265 + Mcqs in Heat Transfer, Refrigeration and Air Conditioning Page 1 McqOptions

1.	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

2.	The expression is used for calculating
A.	relative humidity
B.	humidity ratio
C.	degree of saturation
D.	pressure of water vapour
Answer» C. degree of saturation

Discussion

3.	The critical thickness of insulation for a sphere is
A.	/
B.	2
C.	/
D.	/
E.	/2
Answer» C. /

Discussion

4.	Planck's law holds good for all coloured bodies.
A.	True
B.	False
Answer» B. False

Discussion

5.	The condition of refrigerant after passing through the condenser in a vapour compression system is
A.	saturated liquid
B.	wet vapour
C.	dry saturated vapour
D.	superheated vapour
Answer» B. wet vapour

Discussion

6.	The difference between dry bulb temperature and dew point temperature, is called
A.	dry bulb depression
B.	wet bulb depression
C.	dew point depression
D.	degree of saturation
Answer» D. degree of saturation

Discussion

7.	Logarithmic mean temperature difference is the same as the arithmetic mean temperature difference.
A.	Agree
B.	Disagree
Answer» C.

Discussion

8.	If the condenser temperature is kept constant, the coefficient of performance of a refrigeration cycle increases with the increase in evaporator temperature.
A.	Yes
B.	No
Answer» B. No

Discussion

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

Discussion

10.	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

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

Discussion

12.	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

13.	Relative humidity is given by (where = Partial pressure of water vapour, = Barometric pressure, = Pressure of saturated air, = Pressure at dry bulb temperature, = Saturation pressure corresponding to wet bulb temperature, and μ = Degree of saturation)
A.	none of these
Answer» C.

Discussion

14.	Kirchhoff's law states that
A.	the total radiation from a black body per second per unit area is directly proportional to the fourth power of the absolute temperature
B.	the wave length corresponding to the maximum energy is proportional to the absolute temperature
C.	the ratio of the emissive power and absorptive power of all bodies is the same and is equal to the emissive power of a perfectly black body
D.	none of the above
Answer» D. none of the above

Discussion

15.	Dew point temperature is the temperature of air recorded by a thermometer, when the moisture present in it begins to condense.
A.	Correct
B.	Incorrect
Answer» B. Incorrect

Discussion

16.	The central air conditioning system has __________ overall efficiency as compared to individual systems.
A.	same
B.	lower
C.	higher
Answer» D.

Discussion

17.	An ordinary passenger aircraft requires a cooling system of capacity.
A.	2 TR
B.	4 TR
C.	8 TR
D.	10 TR
Answer» D. 10 TR

Discussion

18.	The thermal diffusivity for solids is generally less than those for liquids and gases.
A.	True
B.	False
Answer» C.

Discussion

19.	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

20.	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

21.	A device used for transfering heat from one fluid to another is called heat exchanger.
A.	True
B.	False
Answer» B. False

Discussion

22.	The temperature below which a gas is always liquified, is known as critical temperature.
A.	Correct
B.	Incorrect
Answer» C.

Discussion

23.	Conduction is the process of heat transfer from one particle of the body to another by the actual motion of the heated particles.
A.	True
B.	False
Answer» C.

Discussion

24.	During humidification process, dry bulb temperature
A.	remains constant
B.	increases
C.	decreases
Answer» B. increases

Discussion

25.	Fourier's law of heat conduction gives the heat flow for
A.	irregular surfaces
B.	non-uniform temperature surfaces
C.	one dimensional cases only
D.	two dimensional cases only
Answer» D. two dimensional cases only

Discussion

26.	The product of Reynolds number and Prandtl number is known as
A.	Stanton number
B.	Biot number
C.	Peclet number
D.	Grashoff number
Answer» D. Grashoff number

Discussion

27.	The reduced ambient air cooling system has
A.	one cooling turbine and one heat exchanger
B.	one cooling turbine and two heat exchangers
C.	two cooling turbines and one heat exchanger
D.	two cooling turbines and two heat exchangers
Answer» D. two cooling turbines and two heat exchangers

Discussion

28.	The heat of sun reaches to us according to
A.	conduction
B.	convection
C.	radiation
D.	none of these
Answer» D. none of these

Discussion

29.	The specific humidity during humidification process
A.	remains constant
B.	increases
C.	decreases
Answer» C. decreases

Discussion

30.	The boiling point of ammonia is
A.	-10.5°C
B.	-30°C
C.	-33.3°C
D.	-77.7°C
Answer» D. -77.7°C

Discussion

31.	The refrigerant used for absorption refrigerators working on heat from solar collectors is a mixture of water and
A.	carbon dioxide
B.	sulphur dioxide
C.	lithium bromide
D.	R-12
Answer» D. R-12

Discussion

32.	In a black body, all radiations are rejected.
A.	True
B.	False
Answer» C.

Discussion

33.	The absolute humidity is the mass of water vapour present in 1 m of dry air.
A.	Agree
B.	Disagree
Answer» B. Disagree

Discussion

34.	It is desired to condition the outside air from 70% relative humidity and 45° C dry bulb temperature to 50% relative humidity and 25° C dry bulb temperature (room condition). The practical arrangement will be
A.	dehumidification
B.	cooling and humidification
C.	cooling and dehumidification
D.	dehumidification and pure sensible cooling
Answer» D. dehumidification and pure sensible cooling

Discussion

35.	During heating and dehumidification process, dry bulb temperature
A.	remains constant
B.	increases
C.	decreases
Answer» C. decreases

Discussion

36.	A refrigerant compressor is used to
A.	raise the pressure of the refrigerant
B.	raise the temperature of the refrigerant
C.	circulate the refrigerant through the refrigerating system
D.	all of the above
Answer» E.

Discussion

37.	The fluids used in electrolux refrigerator are
A.	water and hydrogen
B.	ammonia and hydrogen
C.	ammonia, water and hydrogen
D.	none of these
Answer» D. none of these

Discussion

38.	The process of undercooling is generally brought about by
A.	circulating more quantity of cooling water through the condenser
B.	using water colder than the main circulating water
C.	employing a heat exchanger
D.	any one of the above
Answer» E.

Discussion

39.	R-12 has the __________ freezing point.
A.	lowest
B.	highest
Answer» B. highest

Discussion

40.	In a vapour absorption refrigeration system, the compressor of the vapour compression system is replaced by
A.	liquid pump
B.	generator
C.	absorber and generator
D.	absorber, generator and liquid pump
Answer» E.

Discussion

41.	The capillary tube, as an expansion device, is used in
A.	domestic refrigerators
B.	water coolers
C.	room air conditioners
D.	all of these
Answer» E.

Discussion

42.	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

43.	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

44.	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

45.	The power per tonne of refrigeration is
A.	3.5/C.O.P.
B.	C.O.P/3.5
C.	3.5 x C.O.P.
D.	none of these
Answer» B. C.O.P/3.5

Discussion

46.	The thermostatic expansion valve is also called
A.	constant pressure valve
B.	constant temperature valve
C.	constant superheat valve
D.	none of these
Answer» D. none of these

Discussion

47.	In figure shown, is a heat engine with efficiency of 0.4 and is a refrigerator. It is given that + = 3. The C.O.P. of the refrigerator is
A.	2.5
B.	3.0
C.	4.0
D.	5.0
Answer» E.

Discussion

48.	A condenser is used in the __________ pressure side of a refrigerating system.
A.	low
B.	high
Answer» C.

Discussion

49.	A steam pipe is to be lined with two layers of insulating materials of different thermal conductivities. For the minimum heat transfer,
A.	the better insulation must be put inside
B.	the better insulation must be put outside
C.	one could place either insulation on either side
D.	one should take into account the steam temperature before deciding as to which insulation is put where
Answer» B. the better insulation must be put outside

Discussion

50.	In a parallel flow heat exchanger, the rate of flow of heat and the rate of decrease of temperature are maximum.
A.	Yes
B.	No
Answer» B. No

Discussion

Explore topic-wise MCQs in Mechanical Engineering.

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 expression is used for calculating

The critical thickness of insulation for a sphere is

Planck's law holds good for all coloured bodies.

The condition of refrigerant after passing through the condenser in a vapour compression system is

The difference between dry bulb temperature and dew point temperature, is called

Logarithmic mean temperature difference is the same as the arithmetic mean temperature difference.

If the condenser temperature is kept constant, the coefficient of performance of a refrigeration cycle increases with the increase in evaporator temperature.

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

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.

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

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

Kirchhoff's law states that

Dew point temperature is the temperature of air recorded by a thermometer, when the moisture present in it begins to condense.

The central air conditioning system has __________ overall efficiency as compared to individual systems.

An ordinary passenger aircraft requires a cooling system of capacity.

The thermal diffusivity for solids is generally less than those for liquids and gases.

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

A device used for transfering heat from one fluid to another is called heat exchanger.

The temperature below which a gas is always liquified, is known as critical temperature.

Conduction is the process of heat transfer from one particle of the body to another by the actual motion of the heated particles.

During humidification process, dry bulb temperature

Fourier's law of heat conduction gives the heat flow for

The product of Reynolds number and Prandtl number is known as

The reduced ambient air cooling system has

The heat of sun reaches to us according to

The specific humidity during humidification process

The boiling point of ammonia is

The refrigerant used for absorption refrigerators working on heat from solar collectors is a mixture of water and

In a black body, all radiations are rejected.

The absolute humidity is the mass of water vapour present in 1 m of dry air.

It is desired to condition the outside air from 70% relative humidity and 45° C dry bulb temperature to 50% relative humidity and 25° C dry bulb temperature (room condition). The practical arrangement will be

During heating and dehumidification process, dry bulb temperature

A refrigerant compressor is used to

The fluids used in electrolux refrigerator are

The process of undercooling is generally brought about by

R-12 has the __________ freezing point.

In a vapour absorption refrigeration system, the compressor of the vapour compression system is replaced by

The capillary tube, as an expansion device, is used in

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

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

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

The power per tonne of refrigeration is

The thermostatic expansion valve is also called

In figure shown, is a heat engine with efficiency of 0.4 and is a refrigerator. It is given that + = 3. The C.O.P. of the refrigerator is

A condenser is used in the __________ pressure side of a refrigerating system.

A steam pipe is to be lined with two layers of insulating materials of different thermal conductivities. For the minimum heat transfer,

In a parallel flow heat exchanger, the rate of flow of heat and the rate of decrease of temperature are maximum.