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CORK INSTITUTE OF TECHNOLOGY
INSTITIÚID TEICNEOLAÍOCHTA CHORCAÍ
Semester 2 Examinations 2010/ Module Title: Fluid Mechanics
Module Code: MECH
School: Mechanical & Process Engineering
Programme Title: Bachelor of Engineering (Honours ) in Mechanical Engineering Bachelor of Engineering (Honours) in Structural Engineering Bachelor of Engineering (Honours) in Biomedical Engineering
Programme Code: EMECH_8_Y CSTRU_8_Y EBIOM_8_Y
External Examiner(s): Mr. John J. Hayes, Prof. Robin Clarke
Internal Examiner(s): Paul D O’Sullivan
Instructions: Attempt any three questions. (33 marks each)
Duration: 2 hours
Sitting: Summer 2011
Requirements for this examination:
Note to Candidates: Please check the Programme Title and the Module Title to ensure that you have received the correct examination paper. If in doubt please contact an Invigilator.
Q
a) A Buoy floating in sea water of density is conical in shape outlined in Fig Q1. Its mass is and its centre of gravity is from the vertex. A flashing beacon is to be fitted to the top with a mass of .What is the maximum height of its centre of gravity above the top of the buoy if the whole assembly is not to be unstable. (The centre of volume of a cone of height h is at a distance 3/4 h from the vertex). (13 marks)
b) Derive an expression for the magnitude and direction of the resultant force on a horizontal reducing pipe bend which deflects the flow of a fluid through an angle , if at entry the pressure is , area , and velocity and at the exit the corresponding values are , , and. (10 marks)
c) Ethanol with a specific gravity of 0.81 enters the reducing bend shown in Fig. Q3 with a velocity of and a pressure of. The bend is in a horizontal plane. Calculate the x and y forces required to hold the bend in place. Neglect energy losses in the bend. (10 marks)
Q
(a) A centrifugal fan delivering 3 m^3 s-1^ of air (density 1.2 kgm-3) runs at 1100 revs min-1. The impeller outer diameter is 70cm and the inner diameter is 48cm. The impeller width at inlet is 16cm and is designed for constant radial flow velocity. The blades are backward inclined making angles of 22.5° and 50° with the tangents at inlet and outlet, respectively. Draw the inlet and outlet velocity triangles and determine the theoretical velocity head produced by the impeller. (13 Marks)
(b) A 60 cm diameter impeller centrifugal impeller has the following characteristics at 750 rev min-1. The pump is used to pump water from one reservoir to another, the water levels between them is 10m. The pipeline is 45 cm in diameter, 130m long, f = 0.005 and it contains 2 gate valves (K = 0.2) and ten 90º bends (K= 0.35). (20 marks) Q[m^3 min-^1 ] 0 7 14 21 28 35 42 49 56 H [m] 40 40.6 40.4 39.3 38 33.6 25.6 14.5 0 [%] 0 41 60 74 83 83 74 51 0
(i) Determine the system characteristic for the pump (ii) Sketch the performance characteristic curve for the pump, (iii) Obtain the flow rate delivered by the pump and the power absorbed.
103 2 4 104 2 4 105 2 4 106 2 4 107 2 4 108 Reynolds Number (logarithmic scale)
Friction Factor
(^) f (logarithmic scale)
0.0006^ 0.
Relative roughness
(^) k / d
Fully developed turbulence - rough pipes
Smooth pipes
critical region
Material k Glass, Brass, Copper, Lead smooth Steel, wrought iron 46 m Ashphalted cast iron 120 m Galvanized iron (^150) m Cast iron 260 m Concrete 3 mm Riveted steel 9 mm
Laminar flow
unstable transition region
