MES Jr. Grade • Paper-I
Cavitation is caused by
A)
high velocity
B)
low pressure
C)
weak material
D)
high pressure
Option B: low pressure. This matches the standard definition or established fact for the concept asked.
MES Jr. Grade • Paper-I
Which factor is considered while selecting the diameter of piston rod in hydraulic cylinder?
A)
bore diameter
B)
length of stroke
C)
load
D)
all of these
Option D: all of these. This matches the standard definition or established fact for the concept asked.
MES Jr. Grade • Paper-I
For a hypersonic flow, the mach number is
A)
unity
B)
greater than unity
C)
greater than 2
D)
greater than 4
Option D: greater than 4. The result follows from the standard engineering relationship for the stated conditions.
MES Jr. Grade • Paper-I
In counter flow heat exchangers
A)
both the fluids at inlet (of heat exchanger where hot fluid enters) are in their coldest state
B)
both the fluids at inlet are in their hottest state
C)
both the fluids at exit are in their hottest state
D)
one fluid is in hottest state and other in coldest state at inlet
Option D: one fluid is in hottest state and other in coldest state at inlet. The result follows from the standard engineering relationship for the stated conditions.
MES Jr. Grade • Paper-I
A counter flow shell and tube heat exchanger is used to heat water with hot exhaust gases. The water (c=4180 J/kgK) flows at the rate of 2 kg/s and the exhaust gases (c=1000 J/kgK) flow at the rate of 5 kg/s. If the heat transfer surface area is 32 m2 and the overall heat transfer coefficient is 200 W/m2K. The NTU of the heat exchanger is
A)
4.5
B)
2.4
C)
8.6
D)
1.28
NTU=UA/Cmin=(200×32)/(5×1000)=1.28.
MES Jr. Grade • Paper-I
A plane wall is 25 cm thick with an area of 1 m2, and has a thermal conductivity of 0.5 W/mK. If a temperature difference of 60°C is imposed across it, what is the heat flow?
A)
180 W
B)
140 W
C)
120 W
D)
160 W
Q=kAΔT/L=0.5×1×60/0.25=120 W.
MES Jr. Grade • Paper-I
A wall of thickness 0.6 m has width and has a normal area 1.5 m2 and is made up of material of thermal conductivity 0.4 W/mK. The temperatures on the two sides are 800°C. What is the thermal resistance of the wall?
A)
2 K/W
B)
3.5 K/W
C)
1 K/W
D)
2.3 K/W
Thermal resistance R=L/(kA)=0.6/(0.4×1.5)=1 K/W.
MES Jr. Grade • Paper-I
Low-torque high-speed motors are used in
A)
cranes
B)
winches
C)
fans
D)
all of these
Option C: fans. The result follows from the standard engineering relationship for the stated conditions.
MES Jr. Grade • Paper-I
What causes suction of fluid into the gear pump?
A)
when pressure drops during disengagement of teeth at the suction side
B)
when pressure increases during disengagement of teeth at the suction side
C)
when pressure drops during engagement of teeth at the suction side
D)
when pressure increases during engagement of teeth at the suction side
Option A: when pressure drops during disengagement of teeth at the suction side. This matches the standard definition or established fact for the concept asked.
MES Jr. Grade • Paper-I
The time required to close a valve gradually is (where L is the length of pipe and C = velocity of pressure wave)
A)
2L/C
B)
≥ 2L/C
C)
> 2L/C
D)
> 4L/C
For gradual valve closure, the closure time must be at least the pressure-wave travel round-trip time 2L/C to avoid water hammer.
MES Jr. Grade • Paper-I
For a fully developed laminar flow through a pipe with uniform wall temperature, the heat transfer coefficient is
A)
not directly proportional to the thermal conductivity of fluid film
B)
inversely proportional to the pipe diameter
C)
dependent on fluid velocity
D)
dependent on fluid viscosity
Option C: dependent on fluid velocity. The result follows from the standard engineering relationship for the stated conditions.
MES Jr. Grade • Paper-I
A composite wall has two layers of different materials having thermal conductivities of k1 and k2. If each layer has the same thickness, the equivalent thermal conductivity of the wall is
A)
(k1 + k2) / (k1 + k2)
B)
k1 k2 / (k1 + k2)
C)
2k1 k2 / (k1 + k2)
D)
(k1 + k2) / 2
For equal thickness layers in series, keq=2k1k2/(k1+k2).
MES Jr. Grade • Paper-I
If jet of water coming out from a nozzle with a velocity of 9.81 m/s, the angle of elevation being 30°, the time to reach the highest point is
A)
0.25 sec
B)
0.50 sec
C)
1.0 sec
D)
1.5 sec
The initial vertical velocity is 9.81 sin30°=4.905 m/s; time to highest point is 4.905/9.81=0.5 s.
MES Jr. Grade • Paper-I
Upto the critical radius of insulation
A)
Added insulation will increase heat loss
B)
Added insulation will decrease heat loss
C)
Convective heat loss will be less than conductive heat loss
D)
Heat flux will decrease
Below the critical radius of insulation, adding insulation can initially increase heat loss because the surface-area effect outweighs the added conduction resistance.
MES Jr. Grade • Paper-I
In MLTu system, the dimension of thermal conductivity is
A)
ML-1T-1θ-1
B)
MLT-1θ-1
C)
MLT-3θ-1
D)
MLT-2θ-1
Thermal conductivity has dimensions of power/(length×temperature) = MLT⁻³Θ⁻¹.
MES Jr. Grade • Paper-I
If R is the Renold’s number, the coefficient of friction for laminar flow is
A)
16/Re
B)
64/Re
C)
12/Re
D)
8/Re
For laminar pipe flow, the Darcy friction factor is 64/Re; the Fanning friction factor is 16/Re. The question's convention gives option A.
MES Jr. Grade • Paper-I
The value of Prandtl number for air is about
A)
0.1
B)
0.3
C)
0.7
D)
1.7
Air has a Prandtl number of about 0.7 under ordinary conditions.
MES Jr. Grade • Paper-I
The total energy developed by the hydraulic oil in a system is given as
A)
Total energy = (Potential energy + Pressure energy)
B)
Total energy = (Potential energy + Kinetic energy)
C)
Total energy = (Potential energy – Kinetic energy)
D)
none of these
Option D: none of these. This matches the standard definition or established fact for the concept asked.
MES Jr. Grade • Paper-I
The property of stream function ψ is :
A)
ψ is constant everywhere on any stream line
B)
the flow around any path in the fluid is zero for continuous flow
C)
the velocity vector may be found by differentiating the stream function
D)
all of these
Option D: all of these. This matches the standard definition or established fact for the concept asked.
MES Jr. Grade • Paper-I
The total energy developed by the hydraulic oil in a system is given as
A)
Total energy = (Potential energy + Pressure energy)
B)
Total energy = (Potential energy + Kinetic energy)
C)
Total energy = (Potential energy – Kinetic energy)
D)
None of these
Based on established principles in Mechanical Engineering, the correct and most appropriate choice is 'None of these' (Option D).
MES Jr. Grade • Paper-I
LMTD in case of counter flow heat exchanger as compared to parallel flow heat exchanger is
A)
Higher
B)
Lower
C)
Same
D)
Depends on the area of heat exchanger
Based on established principles in Mechanical Engineering, the correct and most appropriate choice is 'Same' (Option C).
MES Jr. Grade • Paper-I
The time required to close a valve gradually is (where L is the length of pipe and C = velocity of pressure wave)
A)
2L/C
B)
≥ 2L/C
C)
> 2L/C
D)
> 4L/C
Based on established principles in Mechanical Engineering, the correct and most appropriate choice is '≥ 2L/C' (Option B).
MES Jr. Grade • Paper-I
The product of Reynolds number and Prandtl number is known as
A)
Stanton number
B)
Biot number
C)
Peclet number
D)
Grashoff number
Based on established principles in Mechanical Engineering, the correct and most appropriate choice is 'Biot number' (Option B).
MES Jr. Grade • Paper-I
An object having 10 kg mass weighs 9.81 kg on a spring balance. The value of ‘g’ at this place is
A)
10 m/sec 2
B)
9.81 m/sec 2
C)
10.2 m/sec 2
D)
9 m/sec 2
Based on established principles in the relevant subject area, the correct and most appropriate choice is '9.81 m/sec 2' (Option B).
MES Jr. Grade • Paper-I
The temperature range for transition boiling is:
A)
30°C ≤ ΔTe ≤ 150°C
B)
5°C ≤ ΔTe ≤ 30°C
C)
30°C ≤ ΔTe ≤ 120°C
D)
ΔTe ≥ 150°C
Based on established principles in Mechanical Engineering, the correct and most appropriate choice is '30°C ≤ ΔTe ≤ 150°C' (Option A).
