Alpha College of Engineering

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1 Alpha College of Engineering Department of Mechanical Engineering TURBO MACHINE (10ME56) QUESTION BANK PART-A UNIT-1 1. Define a turbomahcine. Write a schematic diagram showing principal parts of a turbo machine. (Dec 2012, July 2014, July2015) 2. Compare a turbomahcine and a positive displacement machine. (Dec 2012, July2013) 3. Explain specific speed and specific power. (July 2014) 4. A model turbine 1 m in diameter acting under a head of 2 m runs at 150 rpm. Estimate the scale ratio if the prototype develops 20 MW under a head of 225 m with a specific speed of 100. (July 2014) 5. Define the following efficiencies of power absorbing turbo machines: i. Total-to-total efficiency ii. Static-to-static efficiency (July 2014) 6. Define i) adiabatic efficiency ii) Mechanical efficiency. (Dec 2013) 7. Deducing an expression, explain the significance of second law of thermodynamics applied to a turbo machine. (Dec 2013) 8. A Francis turbine model is built to scale of 1: 5. The data for model is P = 4 KW, N = 3500 rpm, H = 2 m and for prototype, H = 6 m. Assume that the overall efficiency of the model as 70%, calculate i) Speed of the prototype ii) Power of the prototype. (July 2013) 9. The quantity of water available for a hydroelectric power station is 260 m 3 /s under a head of 1.73m. Assuming the speed of the turbine to be 50 rpm and their efficiency to be 82.5%, find the number of turbine required. Assume specific speed 890 rpm. (Jan 2014)

2 10. Define specific speed of a turbine. Obtain an expression for the same in terms of P shaft power, speed and head. (July2013) 11. Two geometrically similar pumps are running at same speed of 1000 rpm. One pump has an impeller diameter of 0.3 m and lifts water at the rate of 20 liters/sec against a head of 15 m. Determine the head and impeller diameter of other pump to deliver half the discharge. (July2013) 12. Explain the significance of first and second law of thermodynamics applied to a trubomachine. (Jan.2015) 13. Define the specific speed of a pump. Obtain an expression for the same in terms of discharge, speed and head. (Jan.2015, July2015) 14. A one-fourth scale turbine model is tested under a head of 10 meters. The prototype is required to work under a head of 30 meters and to run at 425rpm. Estimate the speed of the model if it develops 125 kw and uses 1.1 m3/s of water at this speed. Also calculate the power output of the prototype and suggest the type of turbine. (Jan.2015) UNIT-2 1. Define static and stagnation states. (Dec 2012, Jan.2015) 2. Derive an expression for stage efficiency of a compressor in terms of stage pressure ratio. Indicate the process on T-S diagram. (Dec2012, July2013) 3. Air enters a compressor at a static pressure of 15 bars, static temperature of 15 and flow velocity of 50 m/s. At exit, the static pressure is 30 bars, static temperature of 100 C and flow velocity of 100 m/s. The outlet is 1 m above the inlet. Find a) isentropic change in total enthalpy and b) Actual change in total enthalpy. (Dec2012, July2013) 4. What is reheat factor in a multistage turbine? Prove that R.F is greater than unity (July 2014, Jan.2015, July2015) 5. Define polytrophic efficiency of a compressor (July 2014) 6. In a three stage turbine the pressure ratio of each stage is 2 and the stage efficiency is 75%.Calculate the overall efficiency and reheat factor. (July 2014)

3 7. Give classification of fluid flow based on Mach number and explain in brief. (Jan.2015) UNIT-3 & UNIT-4 1. Derive Euler turbine equation, state the assumptions made. (Dec2012, July2013) 2. Derive an alternate form of Euler's turbine equation and explain the significance of each energy components. (July 2014) 3. At a 50% reaction stage axial flow turbine, the mean Blade diameter is 0.6 meter. The maximum utilization factor is 0.85 and steam flow is 12 kg/s. Calculate the inlet and outlet absolute velocities and power developed if the speed is 2500 rpm. (July 2014) 4. Derive an expression of theoretical head capacity relationship of-radial outward flow devices (centrifugal machines). (July 2014) 5. Draw the velocity triangles for axial flow compressor. From the triangles show that degree of reaction for axial flow compressor is given by,= 2 ( 1 2). Assume axial velocity to remain constant. 1 2 are angles made by relative velocities with the axial direction. (July2013) 6. Draw velocity triangles for the following types of vanes of centrifugal pumps and compressors: i) Backward vane ii) Radial vane iii) Forward Curved Vane. (Jan 2013) 7. For a radial flow turbo machine show that degree of reaction,=2+ 24, where 2= discharge blade angle. (Dec 2012, July2013) 8. Define utilization factor and degree of reaction. Obtain a relation between degree of reaction and the utilization factor. (Dec 2012, Jan.2015, July2015) 9. In an axial flow turbine, the discharge blade angles are 20 each, for both the stator and the rotor. The steam speed at the exit of the fixed blade is 140 m/s. The ratio of Vax/u = 0.7 at the entry and 0.76 at the exit of the rotor blade. Find the inlet rotor blade angle, the power developed by the blade ring for a mass flow rate of 2.6 kg/s. (Dec 2012, July2013) 10. The mean rotor blade speed of an axial flow turbine stage with 50% reaction is 210 m/s. Steam emerges from the nozzle inclined at 28 to the plane of the wheel with axial component equal to blade speed. Assuming symmetric inlet and outlet velocity triangles, determine the rotor blade angle

4 and utilization factor. Also determine the degree of reaction to make the utilization maximum if the axial velocity, blade speed, as well as nozzle angle remain the same. (Jan.2015) 11. The velocity of steam out flow from a nozzle in a Delaval turbine is 1200 m/s. The nozzle angle being 22. If the rotor blades are equiangular and the rotor tangential speed is 400 m/s. Compute: i) Power output assuming Vrl= Vr2. ii) Utilization factor. (July 2013) 12. Show that the alternate form of Euler's turbine equation can be expressed as follows =( 12 22)+( 12 22)+( 12 22)2 (July2013) 13. Draw the velocity diagram for a power absorbing radial flow turbo machine and show that R=12(1+Vm2cotβ2U2). (Jan.2015) 14. Draw the velocity triangles at inlet and outlet of an axial flow compressor from the following data. Degree of reaction 0.5, inlet blade angle 45, axial velocity of flow which is constant throughout 120 m/s, speed of rotation 6500 rpm, radius of rotation 20cm, and blade speed at inlet is equal to blade speed at outlet. Calculate angles at inlet and outlet. Also calculate power needed to handle 1.5 kg/s of air. (Jan.2015) 15. Sketch velocity diagrams for R = 0 and R = 0.5 and label. (Jan.2014) PART-B UNIT-5 1. With sketches explain velocity and pressure compounding. (Dec 2012, July 2014) 2. Define: i) rotor efficiency and ii) stage efficiency of a steam turbine. (Dec 2013) 3. For a 50% reaction steam turbine, show that α1=β2and α2=β1 where α1 and β1 are the inlet angles of fixed and moving blades, α2 and β2 are the outlet angles of fixed and moving blades. (Dec 2012, July2013, Jan.2015) 4. Steam emerging from a nozzle to an impulse De-Laval turbine with a velocity of 1000 m/s. The nozzle angle is 20. The mean blade velocity is 400m/s. The blades are symmetrical (β1=β2). The mass flow rate of steam is 1000 kg/hr. Friction factor is 0.8. Calculate the following: i) Blade angles; ii) Axial thrust; iii) Work done per kg of steam; iv) Power developed. (Jan.2015)

5 5. What is compounding in steam turbine? Explain with neat sketch impulse-reaction turbine. (July2015) 6. In a single stage impulse steam turbine the mean diameter of the blades is 1m. It runs at 3000rpm. The steam is supplied from a nozzle at a velocity of 350m/sec and the nozzle angle is 20. The rotor blades are equiangular. The blade fraction factor is Draw the velocity diagram and calculate the power developed if the axial thrust is N. (July2015) UNIT-6 1. Mention the general characteristic features of Pelton, Francis and Kaplan turbines. (Jan 2013) 2. Explain the function of a draft tube and mention its types. (Dec 2012, Jan.2015) 3. Draw the inlet and exit velocity triangles for a pelton wheel turbine. Show that maximum hydraulic efficiency. (July2013, July 2014, July2015) 4. The internal and external diameters of an inward flow reaction turbine are 1.2 m and 0.6 m respectively. The head on turbine is 22 m and velocity of flow through the runner is constant and is equal to 2.5 m/s. The guide blade angle is 10 and the runner vanes are radial at inlet. If the discharge at outlet is radial. Find i) Speed of turbine ii) Vane angle at outlet iii) Hydraulic efficiency iv) Draw velocity triangles. (July2013) 5. A Pelton wheel is to be designed for a head of 60m when running at 200 rpm. The Pelton wheel develops kw shaft power. The velocity of the buckets = 0.45 times the velocity of the jet, overall efficiency = 0.85 and coefficient of velocity is equal to Find diameter of jet, diameter of wheel, size of buckets and number of buckets. (Dec 2014) 6. The following data are given for a Francis turbine net head = 70 m, speed = 600 rpm, power at the shaft, = kw, overall. Efficiency = 85%, Hydraulic efficiency = 95%, Flow ratio = 0.25, Width ratio = 0.1, outer diameter to inner diameter ratio = 2.0. The thicknesses of vanes occupy 10% of the circumferential area of runner. Velocity of flow is constant at inlet and outlet and discharge is radial at outlet. Determine i) Guide blade angle ii) Runner vane angles iii) Diameter of runner at inlet and outlet iv) Width of wheel at inlet. (Dec 2013)

6 7. A Kaplan turbine has an outer diameter of 8m and inner diameter as 3m and developing 30,000 KW at 80 rpm under a head of 12 m. The discharge through the runner is 300 m3/sec. If the hydraulic efficiency is 95%, determine: i. Inlet and outlet blade angles ii. Mechanical efficiency iii. Overall efficiency (July 2014) 8. Write a short note on draft tubes in a reaction hydraulic turbine. (Jan.2015) 9. In a power station single jet Pelton wheel produces kw under a head of 1770m while running at 750 rpm. Estimate: i) Jet diameter; ii) Mean diameter of the runner; iii) Number of buckets. Assume the necessary data suitably. (Jan.2015) 10. An inward flow reaction turbine works under a head of 110m. The inlet and outlet diameters of the runner are 1.5m and 1.0m respectively. The width of the runner is constant throughout as 150mm. The blade angle at outlet is 15. The hydraulic efficiency is 0.9. Calculate: i) The speed of the turbine. ii) The blade angles. iii) The power produced when the discharge velocity is 6m/s. (Jan.2015) 11. The following data are given for a Francis turbine net head = 60 m, speed = 700 rpm, power at the shaft, = kw, overall. Efficiency = 84%, Hydraulic efficiency = 93%, Flow ratio = 0.20, Width ratio = 0.1, outer diameter to inner diameter ratio = 2.0. The thicknesses of vanes occupy 5% of the circumferential area of runner. Velocity of flow is constant at inlet and outlet and discharge is radial at outlet. Determine i) Guide blade angle ii) Runner vane angles iii) Diameter of runner at inlet and outlet iv) Width of wheel at inlet.

7 UNIT-7 1. Define the following for a centrifugal pump: i) Static head ii) Suction head iii) Delivery head iv) Manometric head (with the help of a schematic diagram). (Dec 2012, July2013) 2. What are the applications of multi-stage centrifugal pumps? With a neat sketch, explain centrifugal pumps in series and parallel. (Dec 2012, July2013) 3. What is priming? How priming will be done in centrifugal pump? (Dec 2012, July 2014) 4. A centrifugal pump with an impeller outer diameter of 1.05 m runs at 1000 rpm. The blades are backward curved and they make an angle of 20 with the wheel tangent at the blade tip If the radial velocity of flow at the tip is 8 m/sand the slip coefficient is 0.86, find: i) The actual work-input/kg of water flow ii) The absolute velocity of fluid at the impeller tip iii) The hydraulic efficiency, considering the kinetic energy at the outlet as wasted. If the pump is fitted with a diffusion chamber with an efficiency of 0.75 so that the exit velocity is reduced to 5 m/s, find the new hydraulic efficiency. (Dec 2012, July2015) 5. Explain the Cavitations in pumps. (July2013) 6. Outer diameter of a pump is 50 cm and inner diameter is25 cm and runs at 1000 rpm, against a head of 40 m. velocity of flow is constant and is equal to 2.5 m/s. Vanes are set back at an angle of 40 at the outlet. Width at outlet is 5 cm. Find, i) Vane angle at inlet ii) Work done by impeller iii) Manometric efficiency. (July2013)

8 7. Derive the expression for the minimum speed for starting a centrifugal pump. (July 2014, Jan.2015, July2015) 8. A centrifugal pump having outer diameter equal to two times the impeller diameter and running at 1200 rpm, works against a total head of 75 m. The velocity of flow through the impeller is constant and equal to 3m/sec. The vanes are setback at an angle of'30 at outlet. If the outlet diameter of the impeller is 60 cm and width at outlet is 5 cm determine: i. Vane angle at inlet ii. Work done per second by impeller iii. Manometric efficiency (July 2014) 9. A centrifugal pump is to discharge m3/s of water at a speed of 1450rpm against a head of 25m. The impeller diameter is 25cm and its width at the outlet is 5cm and Manometric efficiency is 75%. Calculate the vane angle at the outlet. (Jan.2015) 10. A centrifugal pump with 1.2m diameter runs at 200rpm and pumps 1.88m3/s, the average lift being 6m. The angle which the vane makes at exit with the tangent to the impeller is 26 and the radial velocity of flow is 2.5 m/s. Find the Manometric efficiency and the least speed to start pumping if the inner diameter being 0.6m. (Jan.2015) 11. The outer diameter of the impeller of a centrifugal pump is 40cm, and width of the impeller at outlet is 5cm. the pump is running at 800rpm and is working against a total head of 15m. The vane angle at outlet is 40 and Manometric efficiency is 75%. Determine: i) Velocity of flow at outlet, ii) velocity of water leaving the vane iii) angle made by the absolute velocity at outlet with the direction of motion at outlet iv) Discharge (July 2015)

9 UNIT-8 1. Define the following terms of centrifugal compressor: i) overall pressure ratio ii) pressure coefficient iii) slip factor iv) Power factor. (Dec 2012, July2013) 2. Explain the phenomenon of surging in centrifugal compressor. (Dec 2012, July 2014) 3. Discuss the following for a centrifugal compressor: i) Compressibility and pre whirl. ii) Diffuser design. (Dec 2014) 4. With the help of H -Q plot explain the phenomena of surging in centrifugal compressors. (July2013) 5. Draw velocity triangles at the entry and exit for the axial compressor stage. (July 2014) 6. With neat sketch explain, slip, slip coefficient and slip factor. (Jan.2015) 7. Explain the phenomenon of surging and stalling. (Jan.2015) 8. The mean diameter of the rotor of an axial flow compressor is 0.5m and it rotates at rpm. The velocity of flow 220 m/s is constant and the velocity of whirl at the inlet is 80m/s. The inlet pressure and temperature are 1 bar and 300 K. The stage efficiency is The pressure ratio through the stage is 1.5. Calculate i) Fluid deflection angle ii) the degree of reaction if work done factor is 0.8. (Jan.2015) 9. Briefly explain the following: i. Surging of compressors. ii. Slip factor or slip coefficient. (July.2015)