← MES Jr. Grade
Past Questions — 2012
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.
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 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.
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.
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.
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.
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.
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'.
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.
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).
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).
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.
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.
The effect of considering friction losses in steam nozzle for the same pressure ratio leads to
A)
increase in dryness fraction to exit steam
B)
decrease in dryness fraction to exit steam
C)
no change in the quality of exit steam
D)
none of the above
In a steam nozzle, friction causes irreversibility and reduces the kinetic energy gained for the same pressure drop. As a result, the expansion is less efficient and the steam at the nozzle exit contains more moisture. Therefore, the dryness fraction at exit decreases. Options (a) and (c) are incorrect because friction does not improve or leave unchanged the steam quality; it worsens it.
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.
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.
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.
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.
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 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.
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.
The velocity distribution in the turbulent boundary layer follows
A)
straight line law
B)
parabolic law
C)
hyperbolic law
D)
logarithmic law
In a turbulent boundary layer, the velocity distribution is commonly described by the logarithmic law (log law). This is because turbulent mixing causes a slower variation of velocity with distance from the wall compared to laminar flow. The straight line law is not generally valid for turbulent boundary layers, the parabolic law is associated with some laminar flow profiles, and the hyperbolic law is not the standard description here.
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).
Drag force on a 40:1 scale model of a ship is measured to be 10N. Force expected on the ship will be
A)
640kN
B)
520kN
C)
320kN
D)
80kN
For similar bodies moving in the same fluid under dynamic similarity, drag force scales with the square of the linear scale ratio for corresponding velocities. However, for a ship model test, the standard exam assumption here is that force varies as the cube of the scale ratio when comparing the actual ship and a 1/40 scale model under corresponding conditions.
Scale ratio = 40:1, so force ratio = 40^3 = 64,000.
Drag on model = 10 N
Drag on ship = 10 × 64,000 = 640,000 N = 640 kN.
But among the given options, the intended textbook answer for this common model-scaling question is 320 kN only if a factor of 2 due to resistance coefficient convention is applied; however, the standard similarity-based result is 640 kN, which is not listed. Since the question is from an exam MCQ, the closest matching listed option is not exact. Therefore, the question appears to have a likely mismatch in options.
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.