Labels: , ,
Monday 15 October 2012

Question bank download for Fluid Mechanics and Machinery


ME 34 Fluid Mechanics and Machinery – Question Bank
Unit –I
  1. Calculate the capillary effect in millimetres in a glass tube of 4 mm diameter, when immersed in (1) water and (2) mercury the temperature of the liquid is 20°C and the values of surface tension of water and mercury at 20°C in contact with air are 0.0735 N/m and 0.51 N/m respectively. The contact angle for water θ = 0 and for mercury θ = 130°. Take specific weight of water at 200 C as equal to 9790 N/m3 and specific gravity of mercury is 13.6.
  2. What do you mean by surface tension? If the pressure difference between the inside and outside of the air bubble of diameter, 0.01 mm is 29.2 kPa, what will be the surface tension at air water interface? Derive an expression for the surface tension in the air bubble and from it, deduce the result for the given conditions.
  3. An orificemeter with orifice diameter 15 cm is inserted in a pipe of 30 cm diameter. The pressure of the upstream and downstream of orificemeter is 14.7 N/cm2 and 9.81 N/cm2. Find the discharge, if Cd = 0.6.
  4. A horizontal venturimeter with inlet and throat diameter 300 mm and 100 mm respectively is used to measure the flow of water. The pressure intensity at inlet is 130 kN/m2 while the vacuum pressure head at throat is 350 mm of mercury. Assuming that 3 percent head lost between the inlet and throat. Find the value of coefficient of discharge for the venturimeter and also determine the rate of flow.
  5. The velocity distribution over a plate is given by u=(3/4)y-y^2 where u is velocity in m/s and at a depth y in m above the plate. Determine the shear stress at a distance of 0.3 m from the top of plate. Assume dynamic viscosity of the fluid is taken as 0.95 N s/m2.
  6. The space between two square parallel plates is filled with oil. Each side of the plate is 75 cm. The thickness of the oil film is 10 mm. The upper plate which moves at 3 m/s requires a force of 100 N to maintain the speed. Determine:(1) The dynamic viscosity of the oil(2) The kinematic viscosity of the oil, if the specific gravity of oil is 0.9.
  7. Calculate the capillary effect in a glass tube 5 mm diameter, when immersed in (1) water and (2) mercury. The surface tension of water and mercury in contact with air are 0.0725 N/m 0.51 N/m respectively. The angle of contact of mercury is 130°.
  8. Calculate the pressure exerted by 5 kg of nitrogen gas at a temperature of 10°C when the volume is 0.4 m3. Also find the volume when the pressure is 3x 105 N/m2 and the temperature is 10°C. Assume Ideal gas law is applicable.
  9. A rectangular plate of size 25 cm x 50 cm and weighing 245.3 N slides down a 300 inclined surface at a uniform velocity of 2 m/s. If the uniform 2 mm gap between the plate and the inclined surface is filled with oil determine the viscosity of the oil.
  10. Determine the minimum size of glass tubing that can be used to measure water level. If the capillary rise in the tube is not to exceed 2.5 mm. Assume surface tension of water in contact with air as 0.0746 N/m.
  11. At a depth of 2 kIn in the ocean the pressure is 82404 kN/m2. Assume the specific weight at the surface as 10055 N/m3 and that the average bulk modulus of elasticity is 2.354 x 109 N/m2 for that pressure range. Determine the change in specific volume between that at surface and 2 km depth and also determine the specific weight at that depth?
  12. A venturimeter is inclined at 60 degree to the vertical and its 150 mm diameter throat is 1.2 m from entrance along its length. It is fitted to a pipe of diameter 300 mm diameter pipe. The pipe conveys gasoline of specific gravity 0.82 and flowing 0.215 m3/s upwards. Pressure gauge inserted at entrance and throat show the pressures of 0.141 N/mm2 and 0.077 N/mm2 respectively. Determine the coefficient of discharge of the venturimeter. Also determine the reading in mm of differential mercury column, if instead of pressure gauges the entrance and the throat of venture meter are connected to the limbs of a U tube mercury manometer.
  13. What is the bulk modulus of elasticity of a liquid which is compressed in a cylinder from a volume of 0.0125 m3 at 80 N/cm2 pressure to a volume of 0.0124 m3 at pressure 150 N/cm2.
  14. A horizontal venturimeter with inlet and throat diameter 300 mm and 100 mm respectively is used to measure the flow of water. The pressure intensity at inlet is 130 kN/m2 while the vacuum pressure head at throat is 350 mm of mercury. Assuming that 3 percent head lost between the inlet and throat. Find the value of coefficient of discharge for the venturimeter and also determine the rate of flow.
  15. The dynamic viscosity of oil, used for lubrication between a shaft and sleeve is 6 poise. The diameter of the shaft is 0.4 m and rotates at 190 rpm. Calculate the power lost in the bearing for a sleeve length of 90 mm. Assume thickness of oil film as 1.5 mm.
  16. In a vertical pipe conveying oil of specific gravity 0.8, two pressure gauges have been installed at 'A' and 'B', where the diameters are 160 mm and 80 mm respectively. 'A' is 2 metres above B. The pressure gauge readings have shown that the pressure at 'B' is greater than at 'A' by 0.981 N/cm2. Neglecting all losses, calculate the flow rate. If the gauges at 'A' and 'B' are replaced by tubes filled with the same liquid and connected to a U-tube containing mercury, calculate the difference in the level of mercury in the two limbs of the U-tube.
  17. Gasoline (sp.gr. = 0.8) is flowing upwards through a vertical pipe line which tapers from 300 mm to 150 mm diameter. A gasoline mercury differential manometer is connected between 300 mm and 150 mm pipe sections to measure the rate of flow. The distance between the manometer tappings is 1 metre and the gauge reading is 500 mm of mercury. Find (1) differential gauge reading interms of gasoline head (2) rate of flow. Assume frictional and other losses are negligible.
  18. U-tube manometer containing mercury was used to find the negative pressure in the pipe, containing water. The right limb was open to the atmosphere. Find the vacuum pressure in the pipe, is the difference of mercury level in the two limbs was 100 mm and height of water in the left limb from the centre of the pipe was found to be 40mm below.
  19. State if the flow represented by u=3x+4y and v=2x-3y is rotational or irrotational. Find the potential function, if the flow is irrotational and vorticity, if it is rotational.
  20. In a pipeline water is flowing. A manometer is used to measure the pressure drop for flow through the pipe. The difference in level was found to be 20 cm. If the manometric fluid is CCl4 (density=1.596 g/cm3). Find the pressure drop in S.I units. If the manometric fluid is changed to mercury (density=13.6 g/cm3). What will be the difference in level.
  21. The maximum blood pressure in the upper arm of a healthy person is about 120 mmHg. If a vertical tube open to the atmosphere is connected to the vein in the arm of the person, determine how high the blood will rise in the tube. Take the density of the blood to be 1050 kg/m3.



Unit II

  1. State Bernoulli's theorem for steady flow of an incompressible fluid. (4)
  2. Derive an expression for Bernoulli's equation. (12)
  3. A horizontal venturimeter with inlet and throat diameter 300 mm and 100 mm respectively is used to measure the flow of water. The pressure intensity at inlet is 130 kN/m2 while the vacuum pressure head at throat is 350 mm of mercury. Assuming that 3 percent head lost between the inlet and throat. Find the value of coefficient of discharge for the venturimeter and also determine the rate offlow. (16)
  4. List out Minor losses in flow through pipes. (3)
  5. Derive Darcy Weisback equation for head loss due to friction in flow through pipe. (13)
  6. Distinguish between pipes connected in series and parallel? (4)
  7. A pipe of 0.6 m diameter is 1.5 kIn long. In order to augment the discharge, another line of the same diameter is introduced parallel to the first in the second half of the length. Neglecting minor losses.Find the increase in discharge if f=0.04.The head at inlet is 40 m.
  8. State and derive impulse momentum equation. (6)
  9. Water is flowing through a tapering pipe of length 200 m having diameters 500 mm at the upper end and 250 mm at the lower end, the pipe has a slope of 1 in 40. The rate of flow through the pipe is 250 lit/sec. The pressures at the lower end and at the upper end are 20 N/cm2 and 10 N/cm2 respectively. Determine the loss of head and direction of flow. (16)
  10. A horizontal pipe of 400 mm diameter is suddenly contracted to a diameter of 200 mm. The pressure intensities in the large and small pipe is given as 15 N/cm2 and 10 N/cm2 respectively. Find the loss of head due to contraction, if Cc = 0.62, determine also the rate of flow of water.
  11. Air is flowing over a flat plate with a velocity of 5 m/s. The length of the plate is 1.5 m and width 1 m. The kinematic viscosity of air is given as 0.15 x 10-4 m2/s. Find: (i) the boundary layer thickness at the end of plate (5) (ii) shear stress at 20 cm from the leading edge and (6) (ill) drag force on one side of the plate. (5) Take the velocity profile over a plate as u/U=sin(1l/2xy/li) and the density of air 1.24 kg/m3.
  12. Two pipes of diameter 400 rom and 200 rom are each 300 m long. Where the pipes are connected in series the discharge through the pipe line is 0.10 m3/s. Find the loss of head. What would the loss of head in the system to pass the same total discharge when the pipes are connected in parallel? Assume Darcy's friction factor as 0.0075.
  13. For flow of viscous fluids through an annulus derive the following expressions: (1) discharge through the annulus and (2) shear stress distribution. (12) -(ii) Define momentum thickness and energy thickness. (4)


Unit-III DIMENSIONAL ANALYSIS

Part-A

  1. State the Buckingham's π theorem.
  2. What are the similarities between model and prototype?
  3. What is scale effect in physical model study?
  4. Explain the term dimensionally homogeneous equation.
  5. What is meant by undistorted models?
  6. What is similarity in model study?
  7. Define dimensional homogeneity and also give example for homogeneous equation?
  8. What do you mean by fundamental units and derived units? Give examples.
  9. What do you mean by repeating variables? How they are selected.
  10. What do you mean by dimensionless numbers? Name any four dimensionless numbers.

Part –B

  1. Using Buckingham's π theorem, show that the velocity through a circular orifice is given byV=√2gH∅[D/H,μ/ρVH], where H is the head causing flow, D is the diameter of the orifice, µ is co-efficient of viscosity, ρ is the mass density and g is the acceleration due to gravity.
  2. The frictional torque T of a disc of diameter D rotating at a speed N in a fluid of viscosity μ and density ρ in a turbulent flow is given by T=D5 N2 ρφ[μ/(D2 Nρ)]. Prove this is by method of dimensions.
  3. Using Buckingham’s π- theorem, shown that the discharge Q consumed by an oil ring is given by Q=Nd^3∅[μ/(ρNd^2 ),σ/(ρN^2 d^3 ),ω/(ρN^2 d)]where d is the internal diameter of the ring, N is rotational speed, is density, μ is viscosity, is surface tension and is the specific weight of oil.
  4. The pressure difference ∆p in a pipe of diameter D and length L due to viscous flow depends on the velocity V, viscosity μ and density ρ. Using Buckingham's π theorem, obtain an expression for ∆p.
  5. Explain the different types of similarities that must exist between a prototype and its model.
  6. The ratio of lengths of a sub-marine and its model is 30:1. The speed of sub-marine (prototype) is 10m/s. The model is to be tested in a wind tunnel. Find the speed of air in wind tunnel. Also determine the ratio of the drag (resistance) between the model and its prototype. Take the value of kinematic viscosities for sea water and air as 0.012 stokes and 0.016 stokes respectively. The density for sea- water and air is given as 1030 kg/m3 and 1.24 kg/m3 respectively.
  7. In a 1 in 20 model of stilling basin, the height of the hydraulic jump in the model is observed to be 0.20 metre. What is the height of the hydraulic jump in the prototype? If the energy dissipated in the model is 1/10kW, what is the corresponding value in prototype?
  8. A 1:64 model is constructed of an open channel in concrete which has manning’s N=0.014. Find the value of N for the model.
  9. A 7.2m heigh and 15m long spillway discharges 94 m3/s discharge under a head of 2.0m. if a 1:9 scale model of this spillway is to be constructed, determine model dimensions, head over spillway model and the model discharge. If model experiences a force of 7500N (764.53 kgf), determine force on the prototype.


Unit –IV- ROTO DYNAMIC MACHINES

Part-A (2 Marks)

  1. Explain specific speed.
  2. Classify turbines according to flow.
  3. What is the role of a volute chamber of a centrifugal pump?
  4. Write the equation for specific speed for pumps and also for turbine.
  5. Distinguish between centrifugal pump and reciprocating pump.
  6. Draw a sketch of a Francis turbine and name its components.
  7. Write the function of draft tube in turbine outlet?
  8. Distinguish between pumps in series and pumps in parallel.
  9. Draw the characteristics curves of a turbine with head variation
  10. What is draft tube? Why it is necessary in reaction turbine?
  11. How does the specific speed of centrifugal pump differ from that of turbine?
  12. Define hydraulic efficiency.
  13. What is runway speed and specific speed in turbines?
  14. What is positive displacement pump and roto-dynamic pump?
  15. What are the different efficiencies of turbine to determine the characteristics of turbine?
  16. Differentiate between pumps and turbines.
  17. Define indicator diagram. State its uses.

Part-B
  1. What is priming in a centrifugal pump? Why is it necessary? (5)
  2. Give the comparison between impulse and reaction turbine. (8)
  3. In a hydroelectric station, water is available at the rate of 175 m3/s under head of 18 m. The turbine run at a speed of 150 rpm, with overall efficiency of 82%. Find the number of turbines required, if they have the maximum specific speed of 460. (8)
  4. With the help of neat diagram explain the construction and working of a Pelton wheel turbine (8)
  5. What is the condition for hydraulic efficiency of a Pelton wheel to be maximum? (8)
  6. What is breaking jet in Pelton wheel turbine? (4)
  7. A Pelton wheel has a mean bucket speed of 10 m/s with a jet of water flowing at the rate of 0.7 m3/s under a head of 30 m. The buckets deflects the jet through an angle of 160 degree. Calculate the power given by water to the runner and the hydraulic efficiency of the turbine. Assume coefficient of velocity as 0.98. (12)
  8. A model of a hydro electric power station tail race is proposed to built by selecting vertical scale 1 in 50 and horizontal scale 1 in 100. If the design pipe has flow rate of 600 m3/s and the allowable discharge of 800 m3/s. Calculate the corresponding flow rates for the model testing.(12)
  9. Differentiate Pelton wheel turbine with Francis turbine. (3)
  10. A 50 m/s velocity jet of water strikes without shock, a series of vanes moving at 15 m/s. The jet is inclined at an angle of 20 degrees to the direction of motion of vanes. The relative velocity of jet at outlet is 0.9 times of the values at inlet and the absolute velocity of water at exit is to be normal to the motion of vanes. Determine the vane angle at entrance and exit. Also determine work done on vanes per second per N of water supplied by the jet. (13)
  11. The nozzle of a Pelton wheel gives a jet of 9 cm diameter and velocity 75 m/s. Coefficient of velocity is 0.978. The pitch circle diameter is 1.5 m and the deflection angle of the buckets is 170 degree. The wheel velocity is 0.46 times the jet velocity. Estimate the speed of the Pelton wheel turbine in rpm, theoretical power developed and also the efficiency of the turbine. (16)
  12. Distinguish between roto-dynamic pump and positive displacement pump with simple sketch. (5)
  13. The following observations are made while conducting a performance test on Centrifugal pump. Determine the overall efficiency of the pump. Discharge of water is 1.8 m3/s. Diameter of suction and delivery pipes are 15 cm and 10 cm respectively. The suction and delivery gauge readings are 25 cm of mercury and 175 kN/m2 respectively. The height of delivery gauge over suction gauge is 0.5 m. The output of driving motor is 9.555 kW.(11)
  14. Define specific speed of a turbine? Derive an expression for the specific speed. (10)
  15. Explain the terms unit power, unit speed and unit discharge with reference to a turbine.(6)
  16. A centrifugal pump having outer diameter equal to 2 times the inner 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 3 m/s. The vanes are set back at an angle of 300 at outlet. If the outer diameter of the impeller is 600 = and width at outlet is 50 =. Determine:
  17. (i) Vane angle at outlet (5) (ii) Work done per second by impeller (6)
  18. (iii) Manometric efficiency. (5)
  19. Derive an expression for the maximum hydraulic efficiency in a impulse turbine. (10)
  20. Compare radial flow and axial flow turbo machines. (6)
  21. Find the power required to derive a centrifugal pump which delivers 0.04 m3/s of water to a height of 20 m through a 15 cm diameter pipe and 100 m long. The overall efficiency of the pump is 70% and coefficient of friction is 0.15 in the formula h = 4fLV2/(2gd). (16)
  22. The velocity of whirl at inlet to the runner of an inward flow reaction turbine is 3.15√H m/s and the velocity of flow at inlet is 1.05√H m/s. The velocity of whirl at exist is 0.22√H m/s in the same direction as at inlet and the velocity of flow at exist is 0.83√H m/s, where H is head of water 30 m. The inner diameter of the runner is 0.6 times the outer diameter. Assuming hydraulic efficiency of 80%. Compute angles of the runner vanes at inlet and exist. (12)
  23. The centrifugal pump has the following characteristics. Outer diameter of impeller = 800 mm; width of the impeller vane at outlet = 100 mm. angle of the impeller vanes at outlet = 40 degree. The impeller runs at 550 rpm and delivers 0.98 m3/s under an effective head of 35 m. A 500 kW motor is used to drive the pump. Determine the manometric, mechanical and overall efficiencies of the pump. Assume water enters the impeller vanes radially at inlet. (13)
  24. A single jet Pelton wheel runs at 300 rpm under a head of 510 m. The jet diameter is 200 mm and its deflection inside the bucket is 165°. Assuming that its relative velocity is reduced by 15% due to friction, determine: (1) water power (2) resultant force on bucket and (3) overall efficiency. (12)
  25. The impeller of a centrifugal pump is 300 mm in diameter and having a width of 50 mm at the periphery. It has blades whose tip angles are inclined backwards at 60° from the radius. The pump delivers 17 m3/min. of water anq the impeller rotates at 1000 rpm. Assuming that the pump is designed to admit liquid radically, calculate: (1) speed and direction of water as it leaves impeller (2) torque exerted by the impeller on water (3) shaft power required (4) lift of the pump. Assume the mechanical efficiency = 95% and the hydraulic efficiency = 75%. (12).


Unit-V- POSITIVE DISPLACEMENT MACHINES

Part-A
  1. Explain specific speed.
  2. When will you select a reciprocating pump?
  3. What is negative slip in a reciprocating pump?
  4. What is similarity in model study?
  5. Distinguish between centrifugal pump and reciprocating pump
  6. What is specific speed of a pump?
  7. Define hydraulic efficiency.
  8. Define slip of reciprocating pump.
  9. What is positive displacement pump and roto-dynamic pump?
  10. What is percentage slip in reciprocating pump?
  11. Define: 'Indicator Diagram'. State its uses.
  12. Differentiate between pumps and turbines.
  13. Define indicator diagram. State its uses.
  14. What is the role of a volute chamber of a centrifugal pump?

Part –B
  1. Describe the working and principles of a reciprocating pump. (11)
  2. Give the comparison between impulse and reaction turbine. (8)
  3. The cylinder bore diameter of a single acting reciprocating pump is 150 rpm and its stroke length is 300 rpm. The pump runs at 50 rpm and lifts water through a height of 25 m. The delivery pipe is 22 m long and 100 mm in diameter. Find the theoretical discharge and the theoretical power required to run the pump. If the actual discharge is 4.2 litres/s, find the percentage slip. (13)
  4. Distinguish between roto-dynamic pump and positive displacement pump with simple sketch. (5)
  5. What is Air vessel and write the expression for workdone by the reciprocating pump fitted with Air vessel. (4)
  6. The Indicator diagram of a single acting reciprocating pump gives effective delivery head of 5 m and 23 m with crank at inner and outer dead centres respectively. What is the static delivery head of the reciprocating pump? (12)
  7. The length and diameter of a section pipe of a single acting reciprocating pump are 5 m and 10 cm respectively. The pump has a plunger of diameter 150 = and of stroke length 300 =. The centre of the pump is 4 m above the water surface in the pump. The atmospheric pressure head is 10.3 m of water and pump is running at 40 rpm. Determine:(i) Pressure head due to acceleration at the beginning of the suction stroke. (6)(ii) Maximum pressure head due to acceleration. (5)(iii) Pressure head in the cylinder at the beginning and at the end of the stroke. (5)
  8. What is a reciprocating pump? Describe the principle and working of a double acting reciprocating pump with a neat sketch. (10)
  9. Define cavitation. What are the effects of cavitation? (6)
  10. Derive an expression for the work saved in a reciprocating pump by using air vessel. (10)
  11. Explain the working of rotary pump and draw the performance curve. (6)
  12. The cylinder bore diameter of a single acting reciprocating pump is 150 mm and its stroke length is 300 mm. The pump runs at 50 rpm. and lifts water through a height of 25 m. The delivery pipe is 22 m long and 100 mm in diameter. Find the theoretical discharge and the theoretical power required to run the pump. If the actual discharge is 4.2 litres/s. Find the percentage slip. (13)
  13. A single-acting reciprocating pump is to raise a liquid of density 1200 kg/m3 through a vertical height of 11.5 metres, from 2.5 metres below pump axis to 9 metres above it. The plunger, which moves with SHM, has diameter 125 mm and stroke 225 mm. The suction and delivery side pipes are 75 mm diameter and 3.5 and 13.5 metres long, respectively. There is a large air vessel fitted on the delivery pipe near the pump axis. But, there is no airvessel on the suction pipe. If separation takes place at 8.829 N/cm2 below atmospheric pressure, find: the maximum speed at which the pump can be run without separation taking place and the power required to drive the pump. Assume there is "no slip" in the pump and f = 0.08 in the friction formula (hf = fLV2/2gd). (16)
  14. A single-acting reciprocating pump has a plunger diameter of 250 mm, and stroke of 450 mm. It is driven at 60 rpm and undergoes SHM. The length and diameter of the delivery pipe are 60 m and 100 rpm, respectively. Determine the power saved in overcoming the friction in the delivery pipe, due to fitting of an air vessel on the delivery side of the pump. Assume the friction factor f = 0.01 the pipe friction formula hf = (flv2/2gd). (10)
  15. The diameter and stroke length of a single-acting reciprocating pump are 75 mm and 150 mm respectively. Supply of water to the pump is from a sump 3 m below the pump through a pipe 5 m long and 40 mm in diameter. The pump delivers the water to a tank located at 12 m above the pump through a pipe 30 mm in diameter and 15 m long. Assuming that separation of flow occurs at 75 kN/m2 (below the atmospheric pressure), find the maximum speed at which the pump may be operated without any separation. Assume that the pis.ton executes a simple harmonic motion. (12)
  16. A double-acting reciprocating pump is running at 30 rpm. Its bore and stroke are 250 mm and 400 mm respectively. The pump lifts water from a sump 3.8 m below and delivers it to a tank located at 65 m above the axis of the pump. The length of suction and delivery pipes are 6 m and 150 m respectively. The diameter of the delivery pipe is 100 mm. If an air vessel of adequate capacity has been fitted on the delivery side of the pump, determine: (1) the minimum diameter of the suction pipe to prevent separation of flow, assuming the m1n1mum head to prevent occurrance of separation is 2.5 m, (2) the maximum gross head against which the pump has to work and the corresponding power of motor. Assume the mechanical efficiency = 78% and slip = 1.5 % ; H atm = 10.0 m ;F = 0.012. (12)

{ 0 comments... read them below or add one }


Post a Comment

Enter your comments here