← MES Jr. Grade
Past Questions — 2015
Lancashire boiler is a
A)
stationary fire tube boiler
B)
stationary water tube boiler
C)
water tube boiler with natural circulation
D)
mobile fire tube boiler
A Lancashire boiler is a stationary, fire-tube, internally fired boiler. The hot flue gases pass through tubes surrounded by water, which is the defining feature of a fire-tube boiler. It is not a water-tube boiler, and it is not mobile.
A fusible plug is fitted in small boiler in order to
A)
avoid excessive build up of pressure
B)
avoid explosion
C)
extinguish fire if water level in the boiler falls below alarming limit
D)
control steam dome
A fusible plug is a safety device fitted in a boiler crown. If the water level drops too low, the plug gets overheated, the fusible metal melts, and steam/water is released onto the fire. This extinguishes the fire and prevents overheating of the boiler shell. It is not primarily for pressure control or steam dome control.
The efficiency of a centrifugal pump is maximum when blades are
A)
straight
B)
bent forward
C)
bent backward
D)
bent backward first and then bent forward
In a centrifugal pump, backward-curved (backward bent) blades give the highest efficiency because they reduce shock losses, provide stable operation, and allow a smooth transfer of energy to the fluid. Forward-curved blades may give higher discharge but are less efficient and less stable, while straight blades are not as efficient as backward-curved ones. Hence, maximum efficiency is obtained with backward bent blades.
The compression ratios for diesel engines lie in the range of
A)
5 to 8
B)
3 to 6
C)
6 to 10
D)
15 to 20
Diesel engines operate on compression ignition, so they need a much higher compression ratio than petrol engines to raise the air temperature enough for fuel ignition. Typical diesel engine compression ratios are in the range of about 15:1 to 20:1. The lower ranges given in options (a), (b), and (c) are more characteristic of petrol engines or are too low for diesel engines.
A fluid is a substance that
A)
is essentially incompressible
B)
has a viscosity that always decreases with temperature
C)
cannot remain at rest when subjected to a shearing stress
D)
cannot be subjected to shear forces
A fluid is defined as a substance that deforms continuously under any applied shear stress. In other words, it cannot sustain shear stress in static equilibrium and therefore cannot remain at rest when subjected to a shearing stress. Option (a) is false because fluids may be compressible or incompressible. Option (b) is false because viscosity does not always decrease with temperature for all fluids. Option (d) is incorrect because fluids can be subjected to shear forces; they simply keep deforming under them.
A thermodynamic process, in which no heat is supplied or rejected and entropy is not constant, is called
A)
isentropic
B)
isothermal
C)
polytropic
D)
adiabatic
A process in which no heat is supplied to or rejected from the system is called an adiabatic process. If such a process is also reversible, then entropy remains constant and it is called isentropic. Here entropy is not constant, so it is adiabatic but not isentropic. Isothermal means constant temperature, and polytropic is a broader process relation.
Which of the following does not relate to C.I. engine?
A)
fuel pump
B)
fuel injector
C)
governor
D)
carburettor
A C.I. (Compression Ignition) engine is a diesel engine. It uses a fuel pump, fuel injector, and governor. A carburettor is used in S.I. (Spark Ignition) engines to mix air and fuel before combustion, so it does not relate to a C.I. engine.
Which of the following rotary types is a positive displacement compressor?
A)
radial flow turbo compressor
B)
axial flow turbo compressor
C)
screw type compressor
D)
mixed flow compressor
A positive displacement compressor traps a fixed volume of air and then reduces its volume to increase pressure. A screw type compressor is a rotary positive displacement compressor because air is compressed between rotating helical screws. In contrast, radial flow turbo, axial flow turbo, and mixed flow compressors are dynamic compressors, not positive displacement types.
In a vapour compression cycle, the refrigerant immediately after expansion valve is
A)
liquid
B)
dry vapour
C)
saturated liquid
D)
wet vapour
In a vapour compression refrigeration cycle, the expansion valve causes a sudden drop in pressure. This throttling process converts the high-pressure liquid refrigerant into a low-pressure mixture of liquid and vapour, called wet vapour or a wet mixture. Therefore, immediately after the expansion valve, the refrigerant is wet vapour. The other options are incorrect because it is not fully liquid, not dry vapour, and not saturated liquid after expansion.
Bernoulli’s theorem deals with the law of conservation of
A)
mass
B)
energy
C)
momentum
D)
none of these
Bernoulli’s theorem states that for an ideal fluid flowing steadily, the sum of pressure energy, kinetic energy, and potential energy remains constant along a streamline. Therefore, it is based on the law of conservation of energy. Mass is conserved by the continuity equation, and momentum is related to Newton’s second law, not Bernoulli’s theorem.
The ideal efficiency of a simple gas turbine depends upon
A)
temperature ratio
B)
pressure ratio
C)
volume ratio
D)
mass ratio
For an ideal simple gas turbine (Brayton cycle), thermal efficiency depends primarily on the pressure ratio. In the ideal cycle, higher pressure ratio generally improves efficiency up to a limit. Temperature ratio is not the direct controlling parameter in the standard expression for simple gas turbine efficiency. Volume ratio and mass ratio are not the governing factors for ideal cycle efficiency.
Practically all the engineering processes are
A)
quasi-static
B)
reversible
C)
irreversible
D)
thermodynamically equilibrium
In real engineering practice, processes occur with friction, heat loss, unrestrained expansion, finite temperature differences, and other dissipative effects. Because of these irreversibilities, practically all engineering processes are irreversible.
Why others are incorrect:
- (a) Quasi-static processes are idealized and occur infinitely slowly; real processes are not practically quasi-static.
- (b) Reversible processes are ideal limits and cannot be achieved in practice.
- (d) Thermodynamic equilibrium describes a state, not the general nature of real engineering processes.
The basic job of feed water treatment in boilers is to overcome the problem of
A)
corrosion
B)
scaling
C)
carry over
D)
all of these
Feed water treatment in boilers is done to remove dissolved salts, gases, and suspended impurities. This helps prevent: corrosion caused by dissolved oxygen and carbon dioxide, scaling caused by hardness salts, and carry over due to foaming and impurities in boiler water. Therefore, the basic job of feed water treatment is to overcome all these problems.
A heat engine is supplied heat at the rate of 15000 N m/s and gives an output of 4500 W. The thermal efficiency is
A)
45%
B)
50%
C)
30%
D)
33%
Thermal efficiency of a heat engine is given by: efficiency = output work / heat input. Here, heat supplied = 15000 N m/s = 15000 W and output = 4500 W. So, efficiency = 4500 / 15000 = 0.3 = 30%. Therefore, the correct option is (c). Option (a) 45%, (b) 50%, and (d) 33% are all incorrect because they do not match the ratio of output to input.
During adiabatic saturation process on unsaturated air, the parameter which remains constant is
A)
dry bulb temperature
B)
dew point temperature
C)
wet bulb temperature
D)
relative humidity
In an adiabatic saturation process, unsaturated air is brought into contact with water without heat exchange with the surroundings. The process continues until the air becomes saturated, and the temperature that remains constant throughout this idealized process is the wet bulb temperature. Dry bulb temperature changes due to evaporation, dew point temperature is not constant in the process, and relative humidity increases as saturation is approached.
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 body submerged in a fluid, the dominant force ratio is between inertial and viscous forces. To ensure dynamic similarity between model and prototype, the Reynolds number must be the same in both. Weber number is used when surface tension effects are important, Froude number for gravity-dominated free-surface flows, and Mach number for compressible flows.
When a mixture of air and water vapour is cooled at constant pressure up to the saturation temperature of water vapour, this temperature is called
A)
wet bulb temperature
B)
dew point temperature
C)
dry bulb temperature
D)
adiabatically saturated temperature
When moist air is cooled at constant pressure, the temperature at which the water vapour just begins to condense is called the dew point temperature. It is the saturation temperature corresponding to the existing partial pressure of water vapour.
Why others are incorrect:
- (a) Wet bulb temperature: related to evaporative cooling, not the temperature at which vapour starts condensing.
- (c) Dry bulb temperature: the actual air temperature measured by a normal thermometer.
- (d) Adiabatically saturated temperature: temperature reached by air-vapour mixture after adiabatic saturation, different from dew point.
The ratio of Cp to Cv of a perfect gas is called
A)
isothermal index
B)
adiabatic index
C)
ideal gas index
D)
isentropic index
For a perfect gas, the ratio Cp/Cv is denoted by γ (gamma). This ratio is called the adiabatic index, because it appears in adiabatic relations for gases. The other options are not the standard term used for Cp/Cv.
A floating body is said to be in a state of stable equilibrium
A)
when its metacentric height is zero
B)
when the metacentre is above the centre of gravity
C)
when the metacentre is below the centre of gravity
D)
only when the centre of gravity is below its centre of buoyancy
For a floating body, stability depends on the relative positions of the metacentre (M) and centre of gravity (G). If M is above G, the metacentric height is positive, so after a small tilt the restoring couple brings the body back to its original position. Hence the body is in stable equilibrium. If M and G coincide, equilibrium is neutral. If M is below G, the body is unstable. Therefore, option (b) is correct.
Rotameter is used to measure
A)
fluid pressure
B)
flow rate
C)
velocity
D)
viscosity
A rotameter is a variable-area flow meter used to measure the flow rate of liquids or gases. As the fluid passes upward through a tapered tube, the float rises until forces balance; the float position indicates the discharge. It does not measure pressure, velocity directly, or viscosity.
The device which delivers the heat from low temperature to high temperature in a cyclic process is known as
A)
heat engine
B)
heat pump
C)
compressor
D)
condenser
A device that transfers heat from a low-temperature region to a high-temperature region in a cyclic process is called a heat pump. It works by consuming work input to move heat against the natural direction of flow. A heat engine does the opposite: it converts heat into work. A compressor is only a component used in refrigeration systems, and a condenser is the part where refrigerant rejects heat.
Axial flow pump is started with its delivery valve
A)
kept fully closed
B)
kept fully open
C)
irrespective of any position
D)
none of these
An axial flow pump should be started with its delivery valve fully open. Since the pump handles a very large discharge at low head, starting against a closed delivery valve can cause unnecessary load and poor operating conditions. In contrast, keeping the valve open allows smooth starting and normal flow development. Hence, option (b) is correct. Option (a) is incorrect because a closed valve is not suitable for starting. Option (c) is wrong because the valve position does matter. Option (d) is incorrect.
Which of the following computer memories is fastest?
A)
cache
B)
primary
C)
mass storage
D)
backup memories
Cache memory is the fastest among the given options because it is located very close to the CPU and stores frequently used data/instructions for quick access. Primary memory (RAM) is slower than cache, while mass storage (like HDD/SSD) and backup memories are much slower than both.
Define VSWR in a transmission line.
Which of the following is not a negative resistance device?
A)
Gunn diode
B)
Tunnel diode
C)
Impatt diode
D)
Varactor diode
A negative resistance device exhibits a region where an increase in voltage causes a decrease in current. Gunn diode, tunnel diode, and IMPATT diode are all used as negative resistance devices in microwave circuits. A varactor diode, however, is a voltage-controlled variable capacitor used for tuning, not a negative resistance device.