4791 + Mcqs in Mechanical Engineering Page 37 McqOptions

1801.	Thermal conductivity of solid metals __________ with rise in temperature.
A.	remains same
B.	decreases
C.	increases
Answer» C. increases

Discussion

1802.	The heating of air, without any change in its specific humidity, is known as sensible heating.
A.	True
B.	False
Answer» B. False

Discussion

1803.	In order to collect liquid refrigerant and to prevent it from going to a __________ , a device known as accumulator is used at the suction of compressor.
A.	compressor
B.	condenser
C.	expansion valve
D.	evaporator
Answer» B. condenser

Discussion

1804.	Which of the following refrigerant has the lowest boiling point?
A.	Ammonia
B.	Carbon dioxide
C.	Sulphur dioxide
D.	R-12
Answer» C. Sulphur dioxide

Discussion

1805.	The coefficient of performance of vapour compression refrigeration system is quite __________ as compared to air refrigeration system.
A.	low
B.	high
Answer» C.

Discussion

1806.	Wein's law states that the wave length corresponding to __________ is proportional to the absolute temperature.
A.	minimum energy
B.	maximum energy
Answer» C.

Discussion

1807.	During sensible cooling of air, the relative humidity increases.
A.	Yes
B.	No
Answer» B. No

Discussion

1808.	In a refrigeration system, the expansion device is connected between the
A.	compressor and condenser
B.	condenser and receiver
C.	receiver and evaporator
D.	evaporator and compressor
Answer» D. evaporator and compressor

Discussion

1809.	The heat rejection factor (HRF) is given by
A.	1 + C.O.P
B.	1 - C.O.P.
C.	<img src="/_files/images/mechanical-engineering/heat-transfer-refrigeration-and-air-conditioning/425-264-1.png">
D.	<img src="/_files/images/mechanical-engineering/heat-transfer-refrigeration-and-air-conditioning/425-264-2.png">
Answer» D. <img src="/_files/images/mechanical-engineering/heat-transfer-refrigeration-and-air-conditioning/425-264-2.png">

Discussion

1810.	A furnace is made of a red brick wall of thickness 0.5 m and conductivity 0.7 W/mK. For the same heat loss and temperature drop, this can be replaced by a layer of diatomite earth of conductivity 0.14 W/mK and thickness
A.	0.5 m
B.	0.1 m
C.	0.2 m
D.	0.5 m
Answer» C. 0.2 m

Discussion

1811.	The human body feels comfortable when the heat stored in the body is
A.	positive
B.	negative
C.	zero
D.	none of these
Answer» D. none of these

Discussion

1812.	The process of heat transfer from one particle of the body to another is called conduction, when the particles of the body
A.	move actually
B.	do not move actually
C.	affect the intervening medium
D.	does not affect the intervening medium
Answer» C. affect the intervening medium

Discussion

1813.	A Bell Coleman refrigerator working on dense air system as compared to open air system, for the same range of temperature, results in __________ power per tonne of refrigeration.
A.	same
B.	lower
C.	higher
Answer» C. higher

Discussion

1814.	The freezing point of sulphur dioxide is
A.	-56.6 C
B.	-75.2 C
C.	-77.7 C
D.	-135.8 C
Answer» C. -77.7 C

Discussion

1815.	The ratio of the energy absorbed by the body to the total energy falling on it, is called
A.	absorptive power
B.	emissive power
C.	emissivity
D.	none of these
Answer» B. emissive power

Discussion

1816.	The vertical and uniformly spaced lines on a psychrometric chart indicates
A.	dry bulb temperature
B.	wet bulb temperature
C.	dew point temperature
D.	specific humidity
Answer» B. wet bulb temperature

Discussion

1817.	The amount of heat flow through a body by conduction is
A.	directly proportional to the surface area of the body
B.	directly proportional to the temperature difference on the two faces of the body
C.	inversely proportional to the thickness of the body
D.	all of the above
Answer» E.

Discussion

1818.	Which of the following refrigerant is highly toxic and flammable?
A.	Ammonia
B.	Carbon dioxide
C.	Sulphur dioxide
D.	R-12
Answer» B. Carbon dioxide

Discussion

1819.	A Bell Coleman refrigerator working on dense air system as compared to open air system, for the same range of temperature, results in higher coefficient of performance.
A.	Agree
B.	Disagree
Answer» B. Disagree

Discussion

1820.	The ratio of surface convection resistance to the internal conduction resistance is known as
A.	Grashoff number
B.	Biot number
C.	Stanton number
D.	Prandtl number
Answer» C. Stanton number

Discussion

1821.	Relative humidity is given by (where pv = Partial pressure of water vapour, pb = Barometric pressure, ps = Pressure of saturated air, pd = Pressure at dry bulb temperature, pw = Saturation pressure corresponding to wet bulb temperature, and = Degree of saturation)
A.	<img src="/_files/images/mechanical-engineering/heat-transfer-refrigeration-and-air-conditioning/429-312-1.png">
B.	<img src="/_files/images/mechanical-engineering/heat-transfer-refrigeration-and-air-conditioning/429-312-2.png">
C.	<img src="/_files/images/mechanical-engineering/heat-transfer-refrigeration-and-air-conditioning/429-312-3.png">
D.	none of these
Answer» C. <img src="/_files/images/mechanical-engineering/heat-transfer-refrigeration-and-air-conditioning/429-312-3.png">

Discussion

1822.	In a reversed Brayton cycle, the heat is absorbed by the air during
A.	isentropic compression process
B.	constant pressure cooling process
C.	isentropic expansion process
D.	constant pressure expansion process
Answer» E.

Discussion

1823.	Wet bulb temperature is the temperature of air recorded by a thermometer, when
A.	it is not effected by the moisture present in the air
B.	its bulb is surrounded by a wet cloth exposed to the air
C.	the moisture present in it begins to condense
D.	none of the above
Answer» C. the moisture present in it begins to condense

Discussion

1824.	When there is an addition of water vapour to the air of enclosed space, a gain in __________ is said to occur.
A.	sensible heat
B.	latent heat
Answer» C.

Discussion

1825.	The relative humidity __________ as air gets drier.
A.	increases
B.	decreases
Answer» B. decreases

Discussion

1826.	When is absorptivity, is reflectivity and is transmittivity, then for a diathermanous body,
A.	= 1, = 0 and = 0
B.	= 0, = 1 and = 0
C.	= 0, = 0 and = 1
D.	+ = 1 and = 0
Answer» E.

Discussion

1827.	A boot-strap air cooling system has
A.	one heat exchanger
B.	two heat exchangers
C.	three heat exchangers
D.	four heat exchangers
Answer» C. three heat exchangers

Discussion

1828.	The boiling point of __________ is -10.5 C.
A.	ammonia
B.	R-12
C.	sulphur dioxide
D.	carbon dioxide
Answer» D. carbon dioxide

Discussion

1829.	The operating pressure for refrigerating units using R-12 as a refrigerant is
A.	2 bar
B.	8 bar
C.	15 bar
D.	30 bar
Answer» C. 15 bar

Discussion

1830.	The minimum temperature to which water can be cooled in a cooling tower is
A.	dew point temperature of air
B.	wet bulb temperature of air
C.	dry bulb temperature of air
D.	ambient air temperature
Answer» C. dry bulb temperature of air

Discussion

1831.	The C.O.P. of a Carnot refrigerator in winter will be __________ as compared to C.O.P. in summer.
A.	same
B.	lower
C.	higher
Answer» D.

Discussion

1832.	One tonne of refrigeration (1TR) means that the heat removing capacity is
A.	21 kJ/min
B.	210 kJ/min
C.	420 kJ/min
D.	620 kJ/min
Answer» C. 420 kJ/min

Discussion

1833.	The radiation emitted by a black body is known as
A.	black radiation
B.	full radiation
C.	total radiation
D.	all of these
Answer» E.

Discussion

1834.	According to Newton's law of cooling, the heat transfer from a hot body to a cold body is
A.	directly proportional to the surface area
B.	directly proportional to the difference of temperatures between the two bodies
C.	either (a) or (b)
D.	both (a) and (b)
Answer» E.

Discussion

1835.	The freezing point of carbon dioxide is equal to boiling point of R-12.
A.	Correct
B.	Incorrect
Answer» C.

Discussion

1836.	The condition of refrigerant as it leaves the compressor in a vapour compression system is
A.	saturated liquid
B.	wet vapour
C.	dry saturated vapour
D.	superheated vapour
Answer» E.

Discussion

1837.	The condition of refrigerant after passing through the expansion or throttle valve, in a vapour compression system is
A.	high pressure saturated liquid
B.	wet vapour
C.	very wet vapour
D.	dry vapour
Answer» D. dry vapour

Discussion

1838.	The process of adding moisture to the air, without change in its dry bulb temperature, is known as humidification.
A.	Agree
B.	Disagree
Answer» B. Disagree

Discussion

1839.	In case of liquids and gases, the heat transfer takes place according to
A.	conduction
B.	convection
C.	radiation
D.	none of these
Answer» C. radiation

Discussion

1840.	The sensible heat factor during the heating and humidification process is given by (where h1 = Enthalpy of air entering the heating coil, h2 = Enthalpy of air leaving the heating coil, and hA = Enthalpy of air at the end of humidification process)
A.	<img src="/_files/images/mechanical-engineering/heat-transfer-refrigeration-and-air-conditioning/434-375-1.png">
B.	<img src="/_files/images/mechanical-engineering/heat-transfer-refrigeration-and-air-conditioning/434-375-2.png">
C.	<img src="/_files/images/mechanical-engineering/heat-transfer-refrigeration-and-air-conditioning/434-375-3.png">
D.	<img src="/_files/images/mechanical-engineering/heat-transfer-refrigeration-and-air-conditioning/434-375-4.png">
Answer» E.

Discussion

1841.	The average value of thermal conductivity for water at 20 C saturate is about 0.51.
A.	True
B.	False
Answer» B. False

Discussion

1842.	In aqua-ammonia absorption refrigeration system, incomplete rectification leads to accumulation of water in
A.	condenser
B.	evaporator
C.	absorber
D.	none of these
Answer» B. evaporator

Discussion

1843.	The centrifugal compressors are generally used for refrigerants that require
A.	small displacements and low condensing pressures
B.	large displacements and high condensing pressures
C.	small displacements and high condensing pressures
D.	large displacements and low condensing pressures
Answer» E.

Discussion

1844.	According to Stefan's law, the total radiation from a black body per second per unit area is directly proportional to the fourth power of the absolute temperature.
A.	Correct
B.	Incorrect
Answer» B. Incorrect

Discussion

1845.	In electrolux refrigerator
A.	ammonia is absorbed in hydrogen
B.	ammonia is absorbed in water
C.	ammonia evaporates in hydrogen
D.	hydrogen evaporates in ammonia
Answer» D. hydrogen evaporates in ammonia

Discussion

1846.	Two long parallel surfaces each of emissivity 0.7 are maintained at different temperatures and accordingly have radiation heat exchange between them. It is desired to reduce 75% of the radiant heat transfer by inserting thin parallel shields of emissivity 1 on both sides. The number of shields should be
A.	one
B.	two
C.	three
D.	four
Answer» D. four

Discussion

1847.	The water, alcohol and ammonia have same refrigerating effect at different altitudes.
A.	Yes
B.	No
Answer» C.

Discussion

1848.	In mechanical refrigeration system, the refrigerant occurs as liquid between condenser and expansion valve.
A.	True
B.	False
Answer» B. False

Discussion

1849.	A heat pump working on a reversed Carnot cycle has a C.O.P. of 5. It works as a refrigerator taking 1 kW of work input. The refrigerating effect will be
A.	1 kW
B.	2 kW
C.	3 kW
D.	4 kW
Answer» E.

Discussion

1850.	Which of the following is a case hardening process?
A.	Carburising
B.	Cyaniding
C.	Nitriding
D.	all of these
Answer» E.

Discussion

Explore topic-wise MCQs in Engineering.

Thermal conductivity of solid metals __________ with rise in temperature.

The heating of air, without any change in its specific humidity, is known as sensible heating.

In order to collect liquid refrigerant and to prevent it from going to a __________ , a device known as accumulator is used at the suction of compressor.

Which of the following refrigerant has the lowest boiling point?

The coefficient of performance of vapour compression refrigeration system is quite __________ as compared to air refrigeration system.

Wein's law states that the wave length corresponding to __________ is proportional to the absolute temperature.

During sensible cooling of air, the relative humidity increases.

In a refrigeration system, the expansion device is connected between the

The heat rejection factor (HRF) is given by

A furnace is made of a red brick wall of thickness 0.5 m and conductivity 0.7 W/mK. For the same heat loss and temperature drop, this can be replaced by a layer of diatomite earth of conductivity 0.14 W/mK and thickness

The human body feels comfortable when the heat stored in the body is

The process of heat transfer from one particle of the body to another is called conduction, when the particles of the body

A Bell Coleman refrigerator working on dense air system as compared to open air system, for the same range of temperature, results in __________ power per tonne of refrigeration.

The freezing point of sulphur dioxide is

The ratio of the energy absorbed by the body to the total energy falling on it, is called

The vertical and uniformly spaced lines on a psychrometric chart indicates

The amount of heat flow through a body by conduction is

Which of the following refrigerant is highly toxic and flammable?

A Bell Coleman refrigerator working on dense air system as compared to open air system, for the same range of temperature, results in higher coefficient of performance.

The ratio of surface convection resistance to the internal conduction resistance is known as

Relative humidity is given by (where pv = Partial pressure of water vapour, pb = Barometric pressure, ps = Pressure of saturated air, pd = Pressure at dry bulb temperature, pw = Saturation pressure corresponding to wet bulb temperature, and = Degree of saturation)

In a reversed Brayton cycle, the heat is absorbed by the air during

Wet bulb temperature is the temperature of air recorded by a thermometer, when

When there is an addition of water vapour to the air of enclosed space, a gain in __________ is said to occur.

The relative humidity __________ as air gets drier.

When is absorptivity, is reflectivity and is transmittivity, then for a diathermanous body,

A boot-strap air cooling system has

The boiling point of __________ is -10.5 C.

The operating pressure for refrigerating units using R-12 as a refrigerant is

The minimum temperature to which water can be cooled in a cooling tower is

The C.O.P. of a Carnot refrigerator in winter will be __________ as compared to C.O.P. in summer.

One tonne of refrigeration (1TR) means that the heat removing capacity is

The radiation emitted by a black body is known as

According to Newton's law of cooling, the heat transfer from a hot body to a cold body is

The freezing point of carbon dioxide is equal to boiling point of R-12.

The condition of refrigerant as it leaves the compressor in a vapour compression system is

The condition of refrigerant after passing through the expansion or throttle valve, in a vapour compression system is

The process of adding moisture to the air, without change in its dry bulb temperature, is known as humidification.

In case of liquids and gases, the heat transfer takes place according to

The sensible heat factor during the heating and humidification process is given by (where h1 = Enthalpy of air entering the heating coil, h2 = Enthalpy of air leaving the heating coil, and hA = Enthalpy of air at the end of humidification process)

The average value of thermal conductivity for water at 20 C saturate is about 0.51.

In aqua-ammonia absorption refrigeration system, incomplete rectification leads to accumulation of water in

The centrifugal compressors are generally used for refrigerants that require

According to Stefan's law, the total radiation from a black body per second per unit area is directly proportional to the fourth power of the absolute temperature.

In electrolux refrigerator

The water, alcohol and ammonia have same refrigerating effect at different altitudes.

In mechanical refrigeration system, the refrigerant occurs as liquid between condenser and expansion valve.

A heat pump working on a reversed Carnot cycle has a C.O.P. of 5. It works as a refrigerator taking 1 kW of work input. The refrigerating effect will be

Which of the following is a case hardening process?