اسئلة امتحان تنافسي
اسئلة امتحان تنافسي
اسئلة امتحان تنافسي
Thermo-Fluids
College of Engr.
Mech. Engr. Dept.
Time: 3 hr
Part I
Note : Answer TEN Questions Only
b- Deaerator
c- Governor
d- Blowdown
e- Cavitation
f- Air-ejector
2. Write down the names of as many types of power generation cycles as you can. Briefly
comment on each one as to efficiency, capacity, application, suitability, fuel . etc.
3. Draw a single stage ideal Rankine cycle for power generation on a T-S diagram. Name and
briefly explain each operation or process and the name of the equipment used in each process.
4. What are the types of turbines used in steam power plant generation systems. Describe the
differences between them. Sketches may be used in your explanation.
b- TDC
c- Bore
e- Octane number
f- Carburator
g- Clearance
d- Crank angle
6. List as many combustion engine cycles as you can and briefly explain two of them. Use P-V
diagrams to help in your explanations.
7. Write as many differences as you can between SI engines and CI engines. Sketches and
equations may be used.
9. Explain briefly FIVE of the following terms ( equations and sketches may be used ) :
a- Internal energy
b- Extensive variable
c- Maxwell relation
e- Gibbs function
f- Diathermal wall
g- Thermodynamic potential
d- Entropy
10. Two processes of heating a certain mass between the same two temperatures T1 & T2 .
The first process is at constant volume and the second process is at constant pressure. Draw
the two processes on a T-S diagram and explain which will require more heat.
11. Show that the efficiency of a Carnot engine is the highest efficiency of any engine.
12. a- Temperature is __________
b- The difference between a superheated vapor and a gas of the same substance is _______
c- An equation of state is ____________
d- A reversible process is ___________
1
Part II
Note : Answer EIGHT Questions Only
(1) What is the physical mechanism of heat conduction in ( a- Solids b- Liquids c- Gases ).
(2) A very high value of Prandtle number is a property of :
a- Air
b- Water
c- Oils
d- Liquid metals
(3) Consider a hot boiled egg in a spacecraft that is filled with air at atmospheric pressure and
temperature at all times. Will the egg cool faster or slower when the spacecraft is in space
instead of on the ground ? Explain
(4) What is a blackbody ? How do real bodies differ from blackbody ?
(5) What are the most important differences between diffusion and radiation ? and how can the
conduction and convection be defined in terms of them ?
(6) What is the criterion used for fully developed temperature profile ? Support your answer
with relations or equations.
(7) Derive the Reynolds analogy between heat and momentum transfer ( St = Cf / 2 ), and
discuss the drawbacks of this analogy.
(8) What is meant by the Time Constant of a thermocouple ? and how can we control its
value ? Explain.
(9) The velocity and temperature profiles of liquid metal flow through a circular tube of radius
( R ), at each axial location is given by :
u (r) = C1
and
T Tw = C2 [ 1 - ( r / R )2 ]
where ( C1 and C2 ) are constants and ( Tw ) is the wall temperature. Evaluate the Nusselt
number of the flow.
(10) Write down the Cartesian form o f the energy equation of conduction heat transfer for
heterogeneous anisotropic continua.
Part III
Q1: Encircle the correct answer:1- A flow in which the quantity of liquid flowing per second is not constant, is called:
a- stream line flow b- turbulent flow c- steady flow d- uniform flow
e- none of these
2- A differential manometer is used to measure:
a- velocity of the liquid b- atmospheric pressure
c- pressure in the pipes and channels
d- pressure in venturimeter
e- none of these
3- Euler equation is based on the assumption that:
a- the fluid is non-viscous
b- the fluid is homogenous and incompressible
c- steady and along the stream line d- the velocity of flow is uniform e- none of the above
4- Reynolds number is the ratio of the inertia force to the:
a- surface tension force b- viscous force c- gravity force d- elastic force e- none of these
5- The stagnation pressure, in an isentropic pipe flow is:
a- remain constant through the pipe b- increases in pipe downstream
c- decreases in pipe downstream
d- decreases in pipe downstream and increases in pipe upstream
e- none of these
6- Flow through a normal shock:
a- stagnation temperature increases
b- stagnation temperature decreases
c- stagnation temperature remains constant
d- stagnation temperature equals stagnation pressure
e- none of these
7- The Mach number in supersonic flow, adiabatic and constant area duct with friction will:
a- increase through the duct towards unity
b- decrease through the duct towards unity
c- be equal through the duct d- increase and decrease thought the duct
e- none of these
8- The cavitation phenomena in a hydraulic machine:
a- causes noise and vibration of various parts
b- makes the blade surface rough
c- Reduces the discharge of a turbine d- all of the above
e- None of the above
9- Pumps in parallel are used :
a- to give high head
b- to give high discharge
c- to pump viscous fluids
d- all of the above
e- none of the above
10- Net positive suction head for the pump depends on:
a- atmospheric pressure only
b- atmospheric pressure and flow velocity only
c- flow velocity only
d- atmospheric pressure, flow velocity and vapor pressure of the fluid only e- none of these
11- The cavitation in a hydraulic machine:
a- causes noise and vibration of various parts
b- makes blades surface rough
c- reduces the discharge of a turbine d- all of the above
e- none of the above
12- For radial flow between parallel discs, the pressure gradient will balance the inertia terms if:
a- Re 0 and causes repelling force between the discs
b- Re and causes repelling force between the discs
c- Re 0 and causes attraction force between the discs
d- Re and causes attraction force between the discs
e- none of these
13- The reversed flow is obtained if:
a- the flow is under zero pressure gradient
b- the negative pressure acts over a sufficient length
c- the positive pressure acts over a sufficient length
d- the favorable pressure acts over a sufficient length
3
e- none of these
14- In potential flow around a body, the drag is:
a- always positive
b- always negative
c- always balance the body force
d- always balance the pressure force
e- always zero
15- In analysis of boundary layer flow, the pressure across the boundary layer:
a- Is zero
b- Is positive
c- Is negative d- Greater than unity e- None of these
( 60 points)
Q2: For a flow over the flat plate, discuss the effects of the positive pressure gradient on length of
laminar portion of the boundary layer, boundary layer thickness and shear stress at the wall.
.... (10 points)
Q3: Use an elemental approach to show that, in pipe flow, the shear stress varies linearly from
zero value at the centerline to maximum value at the surface of the pipe. State all assumptions.
........... (30 points)
University of Baghdad
Applied Mechanics
College of Engr.
Mech. Engr. Dept.
Time: 3 hr
( 34 M )
are :
a)
b)
b) c)
d) )
b) 0.5 , 3
c) 4 , 2
d) 0.5 ,2
4have the same gain , but time constants of 3,4 and 5 seconds
respectively . which responds more quickly to a step input ?
a) They all respond the same since the gain is the same .
b) G1(S)
c) G2(S)
d) G3(S)
5- What are the gain and natural frequency of the following system transfer function
?
a) 36,6
b) 6,6
c) 1,6
d) 6,1
6- The forward feedback and closed loop transfer function for the system are:
a)
b)
c) 1.5
d) 2
9- The percentage overshoot of a second order system to a step input depends only on :
a) the value of the step input
b) the value of the damping ratio
c) the value of the gain k
d) the parameter
10 What are the pole p , and zero , z , of the transfer function
a)
11 Draw the root- locus plot and write the characteristic equations for the following systems
15 What are the types of frequency, write the formula for each type with units.
16 Consider a single degree of freedom system with mass , spring and viscous damping excited
by a harmonic force . draw the curves between the amplitude and the phase angle against
frequency ratio
where is the effect of damping ratio on the amplitude and phase ?
17 What are the facts of the rigid body mode?
M)
1.
Draw the free-body diagram of member AB then list the number of unknowns.
2.
Describe the procedure for finding out the stresses in a composite bar.
3.
4.
Write a note on the influence of various factors of the endurance limit of a ductile material.
5. When the shaft is subjected to fluctuating loads, what will be the equivalent twisting moment
and equivalent bending moment ?
6.
7.
How do you express the life of a bearing? What is an average or median life?
8. Explain the different causes of gear tooth failures and suggest possible remedies to avoid such
failures.
If the sum of all the forces acting on a moving object is zero, the object will:
10. Maximum shear stress theory (also known as Guests or Trescas theory is mostly used for
designing members of:
(a) Ductile material (b) Brittle material (c) Composite material (d) Non of the above
11. The ratio of linear stress to linear strain is called:
(a) Modulus of elasticity (b) Modulus of rigidity (c) Bulk modulus
12. The modulus of elasticity for mild steel is approximately equal to:
(a) 80 kN/mm2 (b) 100 kN/mm2 (c) 110 kN/mm2 (d) 210 kN/mm2
13. An aluminum member is designed based on:
(a) yield stress (b) elastic limit stress
(c) proof stress
3
14. In a body, a thermal stress is one which arises because of the existence of:
(a) Latent heat (b) Temperature gradient
(c) Total heat
(d) Specific heat
15. The stress in the bar when load is applied suddenly is ............. as compared to the stress
induced due to gradually applied load.
(a) same
(b) double
(c) three times
(d) four times
16. Two shafts under pure torsion are of identical length and identical weight and are made of
same material. The shaft A is solid and the shaft B is hollow. We can say that:
(a) shaft B is better than shaft A
(b) shaft A is better than shaft B
(c) both the shafts are equally good
17.The maximum shear stress developed in a beam of rectangular section is ........ the average
shear stress.
(a) equal to (b) 3/4 times (c) 1.5 times
18. In case of pressure vessels having open ends, the fluid pressure induces:
(a) Longitudinal stress (b) circumferential stress (c) Shear stress (d) none of these
19. The endurance or fatigue limit is defined as the maximum value of the stress which a polished
standard specimen can withstand without failure, for infinite number of cycles, when subjected to
(a) static load (b) dynamic load (c) static as well as dynamic load (d) completely reversed load
(c)
Throat of weld
24. When a nut is tightened by placing a washer below it, the bolt will be subjected to:
(a) tensile stress
(b) compressive stress
(c) shear stress
(d) none of these
25. In a steam engine, the piston rod is usually connected to the crosshead by means of a:
(a) knuckle joint
(b) universal joint
(c ) flange coupling
(d) cotter joint
26. A keyway lowers:
(a) the strength of the shaft (b) the rigidity of the shaft
(c) both the strength and rigidity of the shaft
(d) the ductility of the material of the shaft
27.Which of the following loading is considered for the design of axles ?
(a) Bending moment only (b) Twisting moment only (c) Combined bending moment and torsion
(d) Combined action of bending moment, twisting moment and axial thrust
28. The power transmitted by means of a belt depends upon:
4
30. When a helical compression spring is subjected to an axial compressive load, the stress induced
in the wire is:
(a) tensile stress
(b) compressive stress
(c) shear stress
(d) bending stress
31. sliding bearing which can support steady loads without any relative motion between the
journal and the bearing is called:
(a) zero film bearing
(b) boundary lubricated bearing
(c) hydrodynamic lubricated bearing
(d) hydrostatic lubricated bearing
32. The static tooth load should be ........... the dynamic load.
(a) less than
(b) greater than
(c) equal to
33. The size of gear is usually specified by:
(a) pressure angle
(b) pitch circle diameter
For polar coordinates, the Airy stress function can be modified to get r = --------------------
= ------------------------------------------
and r = --------------------------------------------4-
The material in complex stress analysis could be failed if the yield stress of the material
while between true strain and engineering strain is ----------------------------------------------------------Q2) Detect the sentences if it is FALSE or TRUE and correct the false ones :1-
The collision of two bodies of masses m1 , m2 and initial velocities u1 , u2 and final velocities
v1 , v2 in opposite directions is
2-
3-
In pressure vessel of diameter (d) and thickness (t) is the max principle stress 1 = 2
4-
5-
The relation between plastic stress and plastic strain in the plastic deformation of a body is
What is the conservation of momentum for two bodies have mass moment of inertia I1,I2 ,
What are the acceleration components of the sliding link in four bar mechanism ?
3-
What is the value of the plastic stress for a material linear elastic linear work hardening ?
4-
What is the collapse load for a simply supported beam of length l with mid plane load p ?
5-
What are the portal frame ? and how could we find the modes of failure ?
University of Baghdad
Thermo-Fluids
College of Engr.
Mech. Engr. Dept.
Time: 3 hrs.
b- 78 N lift
c- 7.8 N drag
d- 7.8 N lift
(4) The friction factor in a (2.5 cm) diameter pipe is (0.02). The pipe length is (10 m) and the
velocity is (4 m/s) of water. Calculate the pressure drop over the pipe.
(5) In supersonic isentropic flow of a perfect gas, an increase in area causes:
a-Increase in velocity
b-Diverging passage
c-Converging-diverging passage
e-Outward flow
reaction turbine
(9) A Francis turbine is an outward flow reaction turbine:
(10) A Kaplan turbine is an axial flow reaction turbine:
(11) A draft tube is used with Impulse turbine:
a- True
a-True
a-True
b-False
b-False
b-False
(12) The performance of air compressor at high altitude will be _______ as compared to that at
sea level:
a-Same
b-Lower
c-Higher
(13) What are the basic modes of heat transfer ? and what are the basic laws which are used to
calculate the heat transfer rate in each mode ?
(14) A very low value of Prandtle number is a property of _______ :
a- Air
b- Water
c- Oils
d- Liquid Metals
c- Forced Convection
(16) What are the most important dimensionless numbers in each of the following phenomena :
a- Natural convection heat transfer in incompressible fluids
b- Forced convection heat transfer in incompressible fluids
1
a- Adiabatic
b- Isothermal
c- Isentropic
d- Isobaric
b- 82.2 oC
c- 38.1 oC
d- 68.6 oC
(21) What are the basic differences between spark ignition and Diesel engines ? Briefly explain
using sketches or diagrams if necessary.
(22) In air-conditioning cooling load calculations, there are internal and external sources of heat.
Name as many as you can and indicate whether the load is sensible, latent or both.
(23) Reheat in a gas turbine;
a- Increases thermal efficiency
b-180 o
c- 230 o
d- 270 o
University of Baghdad
College of Engr.
Mech. Engr. Dept.
Applied Mechanics
Time: 3 hrs.
a.
Only
if
it
is
at
b. Only if it is moving with constant
c. Only if it is moving with constant
d. If it is either at rest or moving with
velocity
e. If it is moving with either constant
or constant acceleration
a)
b)
c)
d)
25 N
40 N
50 N
None of the above
velocity
rest
velocity
velocity
constant
(-2i - 4j + 3k) m
(3i + 4j) m
(4j + 3k) m
(2i + 4j + 4k) m
None of the above
Fsin45(2m)
Fsin45(2m)
Fcos45(2m)
9.
Calculate
the
equivalent
single
resultant force and specify its x and y
coordinates.
Frz= ?
One answer only
a) 0
b) 100 N (down)
c) 200 N (down)
d) 400 N (down)
e) None of the above .
13. On a sheet of paper draw the freebody diagram of member BC, then
specify
the
single
equation
of
equilibrium that should be applied to
determine the resultant force acting at
the ends of the two-force member AB.
One answer only.
a)
b)
c)
d) None of the above
14. Which one of the following (a) Hook's law relates stress and strain.
statements concerning Hook's law is (b) Hook's law is valid only for springs.
false?
(c) Hook's haw can be verified
experimentally.
(d) Hook's law can be applied to a wide
range
of
materials.
(e) Hook's law is valid only within the
elastic limit of a given material.
15. The impact strength of a material is
an index of its:
( choose the correct answer )
a)
b)
c)
d)
e)
Toughness
Tensile strength
Capability of being cold worked
Hardness
Fatigue strength
(a) PlA/E
(b) Pl/AE
(c) E/PlA
(d) None of the above
(a) Fracture
(b) Fatigue
(c) Buckling
(d) Creep
pulley is ----------------------------------------------------------------------------Q2) detect the sentences if it is false or true and correct the false ones:
1- The conservation of linear momentum is
2- The mass moment of inertia can be found from the area of the body only.
3- In turning moment diagram for multi cylinder engine is the relation between
turning moment and crank angle.
4- In reciprocating masses the unbalanced force is balanced by additional mass in
the connecting rod .
5- The construction of cam profiles is drawn dependent on the forces that applied
on the cam by the follower.
Q3 ) ANSWER with equations only :1- For constant angular acceleration what are the angular velocity of a body after time t ?
2- If mass (m) falls from high (h) what is its velocity (v) ?
3- What is the couple effect on a vehicle turning around a curve?
Part C: Design ( 15 M )
1. Determine the force in member CB of the truss and indicate whether the members are in
tension or compression.
2. A 25 mm diameter bar is subjected to an axial load of 1000KN. Under the action of this load a
200 mm gauge length is found to extend 0.19 x 10-3 mm. Determine the modulus of elasticity for
the bar material.
3. What useful information is obtained from the tensile test of a ductile material?
4. Write the relations used for maximum stress when a machine member is subjected to tensile or
compressive stresses along with shearing stresses.
5. What is meant by endurance strength of a material? How do the size and surface condition of a
component and type of load affect such strength?
6. Distinguish between circumferential stress and longitudinal stress in a cylindrical shell, when
subjected to an internal pressure.
7. Discuss how the pipes are designed.
8. Show by neat sketches the various ways in which a riveted joint may fail.
9. What type of stresses are induced in shafts?
Part D: Vibrations ( 10 M )
Q1: Fill in the blanks using the words between brackets at the end of each sentence :
1: When the motion is repeated in equal intervals of time
repletion time
is called the
is ______.
as _______________.
3: In a viscously damped free vibration of a single degree of freedom spring-mass system , the
displacement x may by be found to be
is
______________ are possible. We refer to this case as _______________ when the damping term
is ___________ than
above equation within the parentheses are ___________. We refer to this case as _____________.
In the limiting case between the oscillatory and non oscillatory motion
, and the
. The magnitude of the impressed force is then nearly equal to the ____________. For
the phase angle is _______ and the inertia force, which is now __________, is balanced
Q2: determine the natural frequency of the mass M on the end of a cantilever beam of a neglegibel
mass shown in the figure. The deflection of the cantilever beam under a concentrated force P is
Q3: the logarithmic decrement is defined as the natural logarithm of the ratio of any successive
amplitudes. If the logarithmic decrement is 0.429:
a) Determine the ratio of any two successive amplitudes.
b) Show that the logarithmic decrement is also given by the equation
d) s1, 2 2.5 j
13
2
a)Z(t) = a(t)+b(t)-c(t)+d(t),
b) Z(t) = a(t)+b(t)+c(t)+d(t),
c) Z(t) = -(a(t)+c(t))+(b(t)+d(t)),
d) z(t) = -a(t)-b(t)-c(t)+d(t)
Q3) What are the time constants of the following transfer functions?
2
6
, G2 ( s)
G1 ( s)
0.5s 1
3s 2
a) 0.5,1.5 , b) 0.5,3 , c) 4,2 , d) 0.5,2
Q4) G1 (s) , G2 (s) and G3 ( s) have the same gain, but time constants of 3,4 and 5 seconds
respectively. Which responds more quickly to a step input?
a) They all respond the same since the gain is the same
b) G1 (s)
c) G2 (s)
d) G3 ( s)
Q5) What are the gain and natural frequency of the following system transfer function?
36
G ( s) 2
s 3s 36
a) 36,6
b) 6,6
c) 1,6 d) 6,1
Q6) The forward, feedback and closed loop transfer function for the system are:
30
30
3
30
a)
, 0,
b)
, 1,
2 s 31
2s 30
3s 1
2s 1
30
30
30
30
c)
, 1,
d)
, 0,
2s 31
2s 1
2s 1
2 s 31
Q8) If E ( s)
Q9) The percentage overshoot of a second order system to a step input depends only on:
a)The value of the step input
b)The value of the damping ratio
c)The value of the gain k
d)The parameter n
Q10) What are the pole (p) and zero (z) of the transfer function
s2
G (s)
s3
a) p=2, z=3
b)p=3, z=2
c)p=-2, z=-3
d)p=-3, z=-2
Q11) Draw the root locus plot and write the characteristic equations for the following
systems:
Q13) Draw the specification of transient response showing the tr , t s , t p ,p.o.s and ess .
Q14) Explain by drawing and write the formula for the gain margin and phase margin for
type one system third order differential equation.
11
University of Baghdad
College of Engr.
Mech. Engr. Dept.
Time: 3 hrs.
( 34 M )
d- 0.4 to 1 mm
c-mm/tooth
12- In order to check the clearance between two mating surfaces, a-------------gauge should be
used.
a-ring
b- plug
c- feeler
13- Which of the following materials has the greatest hot hardens?
a- Plain carbon steel
b-high speed steel
c-cemented carbides
14-Consider the following processes:
a-blending
b-Atomization
c-sintering
Which of the above processes is used for producing metal powder?
d-ceramics
d-comminuting
15-Why is aluminum and magnesium alloys not usually cast by centrifugal casting?
16- Why is it difficult to weld aluminum?
17- In casting, mold shift occurs due to ----------------------------.
18- Why does misrun occur?
19-what important property is an achieved by forging which is not obtainable by other
process?
20-For mild steel, the hot forging temperature range is:
a)
400 to 600 oc
b) 700 to 900 oc
c)1000 to 1200 oc
21) Extrusion force does not depend upon:
a-extrusion ratio b-type of extrusion process
d)1300 to 1500 oc
d-working temp.
6280 W
b) 628 W
c)314 W
( 34 M )
14.
15.
16.
17.
18.
19.
20.
21.
22.
23.
24.
25.
26.
27.
28.
29.
30.
There must always be enough space for the movement of the worker and machines to be
operated, on the floor of the factory?
Machines must be set before starting the inspection of produced parts.
The number of operations for a product will determine the size of the plant?
It is always possible to use measuring devices in the measurements of tolerances of
operations.
The use of activity chart will determine the sequence of operations for a product?
Quality control charts will always define the tolerances of the parts.
There is no limitation on price increase when reducing the economic batch quantity?
In control charts, when the lower bound is negative, it must be set equal to zero.
The process used for the manufacturing of the parts limits material utilization?
Double sampling plan is used when the tolerances are high.
Mass production is not considered as a flexible manufacturing system?
The number of defected parts in an operation is affected by the accuracy of the machine
used.
A non-promising activity can be made profitable by reducing its consumption of the
limited resources?
In control charts, the batch size must be constant over all stages of production.
The bottlenecked machine controls the maximum output of a line?
The number of finished parts returned from customers as defects measures quality.
The size of the batch is affected by the changes made in the tools?
( 34 M )
C HCP
C Has no effect
C Both A & B
C 13 %
C Both A&B
C Both A & B
C Both A & B