337514(37)
B.E (Fifth Semester) Examination,
Nov.-Dec., 2008
(Mechanical Branch)
FLUID MACHINERY
Time allowed : Three Hours
Maximum Marks : 80
Minimum Pass Marks : 28
- (a) List the various velocity distribution laws followed in laminar Boundary Layer. 2
Answer any two question from the following:
(b) Air is flowing over a flat plate 5 m long and 2.5 m wide with a velocity of 4 m/s at 15 degree C. If density of air is taken as 1.2 kg/m3 and kinematic viscosity of air as 1.47 x 10-5 m2/s. Calculate:
(i)Length of plate over which the boundary layer is laminar and thickness of the boundary layer.
(ii) Shear stress at the location where boundary layer ceases to be laminar.
(iii)Total drag force on both sides on the portion of plate where boundary layer is laminar.
(c) In a wind tunnel experiments were conducted with a wind speed of 50 kgm/h on a flat plate of size 2m long and 1m wide. The mass density of air 1.15kg/m3. The plate is kept at an angle such that co-efficients of lift and drag are 0.75 and 0.15 respectively.
Determine:
i) Lift force
ii) Drag force
iii) Resultant force
iv) Power encerted by the air stream on the plate.
(d) Obtain an expression for lift force produced on a rotating cylinder place in a uniform flow field such that the axis of the cylinder is perpendicular to the direction of flow. - Part (a) is compulsory:
(a) What is the condition for hydraulic efficiency of a Pelton wheel to be maximum? Write the expression for maximum hydraulic efficiency of a Pelton wheel. 2
Answer any two question from the following:
(b) Prove that the work done per second on a series of moving curved vanes by a jet of water striking at one of the tips of the vane is given by
work done/sec =ƍaV1[Vw1± Vw2]u
where ƍ= density of water. 7
(c) A Pelton wheel is to be designed for the following specifications:
Power(brake or shaft) = 9560 kW
Head = 350 mSpeed = 750 rpm
Overall efficiency = 85%
Jet diameter = not to exceed 1/6 th of wheel diameter
Determine the followings:
i. The wheel diameter
ii. Diameter of the jet
iii. The number of jets required
Take Cv = 0.985, speed ratio =0.45
where Cv= coefficint of velocity. 7
(d) With the help of a neat diagram, explain the construction and working of a Pelton wheel turbine. 7 - Part (a) is compulsory:
(a) Define specific speed of a turbine. Write down the formula. 2
Answer any two questions from the following:
(b) What is Cavitation? Explain in detail how this can be avoided in reaction turbines.7
(c) The internal and external diameters of an inward flow reaction turbine are 0.8 m and 1.2 m respectively. The width of the wheel at inlet and outlet is 150 mm. the head on the turbine is 10 m and the hydraulic efficiency is 92%. The vane angle outlet is 20 degree. Final discharge at outlet is radial at a velocity of 3 m /s. Find:
i. The guide blade angle.
ii. The runner vane angle at inlet .
iii. The speed of the turbine.
iv. The discharge of the turbine.
v. The runner power
Draw a neat velocity triangle. 7
(d) A kalpan turbine works under a head of 22 m and runs at 150 rpm. The diameters of the runner and boss are 4.50 meters and 2 meters respectively. The flow ratio is 0.43. The inlet vane angle at the extreme edge of the runner is 160 degree. If the turbine discharges radially at outlet, determinethe discharge, the hydraulic effeciency, the guide blade angle at the extreme edge of the runner and the outlet vane angle at the extreme edge of the runner, with the help of a neat velocity triangle. - Part (a) is compulsory :
(a) Write down the various expressions for manometric head of centrifrugal pumps.2
Answer any One question from (b) and (c):
(b) A centrifugal pump is to discharge 0.118 m3/s at a speed of 1450 rpm against a head of 25 m. The impeller diameter is 250 mm, its width at outlet is 50 mm and manometric efficiency is 75%. Determine vane angle at the outer periphery of the impeller.Draw a neat velovity triangle. 10
OR
(c) How can you determine the minimum speed required to start a centrifugal pump? Derive. 10
