4791 + Mcqs in Mechanical Engineering Page 35 McqOptions

1701.	A low wet bulb temperature indicates very __________ humidity.
A.	low
B.	high
Answer» B. high

Discussion

1702.	The critical thickness of insulation is the ratio of thermal conductivity of the insulating material (k) to the heat transfer coefficient at the outer surface of the insulation (h0).
A.	True
B.	False
Answer» B. False

Discussion

1703.	A mixture of dry air and water vapour, when the air has diffused the maximum amount of water vapour into it, is called
A.	dry air
B.	moist air
C.	saturated air
D.	specific humidity
Answer» D. specific humidity

Discussion

1704.	The total pressure exerted by the mixture of air and water vapour is equal to the sum of pressures which each constituent would exert, if it occupied the same space by itself. This statement is called
A.	Kinetic theory of gases
B.	Newton's law of gases
C.	Dalton's law of partial pressures
D.	Avogadro's hypothesis
Answer» D. Avogadro's hypothesis

Discussion

1705.	For a given dry bulb temperature, as the relative humidity __________ the wet bulb temperature will increase.
A.	increases
B.	decreases
Answer» C.

Discussion

1706.	The temperature of air recorded by a thermometer, when the moisture present in it begins to condense, is called wet bulb temperature.
A.	Yes
B.	No
Answer» C.

Discussion

1707.	The drier in a refrigeration system removes moisture in the system.
A.	Correct
B.	Incorrect
Answer» B. Incorrect

Discussion

1708.	The boiling point of R-12 is about - 30 C.
A.	True
B.	False
Answer» B. False

Discussion

1709.	The material of pipe lines for a system using freon as a refrigerant should be
A.	brass
B.	copper
C.	steel
D.	aluminium
Answer» C. steel

Discussion

1710.	In a pressure enthalpy chart, the space to the left of the saturated liquid line represents
A.	wet vapour region
B.	superheated vapour region
C.	sub-cooled liquid region
D.	none of these
Answer» D. none of these

Discussion

1711.	When the lower temperature of a refrigerating machine is fixed, then the coefficient of performance can be improved by
A.	operating the machine at higher speeds
B.	operating the machine at lower speeds
C.	raising the higher temperature
D.	lowering the higher temperature
Answer» E.

Discussion

1712.	The refrigerant carbon dioxide is not widely used because of its __________ power require ments per tonne of refrigeration and high operating pressures.
A.	low
B.	high
Answer» C.

Discussion

1713.	The by-pass factor of a cooling coil decreases with
A.	decrease in fin spacing and increase in number of rows
B.	increase in fin spacing and increase in number of rows
C.	increase in fin spacing and decrease in number of rows
D.	decrease in fin spacing and decrease in number of rows
Answer» B. increase in fin spacing and increase in number of rows

Discussion

1714.	The cooling of air, without any change in its specific humidity, is known as sensible cooling.
A.	Correct
B.	Incorrect
Answer» B. Incorrect

Discussion

1715.	The capacity of the cooling tower and spray ponds __________ as the wet bulb temperature of air decreases.
A.	increases
B.	decreases
Answer» B. decreases

Discussion

1716.	In counter-current flow heat exchanger, the logarithmic temperature difference between the fluids is __________ as compared to parallel flow heat exchanger.
A.	same
B.	less
C.	greater
Answer» D.

Discussion

1717.	Dehydration is the process of removing water vapour from the surrounding air.
A.	True
B.	False
Answer» B. False

Discussion

1718.	Environmental protection agencies advice against the use of chloro-fluoro-carbon refrigerants since
A.	these react with water vapour and cause acid rain
B.	these react with plants and cause green-house effect
C.	these react with oxygen and cause its depletion
D.	these react with ozone layer
Answer» E.

Discussion

1719.	The relative coefficient of performance is equal to
A.	<img src="/_files/images/mechanical-engineering/heat-transfer-refrigeration-and-air-conditioning/414-125-1.png">
B.	<img src="/_files/images/mechanical-engineering/heat-transfer-refrigeration-and-air-conditioning/414-125-2.png">
C.	Actual C.O.P. x Theoretical C.O.P.
D.	none of these
Answer» C. Actual C.O.P. x Theoretical C.O.P.

Discussion

1720.	The boiling point of carbon dioxide is
A.	-20.5 C
B.	-50 C
C.	-63.3 C
D.	-78.3 C
Answer» E.

Discussion

1721.	The reciprocating refrigerant compressors are very suitable for
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» D. large displacements and low condensing pressures

Discussion

1722.	The final relative humidity of the air during cooling and dehumidification is generally __________ than that of entering air.
A.	lower
B.	higher
Answer» C.

Discussion

1723.	In a pressure enthalpy chart, the space between the saturated liquid line and saturated vapour line, represents sub-cooled liquid region.
A.	True
B.	False
Answer» C.

Discussion

1724.	Air refrigerator works on
A.	reversed Carnot cycle
B.	Bell Coleman cycle
C.	both (a) and ib)
D.	none of these
Answer» D. none of these

Discussion

1725.	The emissivity of a polished silver body is __________ as compared to black body.
A.	same
B.	low
C.	very low
D.	high
Answer» D. high

Discussion

1726.	Hydrogen is used in electrolux refrigeration system so as to __________ the rate of evaporation of the liquid ammonia passing through the evaporator.
A.	equalise
B.	reduce
C.	increase
Answer» D.

Discussion

1727.	The wet bulb temperature during sensible cooling of air
A.	remains constant
B.	increases
C.	decreases
Answer» D.

Discussion

1728.	In absorption vapour systems, the refrigerant widely used is R-12.
A.	Correct
B.	Incorrect
Answer» C.

Discussion

1729.	When tc1 and tc2 are the temperatures of cold fluid at entry and exit respectively and th1 and th2 are the temperatures of hot fluid at entry and exit point, and cold fluid has lower heat capacity rate as compared to hot fluid, then effectiveness of the heat exchanger is given by
A.	<img src="/_files/images/mechanical-engineering/heat-transfer-refrigeration-and-air-conditioning/409-72-1.png">
B.	<img src="/_files/images/mechanical-engineering/heat-transfer-refrigeration-and-air-conditioning/409-72-2.png">
C.	<img src="/_files/images/mechanical-engineering/heat-transfer-refrigeration-and-air-conditioning/409-72-3.png">
D.	<img src="/_files/images/mechanical-engineering/heat-transfer-refrigeration-and-air-conditioning/409-72-4.png">
Answer» E.

Discussion

1730.	In larger industrial and commercial reciprocating compression systems, refrigerent widely used is
A.	ammonia
B.	carbon dioxide
C.	sulphur dioxide
D.	R-12
Answer» B. carbon dioxide

Discussion

1731.	In a psychrometric chart, specific humidity (moisture content) lines are
A.	vertical and uniformly spaced
B.	horizontal and uniformly spaced
C.	horizontal and non-uniformly spaced
D.	curved lines
Answer» C. horizontal and non-uniformly spaced

Discussion

1732.	The expression Q = AT4 is called
A.	Fourier equation
B.	Stefan-Boltzmann equation
C.	Newton-Rikhmann equation
D.	Joseph-Stefan equation
Answer» C. Newton-Rikhmann equation

Discussion

1733.	Oil separator in a refrigeration cycle is installed
A.	before compressor
B.	between compressor and condenser
C.	between condenser and evaporator
D.	between condenser and expansion valve
Answer» C. between condenser and evaporator

Discussion

1734.	In a vapour compression system, the condition of refrigerant is dry saturated vapour
A.	before entering the compressor
B.	after leaving the compressor
C.	before entering the condenser
D.	after leaving the condenser
Answer» B. after leaving the compressor

Discussion

1735.	An evaporator is also known as
A.	freezing coil
B.	cooling coil
C.	chilling coil
D.	all of these
Answer» E.

Discussion

1736.	The rate of heat flow through a body is . The term is known as temperature gradient.
A.	Yes
B.	No
Answer» B. No

Discussion

1737.	The highest temperature during the cycle in a vapour compression system occurs after evaporation.
A.	True
B.	False
Answer» C.

Discussion

1738.	If the energy radiated per second per sq. cm. of the surface for wave lengths lying between , and + d is represented by (e .d ), then e is called
A.	absorptive power
B.	emissive power
C.	emissivity
D.	none of these
Answer» C. emissivity

Discussion

1739.	In counter-current flow heat exchangers
A.	both the fluids at inlet are in their hottest state
B.	both the fluids at inlet are in their coldest state
C.	both the fluids at exit are in their hottest state
D.	one fluid is coldest and the other is hottest at inlet
Answer» B. both the fluids at inlet are in their coldest state

Discussion

1740.	The rate of heat flow through a body is . The term x/kA is known as
A.	thermal coefficient
B.	thermal resistance
C.	thermal conductivity
D.	none of these
Answer» C. thermal conductivity

Discussion

1741.	Free convection flow depends on
A.	density
B.	coefficient of viscosity
C.	gravitational force
D.	all of these
Answer» E.

Discussion

1742.	The critical pressure of a liquid is the pressure
A.	above which a liquid will remain a liquid
B.	above which a liquid will explode
C.	above which a liquid will always convert into a vapour
D.	below which a liquid will always be in vapour form
Answer» B. above which a liquid will explode

Discussion

1743.	Conduction is a process of heat transfer
A.	from one particle of the body to another without the actual motion of the particles
B.	from one particle of the body to another by the actual motion of the heated particles.
C.	from a hot body to a cold body, in a straight line, without affecting the intervening medium
D.	none of the above
Answer» B. from one particle of the body to another by the actual motion of the heated particles.

Discussion

1744.	Thermal diffusivity of a substance is
A.	directly proportional to the thermal conductivity
B.	inversely proportional to density of substance
C.	inversely proportional to specific heat
D.	all of the above
Answer» E.

Discussion

1745.	Which of the following refrigerant has the highest freezing point.
A.	Ammonia
B.	Carbon dioxide
C.	Sulphur dioxide
D.	R-12
Answer» C. Sulphur dioxide

Discussion

1746.	Air conditioning means
A.	cooling
B.	heating
C.	dehumidifying
D.	all of these
Answer» E.

Discussion

1747.	A vapour absorption refrigerator uses __________ as a refrigerant.
A.	water
B.	ammonia
C.	freon
D.	aqua-ammonia
Answer» E.

Discussion

1748.	The curved lines on a psychrometric chart indicates
A.	dry bulb temperature
B.	wet bulb temperature
C.	dew point temperature
D.	relative humidity
Answer» E.

Discussion

1749.	During humidification process, __________ increases.
A.	wet bulb temperature
B.	relative humidity
C.	dry bulb temperature
D.	specific humidity
Answer» C. dry bulb temperature

Discussion

1750.	For evaporators and condensers, for the given conditions, the logarithmic mean temperature difference (tm) for parallel flow is __________ that for counter flow.
A.	equal to
B.	less than
C.	greater than
Answer» B. less than

Discussion

Explore topic-wise MCQs in Engineering.

A low wet bulb temperature indicates very __________ humidity.

The critical thickness of insulation is the ratio of thermal conductivity of the insulating material (k) to the heat transfer coefficient at the outer surface of the insulation (h0).

A mixture of dry air and water vapour, when the air has diffused the maximum amount of water vapour into it, is called

The total pressure exerted by the mixture of air and water vapour is equal to the sum of pressures which each constituent would exert, if it occupied the same space by itself. This statement is called

For a given dry bulb temperature, as the relative humidity __________ the wet bulb temperature will increase.

The temperature of air recorded by a thermometer, when the moisture present in it begins to condense, is called wet bulb temperature.

The drier in a refrigeration system removes moisture in the system.

The boiling point of R-12 is about - 30 C.

The material of pipe lines for a system using freon as a refrigerant should be

In a pressure enthalpy chart, the space to the left of the saturated liquid line represents

When the lower temperature of a refrigerating machine is fixed, then the coefficient of performance can be improved by

The refrigerant carbon dioxide is not widely used because of its __________ power require ments per tonne of refrigeration and high operating pressures.

The by-pass factor of a cooling coil decreases with

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

The capacity of the cooling tower and spray ponds __________ as the wet bulb temperature of air decreases.

In counter-current flow heat exchanger, the logarithmic temperature difference between the fluids is __________ as compared to parallel flow heat exchanger.

Dehydration is the process of removing water vapour from the surrounding air.

Environmental protection agencies advice against the use of chloro-fluoro-carbon refrigerants since

The relative coefficient of performance is equal to

The boiling point of carbon dioxide is

The reciprocating refrigerant compressors are very suitable for

The final relative humidity of the air during cooling and dehumidification is generally __________ than that of entering air.

In a pressure enthalpy chart, the space between the saturated liquid line and saturated vapour line, represents sub-cooled liquid region.

Air refrigerator works on

The emissivity of a polished silver body is __________ as compared to black body.

Hydrogen is used in electrolux refrigeration system so as to __________ the rate of evaporation of the liquid ammonia passing through the evaporator.

The wet bulb temperature during sensible cooling of air

In absorption vapour systems, the refrigerant widely used is R-12.

When tc1 and tc2 are the temperatures of cold fluid at entry and exit respectively and th1 and th2 are the temperatures of hot fluid at entry and exit point, and cold fluid has lower heat capacity rate as compared to hot fluid, then effectiveness of the heat exchanger is given by

In larger industrial and commercial reciprocating compression systems, refrigerent widely used is

In a psychrometric chart, specific humidity (moisture content) lines are

The expression Q = AT4 is called

Oil separator in a refrigeration cycle is installed

In a vapour compression system, the condition of refrigerant is dry saturated vapour

An evaporator is also known as

The rate of heat flow through a body is . The term is known as temperature gradient.

The highest temperature during the cycle in a vapour compression system occurs after evaporation.

If the energy radiated per second per sq. cm. of the surface for wave lengths lying between , and + d is represented by (e .d ), then e is called

In counter-current flow heat exchangers

The rate of heat flow through a body is . The term x/kA is known as

Free convection flow depends on

The critical pressure of a liquid is the pressure

Conduction is a process of heat transfer

Thermal diffusivity of a substance is

Which of the following refrigerant has the highest freezing point.

Air conditioning means

A vapour absorption refrigerator uses __________ as a refrigerant.

The curved lines on a psychrometric chart indicates

During humidification process, __________ increases.

For evaporators and condensers, for the given conditions, the logarithmic mean temperature difference (tm) for parallel flow is __________ that for counter flow.