# Quiz: Mechanical Engineering 23 April 2021

Quiz: Mechanical Engineering
Exam: AE/JE
Topic: Miscellaneous

Each question carries 2 mark
Negative marking: 1/3 mark
Time: 10 Minutes

Q1. Which one of the following thermodynamic processes approximates the steaming of food in a pressure cooker?
(a) isenthalpic
(b) isobaric
(c) isochoric
(d) isothermal

Q2. A closed system undergoes a process 1-2 for which the values of Q(1-2) and W(1-2) are + 20kJ and + 50kJ, respectively. If the system is returned to state 1 and Q(2-1) is –10kJ, what is the value of the work W(2-1) ?
(a) +20 kJ
(b) -40 kJ
(c) -80 kJ
(d) +40 kJ

Q3. An oil of specific gravity 0.9 has viscosity of 0.28 stokes at 38°C. What will be its viscosity in Ns/m²?
(a) 0.2520
(b) 0.0311
(c) 0.0252
(d) 0.0206

Q4. In reaction turbines, the draft tube is used
(a) for the safety of the turbine
(b) to convert the kinetic energy of flow by a gradual expansion of the flow cross-section
(c) to destroy the undesirable eddies
(d) for none of the above purposes

Q5. Which one of the following is measured by a rotameter?
(a) Velocity of fluids
(b) Discharge of fluids
(c) Viscosity of fluids
(d) Rotational speed of solid shafts

Q6. Fraction of radiative energy leaving one surface that strikes the other surface is called
(a) Radiative flux
(b) Emissive power of the first surface
(c) View factor
(d) Reradiation flux

Q7. The fouling factor in heat exchanger is defined as
(a) Rf=Udirty-Uclean
(b) Rf=1/Udirty -1/Uclean
(c) 1/Rf =1/Udirty -1/Uclean
(d) 1/Rf =Udirty-Uclean

Q8. In a boiler, the air preheater is invariably located between:
(a) Forced draft fan and chimney
(b) Forced draft fan and furnace
(c) Economizer and feed pump
(d) Condenser and feed pump

Q9. What is an azeotrope?
(a) A non-halogenic refrigerant
(b) A refrigerant dissolved in alcohol
(c) A mixture of refrigerants without phase separation
(d) An eco-friendly refrigerant

Q10. Piston compression rings are made of which one of the following?
(a) Cast iron
(b) Bronze
(c) Aluminium
(d) White metal

Solutions

S1. Ans.(c)
Sol. Volume of pressure cooker is always constant. Hence, it is isochoric process.

S2. Ans.(b)
Sol. For process 1 -2
U1+Q=U2+W
U1-U2=W-Q=50-20=30 kJ
For process 2 – 1
U2+Q=U1+W
Q+U2-U1=W
-10-30=W
W=-40 kJ

S3. Ans (c)
Sol. Dynamic viscosity,
μ=ρυ=(0.9×1000)×(0.28×10^(-4) )
=0.0252 Ns/m²

S4. Ans (b)
Sol. The draft tube has two purposes as follows:
It permits a negative or suction head to be established at the runner exist, thus making it possible to install the turbine above the tail race level without loss of head.
It converts a large proportion of velocity energy rejected from the runner into useful pressure energy. i.e. acts as a recuperator of pressure energy.

S5. Ans.(b)
Sol. Rotameter and elbow meter measure discharge through pipes.

S6. Ans (c)
Sol. The view factor is the fraction of radiative energy that diffused from one surface element and strikes the other surface directly.

S7. Ans (b)
Sol. The resistance due to fouling = Rf
∴1/Udirty =1/Uclean +1/(1/Rf )
∴ Rf=1/Udirty -1/Uclean

S8. Ans (b)
Sol. In a boiler, the air preheater is invariably located between Forced draft fan and furnace
S9. Ans.(c)
Sol. Azeotrope is a mixture of refrigerants without phase separation.

S10. Ans.(a)
Sol. Since grey cast iron has properties of self-lubrication and damping of small vibrations, they are widely used for machine base, engine frames, drainage pipes, elevator and industrial furnace counter weights, pump housings cylinder and piston rings of IC engines, flywheel etc.

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