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Mechanical Technology Question Paper
Mechanical Technology
Course:Diploma In Mechanical Engineering
Institution: Mombasa Polytechnic University College question papers
Exam Year:2004
2101/303
2102/303
2103/303/
2104/303
2105/303
2106/303
2107/303
2108/303
MECHANICAL TECHNOLOGY
Oct/Nov. 2004
Time: 3 Hours
THE KENYA NATIONAL EXAMINATIONS COUNCIL
DIPLOMA IN MECHANICAL ENGINEERING (PRODUCTION OPTION)
DIPLOMA IN MECHANICAL ENGINEERING (PLANT OPTION)
DIPLOMA IN AUTOMOTIVE ENGINEERING
DIPLOMA IN CONSTRUCTION PLANT ENGINEERING
DIPLOMA IN AGRICULTURAL ENGINEERING
(FARM POWER AND MACHINERY OPTION)
DIPLOMA IN MECHANICAL ENGINEERING
(FABRICATION TECHNOLOGY AND METALLURGY OPTION)
DIPLOMA IN AERONAUTICAL ENGINEERING
(ENGINES AND AIR FRAMES OPTION)
DIPLOMA IN MECHANICAL ENGINEERING
(MARERIALS TECHNOLOGY AND METALLURGY OPTION)
MECHANICAL TECHNOLOGY
3 Hours
INSTRUCTIONS TO CANDIDATES:
You should have the following for this examination:
Answer booklet
Mathematical table/calculator
Thermodynamic & Transport properties of Fluids tables, by Rogers & mayhew.
This paper contains four sections, A,B,C and D.
Answer any ONE question from each of the sections A, B and C and any TWO questions from section D.
All questions carry equal marks.
Maximum marks for each part of a question are shown.
This paper consists of 7 printed pages.
SECTION A: (MECHANICS OF MACHINES)
Answer any ONE question from this section.
The following data refers to a vehicle:
Mass of the vehicle=1600kg
Number of wheels =4
Moment of inertia of each wheel=3.2kgm2
Diameter of each wheel=650mm
Mass of engine rotating parts=60kg
Radius of gyration of engine rotating parts=90mm
Transmission efficiency=85%
Gear ration from engine to back axle=6
The resistance to motion is given by (180 + 0.84V2) and the engine torque available is given by (90 - 0.048V2), where V is the linear speed of the vehicle in m/s.
Determine:
The power of the vehicle when velocity is 18m/s.(11 marks)
The time taken for the vehicle to increase speed from 18m/s to 24 m/s.(5 marks)
The distance covered during the acceleration(4 marks)
a) i) State TWO conditions necessary for complete dynamic balance for a shaft carrying several masses.
ii) State any FOUR effects of unbalanced forces in a machine having several rotating parts.(4 marks)
b) Four masses A,B,C and D are carried on a shaft with their centers of mass 150mm, 200mm, 700mm and 600mm respectively. The masses are such that A=9kg, B=18kg, C=21kg and D=14kg. The distance of the planes of rotation measured from mass A are anticlockwise from A are B=3m, C=5m and D=7m respectively. The angular position of B,C and D measured anticlockwise from A, are 750, 1600 and 2400 respectively. Two balance masses are fitted as follows: one, midway between A and B, whose centre of mass from the shaft axis is 110mm; and the other is fitted mid-way between C and D, whose centre of mass from the shaft axis is 90mm.
Determine the values of the balance masses and their angular positions with respect to A. show the position of the masses on an end view. (16marks)
SECTION B: STRENGTH OF MATERIALS
Answer any ONE question from this question.
The following data refers to an open – coiled helical spring:
Pitch of the coils=27mm
Number of coils=12
Mean coil diameter=54mm
Diameter of wire=8mm
Modulus of elasticity spring material=208GN/m2
Modulus of rigidity of spring material=72GN/m2
The spring is subjected to a pure axial twisting moment of 9M-m.
Determine:
The resulting angle of twist. (8 marks)
The extension produced. (31/2 marks)
The bending stress in the surface of the wire. (41/2 marks)
The shear stress in the surface of the wire. (4 marks)
a) i) State any FOUR assumptions made in the theory of torsion.
ii) Show that the strain energy ‘u’ stored in a solid shaft of diameter ‘d’, length ‘l’ and modulus of rigidity G, when subjected to pure torque T, is given by the expression:
u=T2 x Volume of the shaft
4G
where T is the maximum shear stress. (7 marks)
b) A composite shaft is used to transmit 380KW at a speed of 750 rev/min. The composite shaft is made by passing a solid cylindrical shaft of 65mm diameter and 1.8m long, 65mm and 75mm internal and external diameters respectively. They are then rigidly joined together at their ends. The solid shaft is made of steel and the hollow shaft is made of brass.
Determine:
The maximum and minimum stresses in the two shafts.
The angle of twist.
The total strain stored:
Take G for brass=35GN/m2
and G for steel=78 GN/m2 (13 marks)
SECTION C: FLUID MECHANICS
Answer any ONE question from this section.
a) Explain the following terms:
Geometrical similarity
Dynamic similarity (3 marks)
b) Show from the first principles the requirements for dynamic similarity between two fluid motions when considering:
Viscous resistance
Wave resistance (6 marks)
The air resistance R of a supersonic plane during flight, is a function of its length L, velocity V, air dynamic velocity µ, air density ?, and bulk modulus K. Show that the air resistance R is given by:
R=pl^2 V^2Ø{µ/pvl ,k/(pv^2 )}
where Ø means a “function of”. (11 marks)
a) i) Define the following terms with reference to fluid flow:
Critical velocity
Reynold’s number
ii) Show that the flow rate Q, of a fluid of dynamic viscosity ?, flowing under laminar conditions through a horizontal circular pipe of diameter ‘d’, length ‘L’, with a mean velocity V, when the pressure difference between the ends is P, is given by the expression:
Q=(ppd^4)/128?L
Hence show that the pressure difference p can be given by the expression
P=32?lv/d^2 (121/2 marks)
b) Oil is pumped through a pipe 120mm diameter and 900m long. The pressure difference between the ends is 420KN/m2. The dynamic viscosity of the oil is 1.42 N-S/m2 and the relative density is 0.9.
Show that the flow is viscous if Reynold’s number is 2100.
Calculate the electric power of the motor required if the mechanical efficiency between the pump and the electric motor is 80%.
SECTION D: THERMODYNAMICS
Answer any TWO questions from this section.
a) Show that the diagram efficiency, ?_d, of an impulse turbine is given by:
?_d=4b/a_i (cos??a_i- b/a_i ? )
Where b=mean blade speed
a_i=nozzle angle
ai=absolute velocity of steam from nozzle. (7 marks)
b) The following data applies to the first stage of an impulse turbine which is a two-row velocity compounded wheel:
Turbine speed=2000rev/min
Mean blade radius=600mm
Nozzle angle=200
Exit angle from first row moving blade=220
Exit angle from second row moving blade=340
Blade velocity coefficient for all blades=0.9
Mass flow rate of steam=6kg/s
Absolute of steam at discharge from the nozzle=700m/s
Exit angle from fixed blade=270
Determine the:
Blade inlet angle for each row.
Diagram power. (13 marks)
a) Show that the logarithmic mean area Am of a cylinder of unit length, internal radius r1, external radius r2, thermal conductivity k, whose inside and outside surface temperature are t1 and t2 respectively are given by:
A_m=(2p(r_2-r_1))/(l_n r_2/r_1 ) (6 marks)
b) Wet steam at 20 bar is carried in a steel steam mains of outside diameter 140mm, thickness 6mm and length 8m. The mains is insulated with an inner layer of diatomaceous earth 38mm, and an outer layer of magnesia 30mm thick. The inside heat transfer coefficient is 8.5 W/m2K and that of the outside surface lagging is 18W/m2K. The thermal conductivities of the diatomaceous earth, magnesia and steel are 0.09, 0.06 and 48W/mK, respectively.
Determine:
The rate of heat loss.
The temperature of the outside surface of the lagging. (14 marks)
a) i) With the aid of a graph show how the indicated power and brake power vary with the engine speed for a variable speed engine and explain the general shape of the graph.
ii) State any FOUR advantages of super charging of an internal combustion engine. (51/2 marks)
b) Briefly describe the Morse Test for measuring the indicated power of a multi-cylinder engine. (5 marks)
c)A four-cylinder petrol engine has an output of 16.5KW at a speed of 2400 rev/min. A Morse Test is carried out and the brake torque readings are 112 N, 107N, 105N and 109N respectively. The torque arm has a length of 0.4m and the fuel consumption is 8 litres per hour. The specific gravity of the fuel is 0.8 and the calorific value is 45MJ/kg.
Determine:
The brake thermal efficiency
The specific fuel consumption on brake power basis. (91/2 marks)
a) Explain the following terms as applied to a spark ignition engine:
“rich mixture”
“weak mixture” (2 marks)
b) Distinguish between higher and lower calorific values of a fuel. (2 marks)
c)The dry exhaust gas analysis by volume during a test on an engine was 11% CO2, 1.8O2, 3.2CO and the remainder was nitrogen. The flue gases were exhausted to the atmosphere at a pressure of 1.013 bar, temperature of 3250C and at a velocity of 8m/s. The fuel had a composition by mass:- 85.8% carbon, Hydrogen 14.2%. The total mass of fuel burnt was 4kg/hr.
Determine:
The air/fuel ratio by mass
The mixture strength
The exhaust pipe diameter.
Take R=290J/kgK. (16 marks)
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