← MES Jr. Grade
Past Questions
The number of power strokes per minute in a two-stroke engine is
A)
equal to the rpm
B)
half of the rpm
C)
twice of the rpm
D)
four times of the rpm
In a two-stroke engine, one power stroke occurs in every revolution of the crankshaft. Therefore, the number of power strokes per minute is equal to the engine speed in rpm. In a four-stroke engine, it would be half the rpm because one power stroke occurs every two revolutions.
The thermal property that remains same on the two sides of the impulse wheel of a steam turbine is
A)
heat
B)
temperature
C)
velocity
D)
pressure
In an impulse turbine, the entire pressure drop of steam occurs in the nozzle, not in the moving blades (impulse wheel). Therefore, across the two sides of the impulse wheel, the pressure remains essentially the same. The steam’s velocity changes as it passes over the blades, but pressure does not. Hence, the correct answer is pressure.
A high specific speed Francis turbine is
A)
axial flow turbine
B)
tangential flow turbine
C)
mixed flow turbine
D)
radial flow turbine
A Francis turbine is a reaction turbine in which water enters radially inward and leaves axially, so it is a mixed flow turbine. In general, Francis turbines are classified as mixed flow turbines, while Pelton turbines are tangential flow turbines and Kaplan turbines are axial flow turbines. Hence, the correct answer is mixed flow turbine.
The compression ratio of Diesel engine may have the range of
A)
8 to 10
B)
10 to 15
C)
16 to 20
D)
none of these
A Diesel engine works on compression ignition, so it requires a much higher compression ratio than a petrol engine. Typical Diesel engine compression ratios are in the range of about 16:1 to 20:1. Option (a) 8 to 10 is too low and is more typical of petrol engines. Option (b) 10 to 15 is still generally below the usual Diesel range. Therefore, the correct answer is (c) 16 to 20.
A venturimeter is used for measuring
A)
pressure
B)
flow rate
C)
total energy
D)
piezometric head
A venturimeter is a differential pressure device used to measure the discharge or flow rate of a fluid flowing through a pipe. It works on Bernoulli’s principle: as fluid passes through the constricted throat, velocity increases and pressure decreases, and this pressure difference is used to calculate flow rate. It does not directly measure pressure, total energy, or piezometric head.
Bernoulli equation is applicable for
A)
steady rotational flow
B)
steady rotational compressible flow
C)
steady irrotational incompressible flow
D)
unsteady irrotational incompressible flow
Bernoulli’s equation is derived for an ideal fluid flow and is applicable along a streamline. In its common engineering form, it is used for steady, incompressible flow; when the flow is also irrotational, the Bernoulli constant is the same throughout the flow field. Hence, the correct option is steady irrotational incompressible flow. The other options are incorrect because Bernoulli’s equation does not generally apply to rotational flow, compressible flow in this basic form, or unsteady flow without modification.
For high head and low discharge, the hydraulic machinery selected is
A)
Francis turbine
B)
Kaplan turbine
C)
Pelton turbine
D)
none of these
For a high head and low discharge condition, an impulse turbine is preferred. The Pelton turbine is specifically designed for high head, low flow rate applications. Francis turbine is used for medium head and medium discharge, while Kaplan turbine is used for low head and high discharge. Therefore, the correct answer is Pelton turbine.
An isentropic process is always
A)
irreversible and adiabatic
B)
reversible and isothermal
C)
reversible and adiabatic
D)
frictionless and irreversible
An isentropic process is one in which entropy remains constant. For a process to be isentropic, it must be both adiabatic (no heat transfer) and reversible (no entropy generation). Hence, the correct answer is reversible and adiabatic. The other options are incorrect because irreversible processes generate entropy, and isothermal means constant temperature, not constant entropy.
If the boundary of a thermodynamic system is impervious to the flow of matter, it is called
A)
open system
B)
closed system
C)
isolated system
D)
adiabatic system
A boundary that is impervious to the flow of matter means no mass can enter or leave the system. Such a system is called a closed system. An open system allows both mass and energy transfer, while an isolated system allows neither mass nor energy transfer. An adiabatic system refers to no heat transfer, not necessarily no mass transfer.
Reciprocating pumps are suitable for
A)
high pressure
B)
low pressure
C)
moderate pressure
D)
high volume
Reciprocating pumps are positive displacement pumps. They deliver a small discharge at very high pressure, so they are suitable for high-pressure, low-flow applications. They are not preferred for high volume because their discharge is pulsating and limited compared to centrifugal pumps. Hence, the correct answer is high pressure.
The wave length of radiation emitted by a body depends upon the surface
A)
nature
B)
area
C)
temperature
D)
roughness
The wavelength of radiation emitted by a body is governed by its temperature, according to Wien’s displacement law: higher temperature means shorter peak wavelength. It does not depend on surface area, and while surface nature/roughness can affect emissivity, the characteristic wavelength of emitted radiation is primarily determined by temperature. Hence, the correct option is (c) temperature.
Pelton turbine is a
A)
Reaction turbine
B)
Impulse turbine
C)
Radial flow turbine
D)
Axial flow turbine
A Pelton turbine works on the impulse principle: a high-velocity jet of water strikes the buckets and transfers momentum, while the pressure over the runner remains essentially atmospheric. Therefore, it is an impulse turbine. It is not a reaction turbine, and it is neither radial flow nor axial flow.
In fluid modeling of flow pattern around a body submerged in a fluid, the non-dimensional number that has to be kept the same in the model and prototype is
A)
Weber number
B)
Froude number
C)
Mach number
D)
Reynolds number
For flow pattern around a submerged body in fluid modeling, the dominant force balance is between inertial and viscous forces. Dynamic similarity is therefore achieved by keeping the Reynolds number the same in the model and prototype. Weber number is important when surface tension effects dominate, Froude number is used for gravity-dominated free-surface flows, and Mach number is relevant for compressible flows.
For a given pressure and temperature of steam, the thermal efficiency of the steam engine with condenser compared to a steam engine without condenser is always
A)
lower
B)
higher
C)
same
D)
none of these
A steam engine with a condenser operates at a lower exhaust pressure, so the steam expands through a larger pressure ratio and does more work. For the same initial steam pressure and temperature, this increases the cycle efficiency. A non-condensing engine exhausts to atmospheric pressure, so it has less expansion and lower thermal efficiency. Therefore, the efficiency is always higher with a condenser.
The loss of head due to friction in a pipe of uniform diameter in which a viscous flow is taking place is given in terms of Reynolds number (R) as
A)
16/R
B)
64/R
C)
4/R
D)
1/R
For viscous (laminar) flow in a circular pipe of uniform diameter, the Darcy–Weisbach friction factor is f = 64/R, where R is the Reynolds number. The head loss due to friction is therefore expressed using this relation. Hence, the correct option is (b) 64/R. The other options do not match the standard laminar-flow pipe friction formula.
The internal energy of a perfect gas depends on
A)
temperature and pressure
B)
only temperature
C)
temperature and entropy
D)
temperature and enthalpy
For a perfect gas (ideal gas), internal energy is a function of temperature only. This is because the internal energy depends on molecular kinetic energy, which changes with temperature, and not directly on pressure, entropy, or enthalpy. Hence option (b) is correct. The other options are incorrect because pressure, entropy, and enthalpy are not the sole determining variables for the internal energy of a perfect gas.
Kinematic similarity between model and prototype is the
A)
similarity of discharge
B)
similarity of shape
C)
similarity of streamline pattern
D)
none of these
Kinematic similarity means the model and prototype have the same motion characteristics, i.e., the flow pattern is similar. This is expressed by similarity of streamline pattern and velocity ratios at corresponding points.
- (a) Similarity of discharge is not kinematic similarity; discharge depends on scale and velocity.
- (b) Similarity of shape is geometric similarity, not kinematic similarity.
- (c) Similarity of streamline pattern is correct because it describes identical flow motion.
- (d) Incorrect since option (c) is correct.
The fluid forces considered in the derivation of Navier Stokes equation are
A)
gravity, pressure and viscous
B)
gravity, pressure and turbulent
C)
pressure, viscous and turbulent
D)
gravity, viscous and turbulent
The Navier–Stokes equation is derived by applying Newton’s second law to a fluid element and accounting for the main forces acting on it: body force due to gravity, surface force due to pressure, and viscous force due to fluid friction. Turbulent force is not included in the basic derivation of the Navier–Stokes equation.
In case of S.I. engine, to have best thermal efficiency the fuel-air mixture ratio should be
A)
rich
B)
lean
C)
may be rich or lean
D)
same
In a spark-ignition (S.I.) engine, best thermal efficiency is generally obtained with a slightly lean fuel-air mixture. A lean mixture contains excess air, which promotes more complete combustion and reduces fuel wastage, improving efficiency. A rich mixture is used when more power is needed, but it lowers thermal efficiency because of incomplete combustion and higher fuel consumption. Therefore, the correct answer is lean.
Octane number rating is used to determine the ignition quality of fuels for
A)
C.I. engine
B)
S.I. engine
C)
Hydrogen engine
D)
Steam engine
Octane number measures the anti-knock quality of a fuel, i.e., its resistance to premature ignition or knocking. This is used for spark-ignition (S.I.) engines, where the fuel-air mixture is ignited by a spark plug. In contrast, diesel engines (C.I. engines) are rated by cetane number, which indicates ignition quality under compression. Hydrogen and steam engines are not the standard context for octane rating.
Which one of the following components is not a boiler accessory?
A)
injector
B)
superheater
C)
feed pump
D)
safety valve
Boiler accessories are devices fitted to improve the efficiency and performance of a boiler, such as an injector, superheater, and feed pump. A safety valve, however, is a boiler mountings item used for safety to release excess pressure and prevent explosion. Therefore, it is not a boiler accessory.
In parallel flow heat exchangers, the two fluids i.e. hot and cold travel in the
A)
same direction
B)
opposite direction
C)
cross direction
D)
axial direction
In a parallel flow heat exchanger, the hot and cold fluids enter from the same end and move in the same direction. Hence, the correct answer is (a) same direction. Option (b) describes counter-flow, and (c) describes cross-flow. Option (d) is not a standard classification of heat exchanger flow arrangement.
Stefan Boltzmann law is applicable for heat transfer by
A)
conduction
B)
convection
C)
radiation
D)
conduction and radiation combination
Stefan–Boltzmann law states that the total radiant heat emitted by a black body is proportional to the fourth power of its absolute temperature. Therefore, it applies to heat transfer by radiation. It is not used for conduction or convection, which follow different heat transfer mechanisms and laws.
Thermal diffusivity is
A)
a physical property of the material
B)
function of temperature
C)
a dimensionless parameter
D)
useful in case of radative heat transfer
Thermal diffusivity is a material property defined as α = k / (ρc_p), where k is thermal conductivity, ρ is density, and c_p is specific heat. It indicates how quickly heat spreads through a material. It is not dimensionless, and while it may vary with temperature for some materials, its basic classification is as a physical property of the material. Hence, option (a) is correct.
The location of the center of pressure over a surface immersed in a liquid is
A)
always above the centroid
B)
will be at the centroid
C)
will be below the centroid
D)
depends upon the density of fluid
For a plane surface immersed in a liquid, hydrostatic pressure increases with depth. Because the lower portions of the surface experience greater pressure than the upper portions, the resultant force acts at a point deeper than the centroid. Hence, the center of pressure lies below the centroid. It is not at the centroid except in special cases like a horizontal surface, and it does not depend on fluid density for its relative position.