Thermal & Fluid Power Enngineering - May 2015
Mechanical Engineering (Semester 6)
TOTAL MARKS: 80
TOTAL TIME: 3 HOURS (1) Question 1 is compulsory.
(2) Attempt any three from the remaining questions.
(3) Assume data if required.
(4) Figures to the right indicate full marks.
Write short note on (any four):
1 (a) What is meant by Jet Propulsion? Explain. (5 marks)
1 (b) Write a short note on: Classification of water turbine. (5 marks)
1 (c) Explain briefly the governing system of a Kaplan turbine. (5 marks)
1 (d) Differentiate water tube boilers with fire tube boilers. (5 marks)
1 (e) With neat sketch explain the working of closed cycle gas turbine plant. (5 marks)
2 (a) Explain the working of a Once through boiler with the help of a neat sketch. (8 marks)
2 (b) A 4500 kW gas turbine generating set operates with two compressor stages; the overall pressure ratio is 9:1. A high pressure turbine is used to drive the compressors, and a low pressure turbine drives the generator. The temperature of the gases at entry to the high pressure turbine is 625°C and the gases are reheated to 625°C after expansion in the first turbine. The exhaust gases leaving the low pressure turbine are passed through a heat exchanger to heat air leaving the high pressure stage compressor. The compressor have equal pressure ratios and inter-cooling is complete between the stages. The air inlet temperature to the unit is 20°C. The isentropic efficiency of each compressor stage is 0.8 and the isentropic efficiency of each turbine stage is 0.85, the heat exchanger thermal ratio is 0.8. A mechanical efficiency of 95% can be assumed for both the power shaft and compressor turbine shaft. Neglecting al pressure losses and changes in kinetic energy calculate:
i) the thermal efficiency
ii) work ratio of the plant
iii) the mass flow in kg/s.
Neglect the mass of the fuel and assume the following Cp=1.005 kJ/kg K, and y=1.4. (12 marks)
3 (a) Derive the expression for the condition for maximum blade efficiency in Parson's reaction turbine. (10 marks)
3 (b) A boiler generates 7.5 kg of stream per kg of coal brunt at a pressure of 11 bar, from feed water having a temperature of 70°C. The efficiency of the boiler is 75% and factor of evaporation is 1.15, specific heat of steam at constant pressure is 2.3 kJ/kg K. Calculate:
i) Degree of superheat and temperature of steam generated:
ii) Calorific value of coal is kJ/kg
ii) Equivalent evaporation in kg of steam per kg of coal. (10 marks)
4 (a) Obtain the expression for the force exerted by a jet of water on a fixed curved plate when jet strikes at the center of a symmetrical curved plate. (4 marks)
4 (b) Explain the function of following in Reaction water turbine:
i) Guide vane
ii) Scroll casing
iii) Draft tube (6 marks)
4 (c) A single stage steam turbine is supplied with steam at 5 bar, 200°C at the rate of 50 kg/min. It expands into a condenser at a pressure of 0.2 bar. The blade speed is 400 m/s. The nozzles are inclined at an angle of 207deg; to the plane of the wheel and the outlet blade angle is 30°. Neglecting friction losses, determine power developed, blade efficiency and stage efficiency. (10 marks)
5 (a) Discuss and explain: Method to improve efficiency of a gas turbine. (6 marks)
5 (b) The three jet Pelton turbine is required to generate 10,000 kW under a neat head of 400m. The blade angle at outlet is 15° and the reduction in the relative while passing over the blade is 5%. If the overall efficiency of the wheel is 80%, Cv=0.98 and speed ratio =0.46, then find: (i) the diameter of the jet, (ii) total flow in m3/s and (iii) the force exerted by a jet on the buckets. (10 marks)
5 (c) What are the effects of friction in a nozzle? Define nozzle efficiency, coefficient of velocity. (4 marks)
6 (a) Explain the working of a turboprop engine by means of a sketch. What are its advantages, limitations and applications? (10 marks)
6 (b) In a hydroelectric generating plant, there are four similar turbines of total output 220 MW. Each turbine is 90% efficient and runs at 100 rpm under a head of 65 m. It is proposed to test the model of the above turbine in a flume where a discharge is 0.4 m3/s under a head of 4m. Determine the size (scale ratio) of the model. Also calculate the model speed and power results expected from the model. (6 marks)
6 (c) Write a short note on boiler mountings. (4 marks)