Code No: R Set No. 1

Transcription

1 Code No: R Set No. 1 III B.Tech I Semester Regular Examinations, November 2008 HYDRAULIC MACHINERY AND SYSTEMS ( Common to Mechanical Engineering and Automobile Engineering) Time: 3 hours Max Marks: 80 Answer any FIVE Questions All Questions carry equal marks 1. 5 cm diameter jet having a velocity of 20m/sec, strikes a flat plate, the normal of which is inclined at 25 0 to the axis of the jet. Calculate the normal force exerted on the plate (a) When the plate is stationary (b) When the plate is moving with a velocity of 10m/sec in the direction of the jet. (c) When the plate is moving with a velocity of 7m/sec parallel to itself and in the direction of the normal to its surface. [4+6+6] 2. An outward flow reaction turbine has inner and outer diameter of the wheel as 1000mm and 2000 mm respectively. The water enters the vane at an angle of 20 0 and leaves the vane radially. If the velocity of flow remains constant at 10m/sec and the speed of the wheel is 300rpm, find the vane angles at inlet and outlet. [16] 3. Define the terms unit head, suction specific speed, unit power, unit speed and unit discharge with reference to a hydraulic turbine. Also derive expressions for these terms. [16] 4. (a) Why is the speed of a reciprocating pump lower than that of a centrifugal pump? On what factors does the speed of the reciprocating pump depend? (b) Explain how the separation of flow is caused in reciprocating pumps. What preventive measures are usually taken to reduce the same appreciably? [8+8] 5. (a) How will you obtain an expression for the minimum speed for starting a centrifugal pump? (b) The diameter of an impeller of a centrifugal pump at inlet and outlet are 300 mm and 600 mm respectively. The velocity of flow at outlet is 2.5 m/s and vanes are set back at an angle of 45 o at outlet. Determine the minimum starting speed of the pump if the manometric efficiency is 75 %. [6+10] 6. (a) Explain the following terms as they are applied to a centrifugal pump: i. Static suction lift ii. static suction head iii. static discharge head and iv. total static head. (b) With a neat sketch, explain the principle and working of a centrifugal pump. [10+6] 1 of 2

2 Code No: R Set No Water at a pressure of 50 bar from a accumulator is supplied to a crane which is lifting a weight of 10 kn through a height of 10 m, when the weight is moving up with a speed of 0.3 m/s, once in every two minutes. The water is supplied to the accumulator by a pump. Assuming the efficiency of the crane = 70%, Find (a) The capacity of jigger cylinder, (b) The capacity of the accumulator, and (c) Minimum power required to run the pump. [16] 8. (a) Find an expression for the ratio of the outlet area of the nozzle to the area of the pipe for maximum transmission of power. (b) A pipe of diameter 300 mm and length 3000 m is used for the transmission of power by water. The total head at the inlet of the pipe is 400 m. Find the maximum power available at the outlet of the pipe. Take f = [8+8] 2 of 2

3 Code No: R Set No. 2 III B.Tech I Semester Regular Examinations, November 2008 HYDRAULIC MACHINERY AND SYSTEMS ( Common to Mechanical Engineering and Automobile Engineering) Time: 3 hours Max Marks: 80 Answer any FIVE Questions All Questions carry equal marks 1. A wheel having radial blades has the inner and outer radii of 30 cm and 60cm respectively. The jet enters the blades at the outer tip with a velocity of 40m/s at an angle of 23 0 to the tangent and leaves the blades with a velocity of flow of 8m/s. If the angles of the blades at entrance and exit are respectively 45 0 and 35 0, find the work done per kg of water entering the wheel, the speed of the wheel and its efficiency. [16] 2. A Kaplan turbine develops 1875kW under a head of 6m with overall efficiency of 85%. An elbow type draft tube with inlet diameter 3.5m is provided at runner exit, set 3.0 m above the tail race level, gives a reading of 3N/cm 2 on a vacuum gauge connected to the inlet. Determine the draft tube efficiency. If the output of the turbine is reduced to half, head and speed remain unchanged, what would be the new reading of vacuum gauge after the governing? [16] 3. (a) Show that Pelton Wheel is a low specific speed turbine. (b) What is specific speed? State its significance in the study of hydraulic machines. [8+8] 4. (a) A single acting reciprocating pump running at 30 rpm, delivers 0.012m 3 /s of water. The diameter of the piston is 25 cm and stroke length 50 cm. Determine i. The theoretical discharge of the pump. ii. Co-efficient of discharge and iii. Slip and percentage of the pump. (b) A double acting reciprocating pump, running at 50 rpm is discharging 900 liters of water per minute. The pump has stroke of 400 mm. The diameter of piston is 250 mm. the delivery and suction heads are 25 m and 4 m respectively. Find the slip of the pump and power required to drive the pump. [8+8] 5. (a) What do you mean by manometric efficiency, mechanical efficiency and overall efficiency of a centrifugal pump. (b) The diameters of an impeller of a centrifugal pump at inlet and outlet are 20 cm and 40 cm respectively. Determine the minimum speed for starting the pump if it works against head of 25 m. [8+8] 6. (a) Why are centrifugal pumps used sometimes in parallel and sometimes in series? Draw the following characteristic curves for a centrifugal pump: Head, power and efficiency versus discharge with constant speed. 1 of 2

4 Code No: R Set No. 2 (b) Define cavitation? What are the effects of cavitation? Give the necessary precautions against cavitation. [10+6] 7. (a) The water is supplied at a pressure of 14 N/cm 2 to an accumulator, having a ram of diameter 1.5 m. If the total lift of the ram is 8 m, determine: i. The capacity of the accumulator, and ii. Total weight placed on the ram ( including the weight of ram) (b) A hydraulic press has a ram of 150 mm diameter, plunger of 20 mm diameter. The stroke of the plunger is 200 mm and weight lifted is 800 N. If the distance moved by the weight is 1.0 m in 20 minutes determine: i. The force applied on the plunger, ii. Power required to drive the plunger, and iii. Number of strokes performed by the plunger. [6+10] 8. (a) The rate of flow of water through a pipe of length 1500 m and of diameter 800 mm is 2 m 3 /s. At the end of the pipe, a nozzle of outside diameter 200 mm is fitted. Find the power transmitted through the nozzle if the head of water at the inlet of the pipe is 180 m and f = 0.01 for pipe. (b) The pressure at the inlet of a pipe is 7 MN/m 2. The length of the pipe line is 15 km. Find the diameter of the pipe required if 74 kw power is to be transmitted. Find the η of transmission also. [8+8] 2 of 2

5 Code No: R Set No. 3 III B.Tech I Semester Regular Examinations, November 2008 HYDRAULIC MACHINERY AND SYSTEMS ( Common to Mechanical Engineering and Automobile Engineering) Time: 3 hours Max Marks: 80 Answer any FIVE Questions All Questions carry equal marks 1. 5 cm diameter jet having a velocity of 20m/sec, strikes a flat plate, the normal of which is inclined at 25 0 to the axis of the jet. Calculate the normal force exerted on the plate (a) When the plate is stationary (b) When the plate is moving with a velocity of 10m/sec in the direction of the jet. (c) When the plate is moving with a velocity of 7m/sec parallel to itself and in the direction of the normal to its surface. [4+6+6] 2. An inward flow reaction turbine has outer and inner diameters of the wheel as 1 m and 0.5 m respectively. The vanes are radial at inlet and the discharge is radial. Water enters the vanes at an angle of Assuming the velocity of flow as 3 m/s and constant, find the speed of the wheel and the vane angle at outlet. [16] 3. Define the terms unit head, suction specific speed, unit power, unit speed and unit discharge with reference to a hydraulic turbine. Also derive expressions for these terms. [16] 4. A single acting reciprocating pump has a piston 125 mm in diameter and 260 mm stroke and runs normally at 50 r.p.m. The axis of the barrel is horizontal and 4 m above the level of water in the sump. The suction pipe is 60 mm in diametr, 10 m long and has f= An air vessel is fitted on the suction pipe close to the inlet valve to the cylinder. Calculate the work done during the suction stroke when (a) the pump runs at normal speed with air vessel functioning normally (b) the air vessel is water logged and the pump runs at half the normal speed to avoid knocking. [16] 5. (a) What do you mean by manometric efficiency, mechanical efficiency and overall efficiency of a centrifugal pump. (b) The diameters of an impeller of a centrifugal pump at inlet and outlet are 20 cm and 40 cm respectively. Determine the minimum speed for starting the pump if it works against head of 25 m. [8+8] 6. (a) What do you understand by characteristic curves of a pump? What is the significance of the characteristic curves. 1 of 2

6 Code No: R Set No. 3 (b) Find the number of pumps required to take water from a deep well under a total head of 89 m. All the pumps are identical and are running at 800 r.p.m. the specific speed of each pump is given as 25 while the rated capacity of each pump is 0.16 m 3 /s. [8+8] 7. (a) A hydraulic lift raises a load of 80 kn through a height of 12 m once after every two minutes. The speed of the lift is 60 cm/sec. the lift is operated by an accumulator which is continuously charged by a pump. The pressure of water is 4.5 bar. Take pump η = 0.85 and lift η = Find the power required to drive the pump and maximum capacity of accumulator. Neglect friction losses. (b) A hydraulic press, operated by a lever has 3 cm diameter plunger and leverage is 10. Find the diameter of ram required to raise the load 15 MN when the force applied is 20 kn at the free end of lever. Assume that losses are 20%. [10+6] 8. (a) A pipe line of length 2000 m is used for power transmission. If kw power is to be transmitted through the pipe in which water having a pressure of N/ cm 2 at inlet is flowing. Find the diameter of the pipe and efficiency of transmission if the pressure drop over the length of pipe is 98.1 N/ cm 2. take f = (b) Find the maximum power transmitted by a jet of water discharging freely out of nozzle fitted to a pipe of 300 m long and 100 mm diameter with co-efficient of friction as The available head at the nozzle is 90 m. [10+6] 2 of 2

7 Code No: R Set No. 4 III B.Tech I Semester Regular Examinations, November 2008 HYDRAULIC MACHINERY AND SYSTEMS ( Common to Mechanical Engineering and Automobile Engineering) Time: 3 hours Max Marks: 80 Answer any FIVE Questions All Questions carry equal marks 1. Show that for a curved radial vane, the work done per second is given by ρav 1 [V w1 u 1 ± V w2 u 2 ]. [16] 2. Write short notes on: (a) Scroll casing (b) Turbine efficiencies (c) oil pressure regulator (d) Electro hydraulic governor. [16] 3. (a) What are unit quantities. Define the unit quantities for a turbine. Why are they important? (b) A water turbine develops 175 hp at 230r.p.m. under a head of 16m. Determine the scale ratio and the speed of a similar machine which will generate 900 h.p working under a head of 25 m. [8+8] 4. Derive expressions for the accelerations and friction head impressed on the water in the suction and delivery pipes. Sketch indicator diagram and determine the work done per stroke of the pump. [16] 5. (a) Define a centrifugal pump. Explain the working of a single-stage centrifugal pump with sketches. (b) The internal and external diameters of the impellers of a centrifugal pumps are 300 mm and 600 mm respectively. The pump is running at 1000 r.p.m. The vane angles at inlet and outlet are 20 o and 30 o respectively. The water enters the impeller radially and velocity of flow is constant. Determine the work done by the impeller per unit weight of water. [8+8] 6. (a) How the model testing of the centrifugal pumps are made. (b) The diameter of an impeller of a centrifugal pump at inlet and outlet are 30 cm and 60 cm respectively. Determine the minimum starting speed of the pump if it works against a head of 30 m. [8+8] 7. A hydraulic lift is required to lift a load of 12 kn through a height of 10 m, once in every 1.75 minutes. The speed of the lift is 0.75 m/s. During working stroke of the lift, water from accumulator and the pump at a pressure of 400 N/ cm 2 is supplied to the lift. If the efficiency of the pump is 80% and that of lift 75%, find the power required to drive the pump and the minimum capacity of the accumulator. Neglect friction losses in the pipe. [16] 1 of 2

8 Code No: R Set No (a) A pipe of diameter 300 mm and length 3500 m is used for the transmission of power by water. The total head at the inlet of the pipe is 500 m. Find the maximum power available at the outlet of the pipe, if the value of f= (b) A nozzle is fitted at the end of a pipe of length 300 m and of diameter 100 mm. For the maximum transmission of power through the nozzle, find the diameter of nozzle. Take f = [8+8] 2 of 2