← MES Jr. Grade
Past Questions — 2012
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.
A fluid in which resistance of deformation is independent of the shear stress is known as
A)
Bingham plastic fluid
B)
Pseudo plastic fluid
C)
Dilatent fluid
D)
Newtonian fluid
A Newtonian fluid is one in which the viscosity (resistance to deformation) is constant and independent of the applied shear stress. In such fluids, shear stress is directly proportional to rate of shear strain. Bingham plastic fluids require a yield stress before they start flowing, while pseudo plastic and dilatent fluids are non-Newtonian and their viscosity changes with shear rate.
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).
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.
The coefficient of performance (COP) of a refrigerator working on a reversed Carnot cycle is 5. The ratio of highest absolute temperature to lowest temperature would be
A)
1.25
B)
1.3
C)
1.4
D)
1.2
For a refrigerator working on a reversed Carnot cycle,
COP = T_L / (T_H - T_L).
Given COP = 5,
5 = T_L / (T_H - T_L).
So, 5(T_H - T_L) = T_L
=> 5T_H - 5T_L = T_L
=> 5T_H = 6T_L
=> T_H / T_L = 6/5 = 1.2.
Hence, the ratio of highest absolute temperature to lowest absolute temperature is 1.2. The other options do not satisfy the Carnot COP relation.
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 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.
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.
Temperature of air recorded by an ordinary thermometer is known as
A)
wet bulb temperature
B)
dry bulb temperature
C)
dew point temperature
D)
saturation temperature
The temperature of air measured by an ordinary thermometer exposed to the air is called the dry bulb temperature. A wet bulb thermometer gives wet bulb temperature, dew point is the temperature at which moisture starts condensing, and saturation temperature refers to the temperature at which air becomes saturated with water vapour.
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).
A refrigerator works on
A)
Bell-Coleman cycle
B)
reversed Carnot cycle
C)
Carnot cycle
D)
both (a) and (b)
A refrigerator is a heat pump operating on a reversed cycle. In theory, the ideal refrigerator works on the reversed Carnot cycle, which gives the maximum possible COP. In practical air refrigeration systems, the Bell-Coleman cycle is used. Since both are associated with refrigerator operation, the correct option is both (a) and (b).
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.
In a four 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 four-stroke engine, one complete cycle requires 4 strokes of the piston: suction, compression, expansion (power), and exhaust. Since the crankshaft completes 2 revolutions for these 4 strokes, the correct answer is two revolutions. Hence, option (c) is correct.
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.
The bank of tubes at the back of domestic refrigerator are
A)
condenser tubes
B)
evaporated tubes
C)
refrigerant cooling tubes
D)
capillary tubes
In a domestic refrigerator, the coil/tube arrangement at the back is the condenser. It rejects heat from the hot, high-pressure refrigerant to the surrounding air, so the refrigerant condenses there. The evaporator is inside the cabinet, capillary tubes are small metering tubes, and 'refrigerant cooling tubes' is not the standard term.
The Zeroth law deals with thermal equilibrium and establishes a concept of following
A)
Thermal energy
B)
Temperature
C)
Heat
D)
Temperature
The Zeroth law of thermodynamics states that if two systems are each in thermal equilibrium with a third system, they are in thermal equilibrium with each other. This law establishes the concept of temperature as the property that determines thermal equilibrium. Hence, it deals with and defines the concept of temperature. Thermal energy and heat are different concepts, and option (d) is a duplicate of (b).
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'.
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 sensible heat added is 25,000 kJ/min and latent heat added is 20 kJ/sec, then sensible heat factor is equal to
A)
0.4
B)
0.5
C)
0.67
D)
0.7
Sensible Heat Factor (SHF) = Sensible Heat / (Sensible Heat + Latent Heat).
Given:
- Sensible heat added = 25,000 kJ/min
- Latent heat added = 20 kJ/sec = 20 × 60 = 1,200 kJ/min
So,
SHF = 25,000 / (25,000 + 1,200) = 25,000 / 26,200 ≈ 0.954
However, this value is not among the options, which suggests the question likely intends the units to be treated directly as given in a simplified exam context. If latent heat is taken as 20 kJ/min instead of 20 kJ/sec, then:
SHF = 25,000 / (25,000 + 20) ≈ 0.999, still not matching.
Since the options indicate a standard psychrometrics MCQ, the intended answer is most likely 0.7, but the numerical data as written is inconsistent.
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 sequence of process that eventually returns the working substance to its original state, is known as
A)
event
B)
thermodynamic cycle
C)
thermodynamic property
D)
none of the above
A sequence of thermodynamic processes that brings the working substance back to its initial state is called a thermodynamic cycle. In a cycle, the system ends where it started, so all state properties return to their original values. Option (a) event is unrelated, and option (c) thermodynamic property refers to characteristics like pressure, temperature, and volume, not a process sequence.
Which one of the following components is not boiler mounting?
A)
Safety valve
B)
Pressure gauge
C)
Feed pump
D)
Stop valve
Boiler mountings are the essential fittings attached to a boiler for safe operation. Safety valve, pressure gauge, and stop valve are all boiler mountings. A feed pump is not a mounting; it is a boiler accessory used to supply water to the boiler.
Which of the following is an extensive property of a thermodynamic system?
A)
Pressure
B)
Volume
C)
Temperature
D)
Density
An extensive property depends on the size or mass of the system. Volume increases when the amount of substance increases, so it is extensive. Pressure, temperature, and density do not depend on system size, so they are intensive properties.
Temperature of air recorded by a thermometer when the moisture present in it begins to condense, is known as
A)
wet bulb temperature
B)
dry bulb temperature
C)
dew point
D)
saturation temperature
The temperature at which the moisture (water vapour) in air starts condensing is called the dew point. It is the point where air becomes saturated and any further cooling causes condensation. Wet bulb temperature is measured by a wetted thermometer, dry bulb temperature is the normal air temperature, and saturation temperature is a broader term related to phase change at saturation, not specifically the onset of condensation in air.
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.