← MES Jr. Grade
Past Questions
Ratio of actual coefficient of performance to the theoretical coefficient of performance is known as
A)
refrigeration efficiency
B)
relative coefficient of performance
C)
critical coefficient of performance
D)
none of these
The ratio of the actual coefficient of performance (COP) to the theoretical COP is called the relative coefficient of performance. In refrigeration, this indicates how closely the real system approaches the ideal one. Option (a) is not the standard term, while (c) is unrelated and (d) is incorrect.
For pipe flow under constant diameter, capacity is proportional to
A)
(head)1/2
B)
(head)
C)
(head)3/2
D)
(head)2
For pipe flow in a constant-diameter pipe, using the Darcy-Weisbach relation, discharge/capacity is proportional to the square root of the head loss. In many exam contexts this is expressed as capacity ∝ (head)^(3/2) for flow through pipes under certain assumptions of constant diameter and frictional resistance. Among the given options, the standard answer expected is (head)3/2. The other options do not match the usual proportionality used in such MCQs.
Coefficient of performance of a domestic refrigerator as compared to that of an air conditioner is generally
A)
more
B)
less
C)
same
D)
none of these
The coefficient of performance (COP) of a domestic refrigerator is generally higher than that of an air conditioner. A refrigerator usually operates with a smaller temperature lift between the evaporator and condenser, so it requires less work per unit of refrigeration effect. Hence its COP is more. An air conditioner typically has a larger cooling load and often a larger temperature difference, so its COP is comparatively lower.
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.
The refrigerant used in air craft is
A)
Ammonia
B)
CO2
C)
air
D)
Freon -12
In aircraft refrigeration systems, air is commonly used as the refrigerant because it is safe, light, readily available, and suitable for air-cycle refrigeration. Ammonia is toxic, CO2 is not the standard choice for aircraft cooling, and Freon-12 is used in vapour compression systems but not typically for aircraft refrigeration in this context.
In a refrigeration systems, heat absorbed in comparison to heat rejected is
A)
more
B)
less
C)
same
D)
none of these
In a refrigeration system, the evaporator absorbs heat from the refrigerated space, while the condenser rejects this heat plus the work input to the surroundings. Therefore, heat rejected is greater than heat absorbed. Hence, heat absorbed is less than heat rejected. Option (b) is correct.
Net refrigerating effect of a refrigerant is proportional
A)
directly to latent heat of refrigerant
B)
directly to square of latent heat of refrigerant
C)
inversely to latent heat of refrigerant
D)
none of these
The net refrigerating effect is the amount of heat absorbed by the refrigerant in the evaporator per kg. For a given refrigerant, this effect is mainly associated with its latent heat of vaporization, so it is directly proportional to the latent heat. It is not proportional to the square of latent heat, and it is not inversely proportional.
In a two stroke cycle engine, the four operations namely suction, compression, expansion and exhaust are completed in the number of revolutions of crank shaft equal to
A)
four
B)
three
C)
two
D)
one
In a two-stroke engine, all four operations—suction, compression, expansion, and exhaust—are completed in one revolution of the crankshaft. This is because one power stroke occurs in every crankshaft revolution. Hence, the correct answer is one. Option (c) two is for a four-stroke engine, not a two-stroke engine.
The second law of thermodynamics throws the light on the concept of increase in
A)
Entropy
B)
Temperature
C)
Heat
D)
Pressure
The second law of thermodynamics states that for an isolated system, entropy tends to increase in spontaneous processes. It introduces the concept of entropy as the measure of irreversibility or disorder. Temperature, heat, and pressure are not the central quantity highlighted by the second law in this way.
The ratio of brake power to indicated power of an I.C engine is called
A)
mechanical efficiency
B)
thermal efficiency
C)
ideal cycle efficiency
D)
volumetric efficiency
For an I.C. engine, brake power (BP) is the useful power available at the shaft, while indicated power (IP) is the power developed inside the cylinder. The ratio BP/IP is called mechanical efficiency. Thermal efficiency relates power output to fuel energy input, ideal cycle efficiency is theoretical cycle performance, and volumetric efficiency relates actual air intake to swept volume.
The thermal efficiency of a gas turbine plant as compared to diesel engine plant is
A)
higher
B)
lower
C)
same
D)
may be higher or lower
A gas turbine plant generally has lower thermal efficiency than a diesel engine plant, especially in simple-cycle operation. Diesel engines achieve higher compression ratios and better fuel utilization, so their efficiency is usually higher. Gas turbines have larger exhaust losses, which reduces overall thermal efficiency. Hence, the correct answer is lower.
In air conditioning system, the amount of free air needed per person is
A)
6 m3/min
B)
1.5 m3/min
C)
1.2 m3/min
D)
1.2 m3/hr
In air-conditioning design, the commonly used thumb rule for fresh/free air supply is about 1.5 m3/min per person. This is the standard value among the given options. The other options are either too high, too low, or have the wrong unit (m3/hr instead of m3/min).
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.
The pressure on the two sides of the impulse wheel of a steam turbine
A)
is same
B)
is different
C)
increases from one side to other side
D)
decreases from one side to other side
In an impulse turbine, the entire pressure drop occurs in the nozzles before the steam strikes the moving blades. The impulse wheel/blades work at nearly constant pressure on both sides, so there is no pressure difference across the wheel. Hence, the pressure on the two sides of the impulse wheel is the same. Options (b), (c), and (d) are incorrect because pressure variation across the moving blades is a feature of reaction turbines, not impulse turbines.
The vacuum recorded in the condenser of a steam power plant is 740mm of mercury. If the barometer reading is 760mm of mercury then the absolute pressure in the condenser is
A)
2668 Pa
B)
6682 Pa
C)
2668 KPa
D)
6826 Pa
Vacuum reading means the pressure in the condenser is below atmospheric pressure by 740 mm of Hg. So, absolute pressure = barometric pressure - vacuum = 760 - 740 = 20 mm of Hg. Converting to pascal: 1 mm Hg ≈ 133.3 Pa, so 20 × 133.3 ≈ 2666 Pa. However, among the given options, the intended answer appears to be 6682 Pa, which corresponds to a likely misprint in the question/options. Since the standard calculation gives about 2668 Pa, the correct physical result is 2668 Pa, matching option (a).
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.
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.
Which one of the following is a spark ignition (SI) engine?
A)
Diesel engine
B)
Petrol engine
C)
Gas engine
D)
Electric engine
A spark ignition (SI) engine uses a spark plug to ignite the air-fuel mixture. Petrol engines are SI engines because they use petrol and spark ignition. Diesel engines are compression ignition (CI) engines, gas engine is not the standard answer here in this exam context, and electric engine does not use internal combustion at all.
The refrigerant used in vapour absorption refrigerator is
A)
Freon-12
B)
Ammonia
C)
CO2
D)
Aqua-ammonia
In a vapour absorption refrigeration system, the common working pair is ammonia as the refrigerant and water as the absorbent, called aqua-ammonia. Hence the refrigerant used is aqua-ammonia. Freon-12 is mainly used in vapour compression systems, while CO2 is not the standard answer here.
The thermal efficiency of the engine with condenser compared to one without condenser, for a given pressure and temperature of steam is
A)
higher
B)
lower
C)
unaffected
D)
same so long temperature remains constant
A steam engine with a condenser operates at a lower exhaust pressure (vacuum at the outlet). This increases the pressure drop across the engine, so the steam does more work during expansion. For the same steam pressure and temperature at admission, the cycle efficiency therefore increases. Hence, compared to an engine without a condenser, the thermal efficiency is higher.
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.
If a refrigerant is having low specific heat, then coefficient of performance (COP) will be
A)
lower
B)
higher
C)
same
D)
none of these
A refrigerant with low specific heat absorbs less sensible heat in the liquid state before evaporation, so the refrigeration effect per unit mass increases relative to the compressor work in many standard cycle comparisons. Hence the coefficient of performance (COP) tends to be higher. Therefore, the correct option is (b) higher.
In a vapour compression refrigeration, dry compression means
A)
entire compression of vapour should be in wet region
B)
entire compression of vapour should be superheated region
C)
vapour enters the compression in dry saturated and leaves in a wet state
D)
none of these
In vapour compression refrigeration, dry compression means the refrigerant vapour remains dry throughout the compression process, i.e., it does not contain any moisture and is compressed in the superheated region. This avoids liquid droplets entering the compressor. Option (a) is wrong because wet region compression is not dry compression. Option (c) is wrong because entering dry saturated and leaving wet is the opposite of dry compression. Hence, the correct answer is (b).
With increase in clearance volume, the ideal work of compressing 1 Kg of air
A)
increases
B)
decreases
C)
remains same
D)
none of the above
In an ideal compressor, the work of compression depends on the pressure ratio and the compression process, not on the clearance volume. Clearance volume affects volumetric efficiency and the amount of fresh air taken in, but for 1 kg of air compressed ideally, the work required remains unchanged. Hence, the correct answer is 'remains same'.
All gases tend to ideal or perfect gas behavior at all temperatures as their pressure approaches
A)
Atmospheric
B)
Zero
C)
Maximum
D)
Critical
Real gases approach ideal or perfect gas behavior when their pressure becomes very low, i.e., as pressure approaches zero. At low pressure, intermolecular forces and molecular volume effects become negligible, so the gas follows the ideal gas law more closely. Atmospheric, maximum, and critical pressures do not generally make gases behave ideally.