← MES Jr. Grade
Past Questions
Thermal power plant works on
A)
Carnot cycle
B)
Joule cycle
C)
Rankine Cycle
D)
Otto cycle
A thermal power plant (steam power plant) generates electricity by producing steam in a boiler, expanding it through a turbine, condensing it, and pumping it back. This sequence is the Rankine cycle. Carnot cycle is an ideal theoretical cycle, Joule cycle is used for gas turbines, and Otto cycle is used in petrol engines.
Which of the following thermodynamic properties is not an example of point function?
A)
volume
B)
temperature
C)
pressure
D)
work
A point function depends only on the state of the system and not on the path taken. Volume, temperature, and pressure are state functions, so they are point functions. Work depends on the path followed during a process, so it is a path function, not a point function.
The refrigerant used in vapour absorption refrigerator is
A)
freon-12
B)
ammonia
C)
aqua-ammonia
D)
carbon di-oxide
In a vapour absorption refrigerator, the working pair is commonly ammonia as the refrigerant and water as the absorbent, together called aqua-ammonia. Hence, aqua-ammonia is the correct answer. Freon-12 is mainly used in vapour compression systems, and carbon dioxide is not the standard refrigerant for vapour absorption refrigerators in such exam context.
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.
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.
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.
To produce high head by multi-stage centrifugal pumps, the impellers are connected in
A)
series
B)
parallel
C)
series and parallel
D)
none of these
In multi-stage centrifugal pumps, impellers are connected in series to increase the pressure head. The discharge from one impeller enters the next, so the heads developed by each stage add up. Parallel connection is used to increase discharge, not head. Hence, the correct answer is series.
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 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.
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 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.
An enclosure is formed by two concentric spheres. The view factor of a point of inner sphere with respect to outer sphere is
A)
0.0
B)
0.5
C)
1.0
D)
none of these
For two concentric spheres forming an enclosure, the entire radiation leaving any point on the inner sphere can only strike the outer sphere. Hence, the view factor of a point on the inner sphere with respect to the outer sphere is 1.0. Option (a) is incorrect because the outer sphere is not hidden. Option (b) is incorrect because only half the radiation does not go to the outer sphere in this geometry. Therefore, the correct answer is (c) 1.0.
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.
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.
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.
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.
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.
By taking the ratio of pressure force and inertia force, the following number may be obtained
A)
Weber number
B)
Euler number
C)
Froude number
D)
Mach number
The Euler number is defined as the ratio of pressure force to inertia force in fluid flow. It is commonly written as Eu = p / (ρV^2) in nondimensional form.
Why others are incorrect:
- Weber number = inertia force / surface tension force.
- Froude number = inertia force / gravitational force.
- Mach number = flow velocity / speed of sound.
Therefore, the correct answer is Euler number.
In any natural process, the difference between the final entropy and initial entropy is
A)
positive
B)
negative
C)
nil
D)
indeterminate
For any natural (spontaneous) process, the entropy of the universe increases according to the second law of thermodynamics. Therefore, the final entropy is greater than the initial entropy, so the change in entropy is positive. It is not negative or nil for a natural process. 'Indeterminate' is incorrect because the direction is fixed by the second law.
The maximum pressure ratio in an actual single stage centrifugal compressor will be about
A)
1 : 15
B)
1 : 10
C)
1 : 4
D)
1 : 1.5
A single-stage centrifugal compressor can achieve only a limited pressure ratio in practice because of diffuser losses, temperature rise, and flow limitations. The maximum pressure ratio for an actual single-stage centrifugal compressor is about 4:1. Hence, among the given options, 1 : 4 is correct. The other ratios are either too high for a single stage (1:10, 1:15) or too low (1:1.5).
The gray body shape factor for radiant heat exchange between two long parallel plates of equal area and each having an emissivity of 0.4 is
A)
1
B)
4
C)
¼
D)
0.4
For two long parallel plates of equal area, the geometric view factor between the plates is 1. In gray-body radiation exchange, the effective gray-body shape factor reduces to the surface emissivity when the two plates are identical and each has emissivity ε = 0.4. Hence the gray body shape factor is 0.4. The other options 1, 4, and 1/4 do not match the given emissivity-based result.
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.
The resultant hydrostatic force acts through a point known as
A)
centre of gravity
B)
centre of pressure
C)
centre of buoyancy
D)
centre of force
In hydrostatics, the pressure on a submerged surface varies with depth, so the total resultant force does not act at the centroid. It acts at a specific point called the centre of pressure.
- Centre of gravity: point where weight acts.
- Centre of buoyancy: point through which buoyant force acts.
- Centre of force: not the standard term for resultant hydrostatic force here.
Therefore, the correct answer is centre of pressure.