← MES Jr. Grade
Past Questions
During adiabatic saturation process on unsaturated air, the
A)
dry bulb temperature remains constant
B)
wet dry bulb temperature remains constant
C)
dew point temperature remains constant
D)
saturation temperature remains constant
In an adiabatic saturation process, unsaturated air is brought into contact with water in an insulated system. Evaporation continues until the air becomes saturated, and the process reaches the adiabatic saturation temperature (also called the saturation temperature for that condition). This temperature remains constant for the idealized process. The dry-bulb temperature decreases, and the dew point does not remain constant. Hence, the correct option is (d).
The first law of thermodynamics throws the light on the concept of
A)
Entropy
B)
Energy
C)
Strain
D)
Internal Energy
The first law of thermodynamics is the law of conservation of energy. It states that energy can neither be created nor destroyed, only converted from one form to another. Hence, it throws light on the concept of energy. Entropy is associated with the second law, strain is a mechanics term, and internal energy is a thermodynamic property but not the main concept highlighted by the first law.
An optical pyrometer can measure temperatures up to a limit of
A)
1000ºC
B)
2000ºC
C)
3000ºC
D)
4000ºC
An optical pyrometer is used for very high temperatures, typically in the range where contact thermometers fail. In standard electrical engineering instrumentation texts, its upper measuring limit is about 3000ºC. Hence option (c) is correct. 1000ºC is too low for an optical pyrometer, while 4000ºC is beyond the usual practical limit.
Brine is always used as a secondary refrigerant in a
A)
cold storage plants
B)
milk chilling plants
C)
cinema hall air conditioning plants
D)
ice plants
Brine is a common secondary refrigerant used in cold storage plants because it can circulate through coils and maintain low temperatures without freezing easily. In such systems, the primary refrigerant cools the brine, and the brine then carries the cooling effect to the storage space. Milk chilling plants and cinema hall air conditioning plants generally use direct refrigeration or chilled water systems, while ice plants use direct refrigeration for ice making rather than brine as the usual secondary refrigerant.
The ratio of specific heats of a gas at constant pressure and at constant volume
A)
varies with temperature
B)
varies with pressure
C)
is always constant
D)
none of the above
The ratio of specific heats is denoted by γ = Cp/Cv. For a given gas in the ideal-gas approximation, Cp and Cv are constants for a fixed composition, so their ratio is also constant. Hence the correct option is (c). Options (a) and (b) are not generally true for the standard thermodynamics treatment used in such exams.
Mechanical friction occurring during a process due to some external source is an example of
A)
Reversibility
B)
Irreversibility
C)
Availability
D)
Unavailability
Mechanical friction caused by an external source produces dissipative effects and entropy generation, so the process cannot be exactly reversed without leaving changes in the system and surroundings. Hence it is an example of irreversibility. Reversibility would require no friction or other dissipative losses. Availability and unavailability are related to useful work potential, not the nature of friction itself.
In a free vortex motion, tangential velocity of the water particles is proportional to
A)
R
B)
R2
C)
1/R
D)
1/R2
In a free vortex, there is no external torque acting on the fluid, so angular momentum is conserved. Hence, the tangential velocity varies inversely with radius: v ∝ 1/R. Therefore, the correct option is (c). Options (a), (b), and (d) do not satisfy the free-vortex relation.
In an extensive property of a thermodynamic system
A)
Extensive heat is transferred
B)
Extensive work is done
C)
Extensive energy is utilized
D)
None of the above
An extensive property depends on the size or mass of the system, such as mass, volume, total energy, and entropy. Heat and work are not properties; they are path functions, so the terms 'extensive heat' and 'extensive work' are incorrect. 'Extensive energy' is also not the standard statement here because energy is a property, but the question asks what is done/transferred in an extensive property context, and none of the given statements is correct.
In reciprocating air compressor the method of controlling the quantity delivered is done by
A)
throttle control
B)
blow-off control
C)
clearance control
D)
all of the above
In a reciprocating air compressor, the quantity delivered can be controlled by several methods: throttle control, blow-off control, and clearance control. Throttle control reduces the intake pressure, blow-off control diverts excess air, and clearance control varies the clearance volume to reduce delivery. Since all three are valid methods, the correct answer is 'all of the above'.
The average kinetic energy of translation possessed by molecules can be determined if the parameter measured is
A)
Pressure
B)
Volume
C)
Temperature
D)
Entropy
For an ideal gas, the average translational kinetic energy of molecules is directly proportional to absolute temperature: \(\frac{3}{2}kT\) per molecule. Therefore, if temperature is measured, the average kinetic energy can be determined. Pressure, volume, and entropy do not directly give the average translational kinetic energy.
Specific heat is the amount of heat needed to raise the temperature
A)
by unit degree of a substance
B)
by unit degree of unit mass
C)
of a unit mass by ten
D)
None of the above
Specific heat (specific heat capacity) is defined as the amount of heat required to raise the temperature of unit mass of a substance by 1 degree. Option (b) matches this definition. Option (a) is incomplete because it does not specify unit mass, and option (c) is incorrect.
Psychometric process is
A)
sensible heating
B)
humidification
C)
dehumidification
D)
all of these
A psychrometric process is any process involving a change in the state of moist air on the psychrometric chart. This includes sensible heating, humidification, dehumidification, cooling, and combinations of these. Since all the listed processes are psychrometric processes, the correct answer is 'all of these'.
A barometer reads 760mm of mercury, its equivalent pressure in Bar is
A)
4.2
B)
420
C)
0.42
D)
42
A barometer reading of 760 mm of mercury corresponds to 1 atmosphere, which is approximately 1.013 bar. However, in many engineering exam contexts, the intended conversion is taken as 760 mm Hg = 1.013 × 10^5 Pa = 1.013 bar, and among the given options the closest standard exam answer is 0.42 only if a different unit convention is being used. But here the options clearly suggest a likely printing/scale issue. Since 760 mm Hg is about 1 bar, none of the options match exactly. If the question intended 760 mm of water or another unit, 0.42 bar could arise, but for mercury it does not. Therefore the question appears inconsistent with the options.
The compression ratio of Petrol engine is in the range of
A)
2 to 3
B)
7 to 10
C)
16 to 20
D)
above 20
In a petrol (spark-ignition) engine, the compression ratio is generally kept moderate to avoid knocking. Typical compression ratios are in the range of about 7:1 to 10:1. Option (a) is too low for normal petrol engines, while (c) and (d) are characteristic of diesel engines, which use much higher compression ratios.
The reheat factor in steam turbine depends on
A)
exit pressure only
B)
stage efficiency only
C)
initial pressure and temperature only
D)
all the above
The reheat factor in a steam turbine is influenced by the turbine operating conditions and stage performance. It depends on the exit pressure, stage efficiency, and also the initial steam pressure and temperature. Hence, all the given factors affect the reheat factor. Therefore, option (d) is correct.
In a refrigeration cycle, the heat is absorbed by a refrigerant in a
A)
evaporator
B)
condenser
C)
compressor
D)
expansion valve
In a refrigeration cycle, the refrigerant absorbs heat from the space to be cooled in the evaporator. Here the low-pressure refrigerant evaporates by taking in latent heat. The condenser rejects heat, the compressor raises pressure and temperature, and the expansion valve reduces pressure.
In a four cylinder Petrol engine the standard firing order is
A)
1-2-3-4
B)
1-4-3-2
C)
1-3-2-4
D)
1-3-4-2
In a 4-cylinder petrol engine, the commonly used standard firing order is 1-3-4-2. This sequence gives better engine balance and smoother operation by spacing the power strokes evenly. The other options are not the standard firing order for a four-cylinder petrol engine.
In a regenerative feed heating cycle, the optimum value of the fraction of steam extracted for feed heating
A)
decreases with increase in Rankine cycle efficiency
B)
increases with increase in Rankine cycle efficiency
C)
is unaffected by increase in Rankine cycle efficiency
D)
none of the above
In a regenerative feed heating cycle, the fraction of steam extracted for feed heating is chosen to maximize the overall cycle performance. As the Rankine cycle efficiency increases, the need for large extraction fractions reduces because the cycle is already operating more effectively. Therefore, the optimum extracted steam fraction decreases with increase in Rankine cycle efficiency. Hence, option (a) is correct.
A system comprising of a single phase only is usually known as
A)
open system
B)
closed system
C)
homogeneous system
D)
heterogeneous system
A system consisting of only one phase is called a homogeneous system. In such a system, the properties are uniform throughout. An open system and a closed system describe whether mass can cross the boundary, not the number of phases. A heterogeneous system contains two or more phases.
Sometimes the evaporator is not cooled properly and it is due to
A)
leakage in refrigerator
B)
faulty thermostat
C)
frozen oil
D)
lot of frozen ice
If a lot of ice accumulates on the evaporator, it acts as an insulating layer and reduces heat transfer from the refrigerated space to the evaporator. As a result, the evaporator is not cooled properly. A faulty thermostat may affect compressor operation, but the direct cause of poor evaporator cooling here is ice build-up. Leakage and frozen oil are not the usual immediate reason for this symptom.
Thermal efficiency of a closed cycle gas turbine plant increases by
A)
reheating
B)
intercooling
C)
regenerator
D)
all of the above
In a closed-cycle gas turbine, a regenerator recovers heat from the turbine exhaust and uses it to preheat the compressed air before combustion/heating. This reduces the external heat input required, thereby increasing thermal efficiency. Reheating increases work output but generally does not improve thermal efficiency by itself, and intercooling reduces compressor work but also usually lowers cycle efficiency unless combined with regeneration. Hence, the correct answer is regenerator.
In a refrigeration cycle, the moisture is to be removed before it enters the
A)
cold side of system
B)
evaporator
C)
compressor
D)
condenser
In a refrigeration cycle, moisture must be removed from the refrigerant before it enters the compressor. If moisture enters the compressor, it can cause corrosion, oil dilution, and possible mechanical damage. Therefore, a drier is used to remove moisture before the compressor. The evaporator and condenser are not the components where moisture removal is required in this context.
For a closed system, the difference between the heat added to the system and the work done by the gas, is equal to the change in
A)
enthalpy
B)
entropy
C)
internal energy
D)
temperature
For a closed system, the first law of thermodynamics gives: Q - W = ΔU, where Q is heat added to the system, W is work done by the gas, and ΔU is the change in internal energy. Therefore, the difference between heat added and work done equals the change in internal energy. Enthalpy, entropy, and temperature are not given by this direct relation.
A thermocouple consists of two dissimilar metals or alloys which develop e.m.f. when the reference and measuring junctions are at different level of
A)
Voltage
B)
Temperature
C)
Flux
D)
Thermions
A thermocouple works on the Seebeck effect: when the measuring junction and reference junction are at different temperatures, an e.m.f. is produced. Hence the correct answer is Temperature. Voltage, flux, and thermions are not the operating principle of a thermocouple.
Willan’s line is a curve plotted of steam consumption rate in steam engine versus
A)
speed
B)
indicated power
C)
frictional power
D)
brake power
Willan’s line is the graph obtained by plotting steam consumption rate against indicated power for a steam engine. It is used to estimate the no-load steam consumption and the mechanical efficiency of the engine. Hence, the correct option is indicated power. The other options are incorrect because Willan’s line is not defined with speed, frictional power, or brake power.