temperature
iv) Vapour density(10 marks)