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Gas Turbine & Jet Propulsion (October 2009)

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Total No. of Questions : 12] [Total No. of Pages : 4 [3664] - 125 P970 B.E. (Mechanical) GAS TURBINE & JET PROPULSION (2003 Course) (402044) Time : 3 Hours] [Max. Marks : 100 Instructions to the candidates: 1) Answer three questions from Section I and three questions from Section II. 2) Answers to the two sections should be written in separate books. 3) Neat diagrams must be drawn wherever necessary. 4) Figures to the right indicate full marks. 5) Use of logarithmic tables, slide rule, Mollier charts, electronic pocket calculator and steam tables is allowed. 6) Assume suitable data, if necessary. SECTION - I UNIT - I Q1) a) What do you understand by the term stagnation state? Give its practical importance. Hence define stagnation enthalpy, pressure & temp. Prove that stagnation temp., T 0 = T + b) C2 . 2.C p [8] Air enters diffuser at velocity of 150 m/sec at static condition of 1 bar & 15oC. The diffuser efficiency is 95%. Determine the exit stagnation conditions. Assume Cp = 1.005 kJ/kg K. A = 1.4 & R = 287 Nm/kg K. [8] OR Q2) a) b) c) Explain the following terms related to nozzles [4] i) Velocity coefficient. ii) Dischange coefficient. What do the states on fanno line & Rayleigh line represent? What do the intersection points of these two curves represent? [4] A convergent nozzle is to discharge 1 kg/s of gas. The gas enters a nozzle at stagnation conditions of 5 bar & 727oC & it leaves at speed of 500 m/sec. Assuming the flow to be isentropic, determine the pressure & nozzle area at the exit. [8] UNIT - II Q3) a) Give comparison between centrifugal compressor & axial flow compressor. [5] P.T.O. b) c) Explain the phenomenon of surging. [5] A rotary air compressor working between 1 bar & 2.5 bar has internal & external diameters of impeller as 300 mm & 600 mm respectively. The vane angle at inlet & outlet are 30o & 45o respectively. If air enters impeller at 15 m/s. Find i) ii) Speed of impeller in r.p.m. Work done by compressor per kg of air. [8] OR Q4) a) b) Explain - Degree of reaction. [5] Explain the phenomenon of stalling of blades in axial flow compressor. [5] c) An axial flow compressor having eight stages & with 50% reaction compresses air in pressure ratio of 4 : 1. The air enters compressor at 293 K & flows through it with constant speed of 90 m/sec. The rotating blades of compressor rotate with mean speed of 180 m/sec. Isentropic efficiency of compressor may be taken as 0.82. Calculate i) Work done by the machine. ii) Blade angles. [8] UNIT - III Q5) a) How gas turbines are classified? Prove that thermal efficiency of gas turbine is given by th = 1 b) 1 () rp n 1 . [6] A gas turbine set draws in atmospheric air at 1.013 bar & 15.6 C; there are two pressure stages with intercooler & the total pressure ratio is 8 : 1. The maximum temperature of the cycle is 593 C & there is one turbine for expansion. A regenerator is used & recovers 80% of available heat. Determine efficiency of the plant & work ratio. The turbine & compressor efficiencies may be taken as 0.86 & 0.83 respectively. [10] OR Q6) a) b) What are advantages and disadvantages of gas turbines over I.C. engine? [6] A gas turbine plant consists of one turbine for compressor drive & another for output & both are having their oven combustion chambers which are served by air divertly from compressor. Air enters compressor at 1 bar & 15oC & is compressed with isentropic efficiency of 0.76. Gas inlet temperature & pressure in both turbine are 680oC & 5 bar. The isentropic [3664] - 125 -2- efficiency of turbine is 0.86. The mass flow rate of air at compressor inlet is 23 kg/sec. The C.V. of fuel is 42000 kJ/kg. Calculate the output of plant & thermal efficiency assuming Cp = 1.005 & r = 1.4 for air. Cp = 1.128 & r = 1.34 for gas. [10] SECTION - II UNIT - IV Q7) a) b) Explain the working of a single impulse stage of a Gas Turbine. Draw the velocity s . Derive expression for maximum utilization factor. What is velocity compounding and pressure compounding? Explain with a diagram. [10] Discuss the performance graphs of a Gas Turbine. [6] OR Q8) a) b) Explain the working of general reaction stage of a Gas Turbine with the help of schematic and enthalpy - entropy diagrams. Show the isentropic expansion and actual expansion. Define degree of reaction and show a 50% reaction stage on enthalpy - entropy diagram. [8] The following data refers to a single stage impulse gas turbine. [8] o i) Nozzles are inclined at 20 to the plane of rotation and discharge the gas at 750 m/s. ii) Mass flow rate of gas = 100 kg/s. iii) RPM = 20000. iv) Mean diameter of the wheel = 31.5 cm. v) Blade velocity coefficient = 0.92. vi) Outlet blade angle = 25o. Calculate 1) Power developed by the turbine. 2) Utilization factor. UNIT - V Q9) a) b) c) Discuss the combustion theory applied to gas turbine combustor. [6] Explain the combustion intensity and combustion efficiency. List the [6] factors affections the combustion chamber design. Discuss the working of a typical gas - turbine combustion chamber with a neat sketch. [6] OR [3664] - 125 -3- Q10)Write notes on : [18] a) Fuels for gas turbines and pollution problems. b) Fuel injection and ignition systems for Gas Turbines. c) Materials for Gas Turbine components. UNIT - VI Q11)a) Discuss the basic theory of Rocket propulsion. Derive expressions for thrust, thrust power and propulsive efficiency. [8] b) Determine the thrust of a rocket motor in which the propellant flow rate = 10 kg/S. The exit area of nozzle is 400 cm2 and absolute exhaust velocity = 2000 m/s : Ambient pressure = 1 bar. [4] c) List the applications of rockets. [4] OR Q12)Explain the working of the following with a neat sketches : a) Turbofan engine. b) Pulse - jet engine. c) Nuclear Rocket engines. d) Magneto plasma rocket engines. [3664] - 125 -4- [16]

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