Mechanical Engineering - Heat Transfer, Refrigeration and Air Conditioning Quiz (or) MCQ

1 .

The centrifugal compressors are generally used for refrigerants that require

A)

large displacements and low condensing pressures

B)

large displacements and high condensing pressures

C)

small displacements and high condensing pressures

D)

small displacements and low condensing pressures

Correct Answer : large displacements and low condensing pressures

2 .

The automobile radiator is a heat exchanger of

A)

parallel flow type

B)

regenerator type

C)

cross flow type

D)

counter flow type

Correct Answer : cross flow type

3 .

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

Correct Answer : 4 kW

4 .

The wet bulb temperature during sensible heating of air

A)

increases

B)

decreases

C)

remains constant

D)

None of the above

Correct Answer : increases

5 .

Which of the following statement is wrong?

A)

The heat transfer in liquid and gases takes place according to convection.

B)

The thermal conductivity of solid metals increases with rise in temperature,

C)

The amount of heat flow through a body is dependent upon the material of the body.

D)

Logarithmic mean temperature difference is not equal to the arithmetic mean temperature difference.

Correct Answer : The thermal conductivity of solid metals increases with rise in temperature,

6 .

In free convection heat transfer transition from laminar to turbulent flow is governed by the critical value of the

A)

Reynold's number

B)

Grashoff's number

C)

Prandtl number, Grashoff's number

D)

Reynold's number, Grashoff's number

Correct Answer : Prandtl number, Grashoff's number

7 .

In a refrigerating machine, heat rejected is __________ heat absorbed.

A)

less than

B)

equal to

C)

greater than

D)

None of the above

Correct Answer : greater than

8 .

The humidity ratio or specific humidity is the mass of water vapour present in

A)

1 kg of wet air

B)

1 kg of dry air

C)

1 mÂ³ of wet air

D)

1 mÂ³ of dry air

Correct Answer : 1 kg of dry air

9 .

The formation of frost on cooling coils in a refrigerator

A)

increases heat transfer

B)

reduces power consumption

C)

improves C.O.P. of the system

D)

increases power consumption

Correct Answer : increases power consumption

10 .

The most commonly used method for the design of duct size is the

A)

static regain method

B)

equal friction method

C)

dual or double method

D)

velocity reduction method

Correct Answer : static regain method

11 .

In counter-current flow heat exchangers

A)

one fluid is coldest and the other is hottest at inlet

B)

both the fluids at inlet are in their hottest state

C)

both the fluids at exit are in their hottest state

D)

both the fluids at inlet are in their coldest state

Correct Answer : both the fluids at inlet are in their hottest state

12 .

Stefan-Boltzmann law is applicable for heat transfer by convection.

A)

Agree

B)

Disagree

C)

Can Not Say

D)

None of the above

Correct Answer : Disagree

13 .

The difference between dry bulb temperature and wet bulb temperature, is called

A)

degree of saturation

B)

dry bulb depression

C)

wet bulb depression

D)

dew point depression

Correct Answer : wet bulb depression

14 .

The by-pass factor for a cooling coil

A)

decreases with increase in velocity of air passing through it

B)

remains unchanged with increase in velocity of air passing through it

C)

Both (A) and (B)

D)

increases with increase in velocity of air passing through it

Correct Answer : increases with increase in velocity of air passing through it

15 .

The curved lines on a psychrometric chart indicates

A)

relative humidity

B)

dry bulb temperature

C)

wet bulb temperature

D)

dew point temperature

Correct Answer : relative humidity

16 .

The freon group of refrigerants are

A)

inorganic refrigerants

B)

azeotrope refrigerants

C)

halo-carbon refrigerants

D)

hydro-carbon refrigerants

Correct Answer : halo-carbon refrigerants

17 .

A pressure gauge on the discharge side of a refrigerant compressor reads too high. The reasons will be

A)

lack of cooling water

B)

dirty condenser surface

C)

water temperature being high

D)

All of the above

Correct Answer : All of the above

18 .

During humidification process, __________ increases.

A)

specific humidity

B)

relative humidity

C)

dry bulb temperature

D)

wet bulb temperature

Correct Answer : relative humidity

19 .

The heat transfer from a hot body to a cold body is directly proportional to the surface area and difference of temperatures between the two bodies. This statement is called

A)

Newton's law of cooling

B)

Stefan's law

C)

Newton's law of heating

D)

First law of thermodynamics

Correct Answer : Newton's law of cooling

20 .

The pressure at the inlet of a refrigerant compressor is called

A)

back pressure

B)

suction pressure

C)

critical pressure

D)

discharge pressure

Correct Answer : suction pressure

21 .

The lowest temperature during the cycle in a vapour compression system occurs after

A)

expansion

B)

compression

C)

evaporation

D)

condensation

Correct Answer : evaporation

22 .

The process, generally used in summer air conditioning to cool and dehumidify the air, is called

A)

humidification

B)

dehumidification

C)

heating and humidification

D)

cooling and dehumidification

Correct Answer : cooling and dehumidification

23 .

The leakage in a refrigeration system using ammonia is detected by

A)

halide torch

B)

soap and water

C)

sulphur sticks

D)

All of the above

Correct Answer : sulphur sticks

24 .

The temperature of air recorded by a thermometer, when its bulb is surrounded by a wet cloth exposed to the air, is called

A)

wet bulb temperature

B)

dry bulb temperature

C)

dew point temperature

D)

None of the above

Correct Answer : wet bulb temperature

25 .

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

A)

emissivity

B)

emissive power

C)

absorptive power

D)

None of the above

Correct Answer : emissive power

26 .

R-12 is generally preferred over R-22 in deep freezers since

A)

it has low operating pressures

B)

it gives higher coefficient of performance

C)

it is miscible with oil over large range of temperatures

D)

All of the above

Correct Answer : it is miscible with oil over large range of temperatures

27 .

An infinite parallel planes with emissivities eâ‚ and eâ‚‚, the interchange factor for radiation from surface 1 to surface 2 is given by

A)

eâ‚ eâ‚‚ / eâ‚ + eâ‚‚ - eâ‚ eâ‚‚

B)

1/eâ‚ + 1/ eâ‚‚

C)

eâ‚ + eâ‚‚

D)

eâ‚ eâ‚‚

Correct Answer : eâ‚ eâ‚‚ / eâ‚ + eâ‚‚ - eâ‚ eâ‚‚

28 .

The atmospheric air at dry bulb temperature of 15°C enters a heating coil maintained at 40°C. The air leaves the heating coil at 25°C. The by-pass factor of the heating coil is

A)

0.67

B)

0.6

C)

0.4

D)

0.376

Correct Answer : 0.6

29 .

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

A)

the moisture present in it begins to condense

B)

it is not affected by the moisture present in the air

C)

its bulb is surrounded by a wet cloth exposed to the air

D)

None of the above

Correct Answer : it is not affected by the moisture present in the air

30 .

A valve which maintains a constant degree of superheat at the end of the evaporator coil, is called

A)

high side float valve

B)

automatic expansion valve

C)

thermostatic expansion valve

D)

Correct Answer : low side float valve

31 .

In a spray washing system, if the temperature of water is higher than the dry bulb temperature of entering air, then the air is

A)

heated and humidified

B)

cooled and humidified

C)

cooled and dehumidified

D)

heated and dehumidified

Correct Answer : heated and humidified

32 .

Which of the following refrigerant has the maximum ozone depletion potential in the stratophere?

A)

Flourine

B)

Ammonia

C)

Carbon dioxide

D)

Sulphur dioxide

Correct Answer : Flourine

33 .

Which of the following statement is correct?

A)

The wet bulb temperature is a measure of enthalpy of moist air.

B)

The constant enthalpy lines are also constant wet bulb temperature lines.

C)

The wet bulb and dry bulb temperature are equal at saturation condition.

D)

All of the above

Correct Answer : All of the above

34 .

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

Correct Answer : Three

35 .

In electrolux refrigerator

A)

ammonia is absorbed in water

B)

ammonia evaporates in hydrogen

C)

ammonia is absorbed in hydrogen

D)

hydrogen evaporates in ammonia

Correct Answer : ammonia evaporates in hydrogen

36 .

The specific humidity during heating and humidification process.

A)

increases

B)

decreases

C)

remains constant

D)

None of the above

Correct Answer : increases

37 .

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

A)

30 bar

B)

15 bar

C)

8 bar

D)

2 bar

Correct Answer : 8 bar

38 .

A boot-strap air cooling system has

A)

one heat exchanger

B)

two heat exchangers

C)

three heat exchangers

D)

four heat exchangers

Correct Answer : two heat exchangers

39 .

The boiling point of __________ is -10.5Â°C.

A)

R-12

B)

ammonia

C)

carbon dioxide

D)

sulphur dioxide

Correct Answer : sulphur dioxide

40 .

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

Correct Answer : 210 kJ/min

41 .

A condenser of refrigeration system rejects heat at the rate of 120 kW, while its compressor consumes a power of 30 kW. The coefficient of performance of the system will be

A)

1/4

B)

1/3

C)

3

D)

4

Correct Answer : 4

42 .

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

A)

condenser

B)

absorber

C)

evaporator

D)

None of the above

Correct Answer : condenser

43 .

In a shell and tube heat exchanger, baffles are provided on the shell side to

A)

improve heat transfer

B)

provide support for tubes

C)

prevent stagnation of shell side fluid

D)

All of the above

Correct Answer : All of the above

44 .

A refrigerant with the highest critical pressure is

A)

R-11

B)

R-12

C)

R-22

D)

Ammonia

Correct Answer : Ammonia

45 .

The boiling point of ammonia is

A)

-10.5Â°C

B)

-30Â°C

C)

-33.3Â°C

D)

-77.7Â°C

Correct Answer : -33.3Â°C

46 .

Most air cooled condensers are designed to operate with a temperature difference of

A)

5Â°C

B)

8Â°C

C)

14Â°C

D)

22Â°C

Correct Answer : 14Â°C

47 .

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

A)

R-12

B)

lithium bromide

C)

carbon dioxide

D)

sulphur dioxide

Correct Answer : lithium bromide

48 .

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

A)

constant pressure expansion process

B)

isentropic expansion process

C)

isentropic compression process

D)

constant pressure cooling process

Correct Answer : constant pressure expansion process

49 .

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

A)

the moisture present in it begins to condense

B)

it is not effected by the moisture present in the air

C)

its bulb is surrounded by a wet cloth exposed to the air

D)

None of the above

Correct Answer : its bulb is surrounded by a wet cloth exposed to the air

50 .

The coefficient of performance (C.O.P.) of a refrigerator working as a heat pump is given by

A)

(C.O.P)_P = (C.O.P)_R

B)

(C.O.P.)_P = (C.O.P.)_R + 1

C)

(C.O.P)_P = (C.O.P)_R - 1

D)

(C.O.P.)_P = (C.O.P.)_R + 2

Correct Answer : (C.O.P.)_P = (C.O.P.)_R + 1

51 .

The comfort conditions in air conditioning are at (where DBT = Dry bulb temperature, and RH = Relative humidity)

A)

20Â°C DBT and 80% RH

B)

22Â°C DBT and 60% RH

C)

25Â°C DBT and 40% RH

D)

25Â°C DBT and 100% RH

Correct Answer : 22Â°C DBT and 60% RH

52 .

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

A)

True

B)

False

C)

Can Not Say

D)

None of the above

Correct Answer : False

53 .

The pressure at the outlet of a refrigerant compressor is called

A)

back pressure

B)

critical pressure

C)

suction pressure

D)

discharge pressure

Correct Answer : discharge pressure

54 .

The dry bulb temperature lines, on the psychrometric chart are

A)

vertical and uniformly spaced

B)

horizontal and uniformly spaced

C)

curved lines

D)

horizontal and non-uniformly spaced

Correct Answer : vertical and uniformly spaced

55 .

In a psychrometric chart, dew point temperature lines are horizontal and non-uniformly spaced.

A)

Correct

B)

Incorrect

C)

Can Not Say

D)

None of the above

Correct Answer : Correct

56 .

The evaporator used in house-hold refrigerators is

A)

defrosting evaporator

B)

non-frosting evaporator

C)

frosting evaporator

D)

None of the above

Correct Answer : frosting evaporator

57 .

The __________ point of ammonia is -77.7Â°C.

A)

boiling

B)

freezing

C)

Can Not Say

D)

None of the above

Correct Answer : freezing

58 .

The lowest thermal diffusivity is of

A)

iron

B)

lead

C)

rubber

D)

aluminium

Correct Answer : rubber

59 .

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

A)

increases

B)

decreases

C)

Can Not Say

D)

None of the above

Correct Answer : decreases

60 .

According to Dalton's law of partial pressures, (where p_b = Barometric pressure, p_a = Partial pressure of dry air, and p_v = Partial pressure of water vapour)

A)

P_b = p_a + p_v

B)

P_b = p_a/p_v

C)

P_b = p_a - p_v

D)

P_b = p_a x p_v

Correct Answer : P_b = p_a + p_v

61 .

The relative humidity is defined as

A)

the mass of water vapour present in 1 kg of dry air

B)

the mass of water vapour present in 1 mÂ³ of dry air

C)

the ratio of the actual mass of water vapour in a unit mass of dry air to the mass of water vapour in the same mass of dry air when it is saturated at the same temperature and pressure.

D)

the ratio of actual mass of water vapour in a given volume of moist air to the mass of water vapour in the same volume of saturated air at the same temperature and pressure

Correct Answer : the ratio of actual mass of water vapour in a given volume of moist air to the mass of water vapour in the same volume of saturated air at the same temperature and pressure

62 .

In aqua-ammonia and Lithium-bromide water absorption refrigeration systems, the refrigerants are respectively

A)

ammonia and water

B)

water and water

C)

water and lithium bromide

D)

ammonia and lithium bromide

Correct Answer : ammonia and water

63 .

The optimum effective temperature for human comfort is

A)

lower in winter than in summer

B)

same in winter and summer

C)

higher in winter than in summer

D)

not dependent on season

Correct Answer : lower in winter than in summer

64 .

As relative humidity decreases, the dew point temperature will be __________ wet bulb temperature.

A)

same as

B)

lower than

C)

higher man

D)

None of the above

Correct Answer : lower than

65 .

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

A)

after leaving the condenser

B)

after leaving the compressor

C)

before entering the compressor

D)

before entering the condenser

Correct Answer : before entering the compressor

66 .

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

A)

R-12

B)

carbon dioxide

C)

sulphur dioxide

D)

ammonia

Correct Answer : ammonia

67 .

An evaporator is also known as

A)

cooling coil

B)

chilling coil

C)

freezing coil

D)

All of the above

Correct Answer : All of the above

68 .

Oil separator in a refrigeration cycle is installed

A)

between compressor and condenser

B)

before compressor

C)

between condenser and evaporator

D)

between condenser and expansion valve

Correct Answer : between compressor and condenser

69 .

During sensible cooling of air, specific humidity

A)

increases

B)

remains constant

C)

decreases

D)

None of the above

Correct Answer : remains constant

70 .

The expression Q = ρ ATâ´ is called

A)

Fourier equation

B)

Joseph-Stefan equation

C)

Stefan-Boltzmann equation

D)

Newton-Rikhmann equation

Correct Answer : Stefan-Boltzmann equation

71 .

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

A)

curved lines

B)

horizontal and uniformly spaced

C)

vertical and uniformly spaced

D)

horizontal and non-uniformly spaced

Correct Answer : horizontal and uniformly spaced

72 .

The transfer of heat by molecular collision is known as

A)

radiation

B)

convection

C)

conduction

D)

None of the above

Correct Answer : conduction

73 .

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

A)

equal to

B)

less than

C)

greater than

D)

None of the above

Correct Answer : equal to

74 .

A vapour absorption refrigerator uses __________ as a refrigerant.

A)

freon

B)

water

C)

ammonia

D)

aqua-ammonia

Correct Answer : aqua-ammonia

75 .

Which of the following refrigerant has the highest freezing point.

A)

R-12

B)

Carbon dioxide

C)

Ammonia

D)

Sulphur dioxide

Correct Answer : Carbon dioxide

76 .

The ratio of the thickness of thermal boundary layer to the thickness of hydrodynamic boundary layer is equal to (Prandtl number)ⁿ, where n is equal to

A)

1

B)

-1/3

C)

-2/3

D)

-1

Correct Answer : -1/3

77 .

Which of the following would lead to a reduction in thermal resistance?

A)

In convection, stirring of the fluid and cleaning the heating surface.

B)

In radiation, increasing the temperature and reducing the emissivity.

C)

In conduction, reduction in the thickness of the material and an increase in thermal conductivity.

D)

All of the above

Correct Answer : All of the above

78 .

Air conditioning means

A)

cooling

B)

heating

C)

dehumidifying

D)

All of the above

Correct Answer : All of the above

79 .

The emissivity for a black body is

A)

1

B)

0

C)

0.5

D)

0.75

Correct Answer : 1

80 .

The temperature of air recorded by a thermometer, when it is not effected by the moisture present in the air, is called

A)

dew point temperature

B)

wet bulb temperature

C)

dry bulb temperature

D)

None of the above

Correct Answer : dry bulb temperature

81 .

A human body feels comfortable when the heat produced by the metabolism of human body is equal to the

A)

heat dissipated to the surroundings

B)

heat stored in the human body

C)

Sum of (A) and (B)

D)

Difference of (A) and (B)

Correct Answer : Sum of (A) and (B)

82 .

During sensible cooling,

A)

specific humidity increases

B)

wet bulb temperature increases

C)

relative humidity remains constant

D)

partial pressure of vapour remains constant

Correct Answer : partial pressure of vapour remains constant

83 .

The process of heat transfer from one particle of the body to another by the actual motion of the heated particles, is called

A)

radiation

B)

convection

C)

conduction

D)

None of the above

Correct Answer : convection

84 .

In a domestic refrigerator, a capillary tube controls the flow of refrigerant from the

A)

evaporator to the thermostat

B)

condenser to the expansion valve

C)

expansion valve to the evaporator

D)

condenser to the evaporator

Correct Answer : condenser to the evaporator

85 .

In a lithium bromide absorption refrigeration system

A)

water is used as a refrigerant and lithium bromide as an absorbent

B)

lithium bromide is used as a refrigerant and water as an absorbent

C)

ammonia is used as a refrigerant and lithium bromide as an absorbent

D)

None of the above

Correct Answer : water is used as a refrigerant and lithium bromide as an absorbent

86 .

The refrigerant used in small-tonnage commercial machines (hermetically sealed units) is

A)

R-12

B)

ammonia

C)

sulphur dioxide

D)

carbon dioxide

Correct Answer : sulphur dioxide

87 .

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

A)

generator

B)

liquid pump

C)

absorber and generator

D)

absorber, generator and liquid pump

Correct Answer : absorber, generator and liquid pump

88 .

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

Correct Answer : the better insulation must be put inside

89 .

When the air is passed through an insulated chamber having sprays of water maintained at a temperature higher than the dew point temperature of entering air but lower than its dry bulb temperature, then the air is said to be

A)

heated and humidified

B)

cooled and humidified

C)

cooled and dehumidified

D)

heated and dehumidified

Correct Answer : cooled and humidified

90 .

Which of the following statement is wrong?

A)

In vapour compression cycle, the useful part of the heat transfer is at the condenser.

B)

In ammonia-hydrogen (electolux) refrigerator, no compressor, pump or fan is required.

C)

The performance of the vapour compression refrigerator varies considerably with both vaporising and condensing temperatures.

D)

The effect of under-cooling the liquid refrigerant is to decrease the coefficient of performance.

Correct Answer : The effect of under-cooling the liquid refrigerant is to decrease the coefficient of performance.

91 .

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

A)

low

B)

high

C)

same

D)

very low

Correct Answer : very low

92 .

The ratio of heat extracted in the refrigerator to the workdone on the refrigerant is called

A)

refrigerating efficiency

B)

relative coefficient of performance

C)

coefficient of performance of refrigeration

D)

coefficient of performance of heat pump

Correct Answer : coefficient of performance of refrigeration

93 .

The superheated vapour region, in a pressure enthalpy chart, is represented by the space

A)

to the left of saturated liquid line

B)

to the right of saturated liquid line

C)

between the saturated liquid line and saturated vapour line

D)

None of the above

Correct Answer : between the saturated liquid line and saturated vapour line

94 .

The alignment circle is marked on the psychrometric chart at

A)

20Â°C DBT and 50% RH

B)

26Â°C DBT and 50% RH

C)

20Â°C DBT and 60% RH

D)

26Â°C DBT and 60% RH

Correct Answer : 26Â°C DBT and 50% RH

95 .

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

A)

wet bulb temperature of air

B)

ambient air temperature

C)

dry bulb temperature of air

D)

dew point temperature of air

Correct Answer : wet bulb temperature of air

96 .

The ratio of Nusselt number and the product of Reynold's number and Prandtl number is equal to

A)

Biot number

B)

Stanton number

C)

Peclet number

D)

Grashoff number

Correct Answer : Stanton number

97 .

The index which corelates the combined effects of air temperature, relative humidity and air velocity on the human body, is known as

A)

dew point temperature

B)

mean radiant temperature

C)

Both (A) and (B)

D)

effective temperature

Correct Answer : effective temperature

98 .

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

A)

lower

B)

same

C)

higher

D)

None of the above

Correct Answer : higher

99 .

Which of the following statement is correct?

A)

The human body can lose heat even if its temperature is less than the atmospheric temperature.

B)

The increase in air movement increases the evaporation from the human body.

C)

The warm air increases the rate of radiation of heat from the human body.

D)

Both (A) and (B)

Correct Answer : Both (A) and (B)

100 .

The thermostatic expansion valve is used in __________ type of evaporators.

A)

dry

B)

DX coil

C)

flooded

D)

None of the above

Correct Answer : dry

101 .

When the temperature of the surrounding is higher than the temperature of the body, then the heat loss by convection from the body to the surrounding will be

A)

zero

B)

negative

C)

positive

D)

None of the above

Correct Answer : negative

102 .

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

A)

Biot number

B)

Prandtl number

C)

Stanton number

D)

Grashoff number

Correct Answer : Biot number

103 .

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

C)

Can Not Say

D)

None of the above

Correct Answer : Correct

104 .

Kirchhoff's law states that

A)

the wave length corresponding to the maximum energy is proportional to the absolute temperature

B)

the total radiation from a black body per second per unit area is directly proportional to the fourth power of 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

Correct Answer : 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

105 .

The critical thickness of insulation for a sphere is

A)

hâ‚€/k

B)

hâ‚€/2k

C)

k/hâ‚€

D)

2k/hâ‚€

Correct Answer : 2k/hâ‚€

106 .

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

A)

dry bulb depression

B)

dew point depression

C)

wet bulb depression

D)

degree of saturation

Correct Answer : dew point depression

107 .

Film coefficient is defined as the ratio of

A)

thickness of film of fluid to the thermal conductivity

B)

thermal conductivity to the equivalent thickness of the film of fluid

C)

thickness of film of fluid to the temperature drop through the films of fluids

D)

temperature drop through the films of fluids to the thickness of film of fluids

Correct Answer : thermal conductivity to the equivalent thickness of the film of fluid

108 .

The operating temperature of a cold storage is - 2° C. The heat leakage from the surrounding is 30 kW for the ambient temperature of 40° C. The actual C.O.P. of refrigeration plant used is one fourth that of ideal plant working between the same temperatures. The power required to drive the plant is

A)

1.86 kW

B)

3.72 kW

C)

7.44 kW

D)

18.6 kW

Correct Answer : 18.6 kW

109 .

The air cooling system mostly used in transport type aircrafts is

A)

boot-strap air cooling system

B)

simple air cooling system

C)

simple evaporative air cooling system

D)

All of the above

Correct Answer : boot-strap air cooling system

110 .

A one tonne refrigerating machine means that

A)

one tonne refrigerant is used

B)

one tonne is the total mass of machine

C)

one tonne of water can be converted into ice

D)

one tonne of ice when melts from and at 0Â° C in 24 hours, the refrigeration effect is equivalent to 210 kJ/min

Correct Answer : one tonne of ice when melts from and at 0Â° C in 24 hours, the refrigeration effect is equivalent to 210 kJ/min

111 .

In chemical dehumidification process,

A)

dry bulb temperature increases

B)

wet bulb temperature decreases

C)

dew point temperature decreases

D)

All of the above

Correct Answer : All of the above

112 .

Thermal diffusivity is a

A)

function of temperature

B)

dimensionless parameter

C)

physical property of a substance

D)

All of the above

Correct Answer : physical property of a substance

113 .

The total radiation from a black body per second per unit area is __________ fourth power of the absolute temperature. This statement is known as Stefan-Boltzmann law.

A)

equal to

B)

directly proportional to

C)

inversely proportional to

D)

All of the above

Correct Answer : directly proportional to

114 .

Thermal conductivity of solid metals __________ with rise in temperature.

A)

decreases

B)

increases

C)

remains same

D)

None of the above

Correct Answer : decreases

115 .

The unit of Stefan-Boltzmann constant is

A)

Watt/mK

B)

Watt/m²Kâ´

C)

Watt/mK²

D)

Watt/m²K²

Correct Answer : Watt/m²Kâ´

116 .

The horizontal and non-uniformly spaced lines on a psychrometric chart indicates

A)

specific humidity

B)

dew point temperature

C)

dry bulb temperature

D)

wet bulb temperature

Correct Answer : dew point temperature

117 .

Which of the following refrigerant is highly toxic and flammable?

A)

R-12

B)

Carbon dioxide

C)

Ammonia

D)

Sulphur dioxide

Correct Answer : Ammonia

118 .

A reversible engine has ideal thermal efficiency of 30%. When it is used as a refrigerating machine with all other conditions unchanged, the coefficient of performance will be

A)

2.33

B)

3.33

C)

4.33

D)

5.33

Correct Answer : 2.33

119 .

In a psychrometric process, the sensible heat added is 30 kJ/s and the latent heat added is 20 kJ/s. The sensible heat factor for the process will be

A)

1.5

B)

0.67

C)

0.6

D)

0.3

Correct Answer : 0.6

120 .

The highest thermal diffusivity is of

A)

iron

B)

lead

C)

wood

D)

concrete

Correct Answer : lead

121 .

The amount of radiation mainly depends upon the

A)

nature of the body

B)

temperature of the body

C)

type of surface of the body

D)

All of the above

Correct Answer : All of the above

122 .

For ammonia refrigerating systems, the tubes of a shell and tube condenser are made of

A)

steel

B)

brass

C)

copper

D)

aluminium

Correct Answer : steel

123 .

The emissive power of a body depends upon its

A)

wave length

B)

temperature

C)

physical nature

D)

All of the above

Correct Answer : All of the above

124 .

An electric cable of aluminium conductor (k = 240 W/mK) is to be insulated with rubber (k = 0.15 W/mK). The cable is to be located in air (h = 6 W/m²). The critical thickness of insulation will be

A)

25 mm

B)

40 mm

C)

160 mm

D)

800 mm

Correct Answer : 25 mm

125 .

The vertical and uniformly spaced lines on a psychrometric chart indicates

A)

specific humidity

B)

wet bulb temperature

C)

dry bulb temperature

D)

dew point temperature

Correct Answer : dry bulb temperature

126 .

The dehumidification process, on the psychrometric chart, is shown by

A)

curved line

B)

vertical line

C)

inclined line

D)

horizontal Sine

Correct Answer : vertical line

127 .

In case of sensible heating of air, the coil efficiency is given by (where B.P.F. = By-pass factor)

A)

1 - B.P.F.

B)

1 + B.RF.

C)

B.P.F. - 1

D)

None of the above

Correct Answer : 1 - B.P.F.

128 .

The coefficient of performance (C.O.P.) is the reciprocal of the efficiency of a heat engine.

A)

True

B)

False

C)

Can Not Say

D)

None of the above

Correct Answer : True

129 .

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

A)

emissivity

B)

emissive power

C)

Both (A) and (B)

D)

absorptive power

Correct Answer : absorptive power

130 .

The wet bulb temperature at 100% relative humidity is __________ dry bulb temperature.

A)

same as

B)

lower than

C)

higher than

D)

None of the above

Correct Answer : same as

131 .

The freezing point of sulphur dioxide is

A)

-56.6Â°C

B)

-75.2Â°C

C)

-77.7Â°C

D)

-135.8Â°C

Correct Answer : -75.2Â°C

132 .

Free convection flow depends on

A)

density

B)

gravitational force

C)

coefficient of viscosity

D)

All of the above

Correct Answer : All of the above

133 .

Conduction is a process of heat transfer

A)

from one particle of the body to another by the actual motion of the heated particles

B)

from a hot body to a cold body, in a straight line, without affecting the intervening medium

C)

from one particle of the body to another without the actual motion of the particles

D)

None of the above

Correct Answer : from one particle of the body to another without the actual motion of the particles

134 .

Thermal diffusivity of a substance is

A)

inversely proportional to specific heat

B)

inversely proportional to density of substance

C)

directly proportional to the thermal conductivity

D)

All of the above

Correct Answer : All of the above

135 .

The critical pressure of a liquid is the pressure

A)

above which a liquid will explode

B)

above which a liquid will remain a liquid

C)

above which a liquid will always convert into a vapour

D)

below which a liquid will always be in vapour form

Correct Answer : above which a liquid will remain a liquid

136 .

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

Correct Answer : cooling and dehumidification

137 .

During heating and dehumidification process, dry bulb temperature

A)

increases

B)

decreases

C)

remains constant

D)

None of the above

Correct Answer : increases

138 .

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

Correct Answer : All of the above

139 .

In which of the following refrigeration system, waste heat can be effectively used?

A)

Air refrigeration cycle

B)

Vapour compression cycle

C)

Vapour absorption cycle

D)

None of the above

Correct Answer : Vapour absorption cycle

140 .

R-12 has the __________ freezing point.

A)

lowest

B)

highest

C)

Can Not Say

D)

None of the above

Correct Answer : lowest

141 .

The refrigerant after condensation process is cooled below the saturation temperature before throttling. Such a process is called

A)

super-cooling

B)

normal cooling

C)

sub-cooling or under-cooling

D)

None of the above

Correct Answer : sub-cooling or under-cooling

142 .

During heating and humidification, the final relative humidity of air

A)

is lower than that of the entering air

B)

is higher than that of the entering air

C)

can be lower or higher than that of the entering air

D)

None of the above

Correct Answer : can be lower or higher than that of the entering air

143 .

The process of undercooling is generally brought about by

A)

employing a heat exchanger

B)

using water colder than the main circulating water

C)

circulating more quantity of cooling water through the condenser

D)

Any one of the above

Correct Answer : Any one of the above

144 .

The fluids used in electrolux refrigerator are

A)

water and hydrogen

B)

ammonia, water and hydrogen

C)

ammonia and hydrogen

D)

None of the above

Correct Answer : ammonia, water and hydrogen

145 .

Air refrigerator works on

A)

Bell Coleman cycle

B)

reversed Carnot cycle

C)

Both (A) and (B)

D)

None of the above

Correct Answer : Both (A) and (B)

146 .

The boiling point of carbon dioxide is

A)

-20.5Â°C

B)

-50Â°C

C)

-63.3Â°C

D)

-78.3Â°C

Correct Answer : -78.3Â°C

147 .

The reciprocating refrigerant compressors are very suitable for

A)

small displacements and high condensing pressures

B)

small displacements and low condensing pressures

C)

large displacements and low condensing pressures

D)

large displacements and high condensing pressures

Correct Answer : small displacements and high condensing pressures

148 .

The cooling system used for supersonic aircrafts and rockets is

A)

simple air cooling system

B)

regenerative air cooling system

C)

boot-strap air cooling system

D)

reduced ambient air cooling system

Correct Answer : regenerative air cooling system

149 .

Which of the following statement is correct?

A)

In vapour absorption refrigerator, the compression of refrigerent is avoided.

B)

Sub-cooling can be achieved by circulating more quantity of cooling water through the condenser.

C)

In vapour compression refrigeration, the vapour is drawn in the compressor cylinder during its suction stroke and is compressed adiabatically during the compression stroke.

D)

All of the above

Correct Answer : All of the above

150 .

The colour of the flame of halide torch, in case of leakage of freon refrigerant, will change to

A)

red

B)

yellow

C)

bright green

D)

orange

Correct Answer : bright green

151 .

The humidification process, on the psychrometric chart is shown by

A)

curved line

B)

vertical line

C)

inclined line

D)

horizontal line

Correct Answer : vertical line

152 .

The desirable property of a refrigerant is

A)

low boiling point

B)

high critical temperature

C)

high latent heat of vaporisation

D)

All of the above

Correct Answer : All of the above

153 .

In a boot-strap air evaporative cooling system, the evaporator is provided

A)

between the second heat exchanger and the cooling turbine

B)

between the combustion chamber and the first heat exchanger

C)

between the first heat exchanger and the secondary compressor

D)

between the secondary compressor and the second heat exchanger

Correct Answer : between the second heat exchanger and the cooling turbine

154 .

The thermal diffusivity for gases is generally __________ those for liquids.

A)

equal to

B)

less than

C)

greater than

D)

None of the above

Correct Answer : greater than

155 .

A good refrigerant should have

A)

low C.O.P. and low freezing point

B)

high operating pressures and low freezing point

C)

high specific volume and high latent heat of vaporisation

D)

high latent heat of vaporisation and low freezing point

Correct Answer : high latent heat of vaporisation and low freezing point

156 .

According to Stefan-Boltzmann law, the total radiation from a black body per second per unit area is directly proportional to the

A)

absolute temperature

B)

fourth power of the absolute temperature

C)

cube of the absolute temperature

D)

square of the absolute temperature

Correct Answer : fourth power of the absolute temperature

157 .

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

A)

these react with ozone layer

B)

these react with oxygen and cause its depletion

C)

these react with water vapour and cause acid rain

D)

these react with plants and cause green-house effect

Correct Answer : these react with ozone layer

158 .

The by-pass factor of a cooling coil decreases with

A)

increase in fin spacing and increase in number of rows

B)

decrease 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

Correct Answer : decrease in fin spacing and increase in number of rows

159 .

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

A)

raising the higher temperature

B)

operating the machine at lower speeds

C)

lowering the higher temperature

D)

operating the machine at higher speeds

Correct Answer : lowering the higher temperature

160 .

While designing the refrigeration system of an aircraft, the prime consideration is that the

A)

power per TR is low

B)

system has high C.O.P.

C)

mass of the refrigeration equipment is low

D)

mass of refrigerant circulated in the system is low

Correct Answer : mass of the refrigeration equipment is low

161 .

The heat transfer takes place according to

A)

Kirchhoff's law

B)

First law of thermodynamics

C)

Zeroth law of thermodynamics

D)

Second law of thermodynamics

Correct Answer : Second law of thermodynamics

162 .

An electrolux refrigerator is called a __________ absorption system.

A)

single fluid

B)

two fluids

C)

three fluids

D)

None of the above

Correct Answer : three fluids

163 .

Thermal conductivity of water __________ with rise in temperature.

A)

increases

B)

decreases

C)

remains same

D)

may increase or decrease depending upon temperature

Correct Answer : may increase or decrease depending upon temperature

164 .

The coefficient of performance of a domestic refrigerator is __________ as compared to a domestic air-conditioner.

A)

less

B)

same

C)

more

D)

None of the above

Correct Answer : less

165 .

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

Correct Answer : do not move actually

166 .

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)

lower

B)

same

C)

higher

D)

None of the above

Correct Answer : lower

167 .

The amount of heat flow through a body by conduction is

A)

inversely proportional to the thickness of the body

B)

directly proportional to the surface area of the body

C)

directly proportional to the temperature difference on the two faces of the body

D)

All of the above

Correct Answer : All of the above

168 .

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

A)

negative

B)

zero

C)

positive

D)

None of the above

Correct Answer : zero

169 .

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

Correct Answer : 0.1 m

170 .

In a domestic vapour compression refrigerator, the refrigerant commonly used is

A)

COâ‚‚

B)

Ammonia

C)

R-12

D)

None of the above

Correct Answer : R-12

171 .

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

A)

minimum energy

B)

maximum energy

C)

Can Not Say

D)

None of the above

Correct Answer : maximum energy

172 .

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

A)

receiver and evaporator

B)

condenser and receiver

C)

compressor and condenser

D)

evaporator and compressor

Correct Answer : receiver and evaporator

173 .

Fouling factor is used

A)

in case of Newtonian fluids

B)

when a liquid exchanges heat with a gas

C)

in heat exchanger design as a safety factor

D)

None of the above

Correct Answer : in heat exchanger design as a safety factor

174 .

Bell-Coleman cycle is a

A)

reversed Otto cycle

B)

reversed Carnot cycle

C)

reversed Rankine cycle

D)

reversed Joule cycle

Correct Answer : reversed Joule cycle

175 .

The process, generally used in winter air-conditioning to warm and humidity the air, is called

A)

humidification.

B)

heating and humidification

C)

dehumidification

D)

cooling and dehumidification

Correct Answer : heating and humidification

176 .

The natural convection air cooled condensers are used in

A)

water coolers

B)

room air conditioners

C)

domestic refrigerators

D)

All of the above

Correct Answer : domestic refrigerators

177 .

Sulphur dioxide is extremely toxic and non-flammable.

A)

True

B)

False

C)

Can Not Say

D)

None of the above

Correct Answer : True

178 .

Which of the following statement is correct for ammonia as a refrigerant?

A)

It is toxic to mucous membranes.

B)

It reacts with copper and its alloys.

C)

it requires large displacement per TR compared to fluoro carbons.

D)

All of the above

Correct Answer : All of the above

179 .

The specific humidity during cooling and dehumidification

A)

increases

B)

decreases

C)

remains constant

D)

None of the above

Correct Answer : decreases

180 .

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 the above

Correct Answer : 3.5/C.O.P.

181 .

The process of heat transfer from one particle of the fluid to another by the actual movement of the fluid particles due to difference of density caused by temperature of the particle is known as

A)

radiation

B)

conduction

C)

free convection

D)

forced convection

Correct Answer : free convection

182 .

The thermostatic expansion valve is also called

A)

constant pressure valve

B)

constant temperature valve

C)

constant superheat valve

D)

None of the above

Correct Answer : constant superheat valve

183 .

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

A)

water coolers

B)

room air conditioners

C)

domestic refrigerators

D)

All of the above

Correct Answer : All of the above

184 .

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

A)

wet vapour region

B)

sub-cooled liquid region

C)

superheated vapour region

D)

None of the above

Correct Answer : sub-cooled liquid region

185 .

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

A)

copper

B)

steel

C)

brass

D)

aluminium

Correct Answer : copper

186 .

In aircraft, air refrigeration Cycle is used because of

A)

high heat transfer rate

B)

low weight per tonne of refrigeration

C)

higher coefficient of performance

D)

low temperature at high altitudes

Correct Answer : low weight per tonne of refrigeration

187 .

The wet bulb depression indicates __________ humidity of the air.

A)

specific

B)

absolute

C)

relative

D)

None of the above

Correct Answer : relative

188 .

The refrigerant widely used in domestic refrigerators is

A)

R-12

B)

ammonia

C)

carbon dioxide

D)

sulphur dioxide

Correct Answer : R-12

189 .

When absorptivity (α) = 1, reflectivity (ρ) = 0 and transmittivity (τ) = 0, then the body is said to be a

A)

grey body

B)

white body

C)

opaque body

D)

black body

Correct Answer : black body

190 .

In a vapour compression system, the condition of refrigerant before passing through the condenser is

A)

wet vapour

B)

saturated liquid

C)

dry saturated vapour

D)

superheated vapour

Correct Answer : superheated vapour

191 .

A composite slab has two layers of different materials with thermal conductivities k₁ and k₂. If each layer has the same thickness, then the equivalent thermal conductivity of the slab will be

A)

k₁ k₂

B)

k₁ + k₂

C)

k₁ + k₂ / k₁ k₂

D)

2k₁ k₂ / k₁ + k₂

Correct Answer : 2k₁ k₂ / k₁ + k₂

192 .

The critical temperature is the temperature

A)

below which a gas is always liquified

B)

above which a gas may explode

C)

above which a gas will never liquified

D)

below which a gas does not obey gas laws

Correct Answer : above which a gas will never liquified

193 .

In case of sensible cooling of air, the coil efficiency is given by

A)

B.P.F. - 1

B)

1 - B.P.F.

C)

1 + B.P.F.

D)

None of the above

Correct Answer : 1 - B.P.F.

194 .

For air conditioning the operation theatre in a hospital, the percentage of outside air in the air supplied is

A)

0

B)

20

C)

50

D)

100

Correct Answer : 100

195 .

The evaporator changes the low pressure liquid refrigerant from the expansion valve into

A)

low pressure vapour refrigerant

B)

high pressure liquid refrigerant

C)

low pressure liquid and vapour refrigerant

D)

None of the above

Correct Answer : low pressure vapour refrigerant

196 .

In a vapour compression refrigeration system, a throttle valve is used in place of an expander because

A)

it leads to significant cost reduction

B)

it considerably reduces mass of the system

C)

the positive work in isentropic expansion of liquid is very small

D)

it improves the C.O.P., as the condenser is small

Correct Answer : the positive work in isentropic expansion of liquid is very small

197 .

The unit of overall coefficient of heat transfer is

A)

W/m

B)

W/mK

C)

W/mÂ²

D)

W/mÂ²K

Correct Answer : W/mÂ²K

198 .

For large tonnage (more than 200 TR) air-conditioning applications, the compressor recommended is

A)

screw

B)

centrifugal

C)

rotating

D)

reciprocating

Correct Answer : centrifugal

199 .

Most thermostatic expansion valves are set for a superheat of

A)

5Â°C

B)

10Â°C

C)

15Â°C

D)

20Â°C

Correct Answer : 5Â°C

200 .

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

A)

Agree

B)

Disagree

C)

Can Not Say

D)

None of the above

Correct Answer : Agree

201 .

The radiation emitted by a black body is known as

A)

full radiation

B)

total radiation

C)

black radiation

D)

All of the above

Correct Answer : All of the above

202 .

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

A)

radiation

B)

conduction

C)

convection

D)

None of the above

Correct Answer : convection

203 .

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)

Both (A) and (B)

D)

Either (A) and (B)

Correct Answer : Both (A) and (B)

204 .

The super-heating in a refrigeration cycle

A)

increases C.O.P.

B)

decreases C.O.P.

C)

does not alter C.O.P.

D)

None of the above

Correct Answer : decreases C.O.P.

205 .

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

A)

superheated vapour

B)

wet vapour

C)

saturated liquid

D)

dry saturated vapour

Correct Answer : superheated vapour

206 .

In mechanical refrigeration system, the refrigerant has the maximum temperature

A)

in evaporator

B)

before expansion valve

C)

between condenser and evaporator

D)

between compressor and condenser

Correct Answer : between compressor and condenser

207 .

The leakage in a refrigeration system using freon is detected by

A)

sulphur sticks

B)

halide torch

C)

soap and water

D)

All of the above

Correct Answer : halide torch

208 .

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

A)

wet vapour

B)

dry saturated vapour

C)

saturated liquid

D)

superheated vapour

Correct Answer : saturated liquid

209 .

The capacity of a domestic refrigerator is in the range of

A)

5 to 7 TR

B)

3 to 5 TR

C)

1 to 3 TR

D)

0.1 to 0.3 TR

Correct Answer : 0.1 to 0.3 TR

210 .

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

C)

Can Not Say

D)

None of the above

Correct Answer : Yes

211 .

The process of heat transfer from one particle of the fluid to another by the actual movement of the fluid particles caused by some mechanical means, is known as

A)

radiation

B)

forced convection

C)

conduction

D)

free convection

Correct Answer : forced convection

212 .

The relative humidity __________ as air gets drier.

A)

increases

B)

decreases

C)

Can Not Say

D)

None of the above

Correct Answer : increases

213 .

When Î± is absorptivity, Ï is reflectivity and Ï„ is transmittivity, then for a diathermanous body,

A)

Î± = 0, Ï = 1 and Ï„ = 0

B)

Î± = 1, Ï = 0 and Ï„ = 0

C)

Î± + Ï = 1 and Ï„ = 0

D)

Î± = 0, Ï = 0 and Ï„ = 1

Correct Answer : Î± + Ï = 1 and Ï„ = 0

214 .

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

A)

Correct

B)

Incorrect

C)

Can Not Say

D)

None of the above

Correct Answer : Correct

215 .

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)

Newton's law of gases

B)

Kinetic theory of gases

C)

Avogadro's hypothesis

D)

Dalton's law of partial pressures

Correct Answer : Dalton's law of partial pressures

216 .

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

Correct Answer : saturated air

217 .

The expansion valve in a refrigerator controls the flow of refrigerant.

A)

Correct

B)

Incorrect

C)

Can Not Say

D)

None of the above

Correct Answer : Correct

218 .

The relative humidity lines on a psychrometric chart are

A)

vertical and uniformly spaced

B)

curved lines

C)

horizontal and uniformly spaced

D)

horizontal and non-uniformly spaced

Correct Answer : curved lines

219 .

The rato of energy transferred by convection to that by conduction is called

A)

Biot number

B)

Peclet number

C)

Stanton number

D)

Nusselt number

Correct Answer : Nusselt number

220 .

A vapour absorption refrigeration system

A)

cools below 0Â° C

B)

gives quiet operation

C)

gives noisy operation

D)

requires little power consumption

Correct Answer : gives quiet operation

221 .

The inclined and non-uniformly spaced straight lines on a psychrometric chart indicates wet bulb temperature.

A)

Agree

B)

Disagree

C)

Can Not Say

D)

None of the above

Correct Answer : Agree

222 .

A designer chooses the values of fluid flow rates and specific heats in such a manner that the heat capacities of the two fluids are equal. A hot fluid enters the counter flow heat exchanger at 100° C and leaves at 60° C. A cold fluid enters the heat exchanger at 40° C. The mean temperature difference between the two fluids is

A)

20°C

B)

40°C

C)

60°C

D)

66.7°C

Correct Answer : 20°C

223 .

A refrigerating system operating on reversed Brayton refrigeration cycle is used for maintaining 250 K. If the temperature at the end of constant pressure cooling is 300 K and rise in the temperature of air in the refrigerator is 50 K, then the net work of compression will be (assume air as working substance with c<sub>p</sub> = 1 kJ/kg)

A)

25 kJ/kg

B)

50 kJ/kg

C)

100 kJ/kg

D)

125 kJ/kg

Correct Answer : 50 kJ/kg

224 .

During adiabatic saturation process on unsaturated air __________ remains constant.

A)

relative humidity

B)

dry bulb temperature

C)

wet bulb temperature

D)

dew point temperature

Correct Answer : wet bulb temperature

225 .

The thickness of thermal and hydrodynamic boundary layer is equal if Prandtl number is

A)

equal to one

B)

less than one

C)

greater than one

D)

equal to Nusselt number

Correct Answer : equal to one

226 .

The coefficient of performance of Heat Pump is always __________ one.

A)

equal to

B)

less than

C)

greater than

D)

None of the above

Correct Answer : greater than

227 .

Degree of saturation or percentage humidity is

A)

the mass of water vapour present in 1 kg of dry air

B)

the mass of water vapour present in 1 m3 of dry air

C)

the ratio of actual mass of water vapour in a given volume of moist air to the mass of water vapour in the same volume of saturated air at the same temperature and pressure

D)

the ratio of the actual mass of water vapour in a unit mass of dry air to the mass of water vapour in the same mass of dry air when it is saturated at the same temperature and pressure.

Correct Answer : the ratio of the actual mass of water vapour in a unit mass of dry air to the mass of water vapour in the same mass of dry air when it is saturated at the same temperature and pressure.

228 .

A perfect black body is one which

A)

is black in colour

B)

absorbs heat radiations of all wave lengths falling on it

C)

transmits the heat radiations

D)

reflects all the heat radiations

Correct Answer : absorbs heat radiations of all wave lengths falling on it

229 .

During a refrigeration cycle, heat is rejected by the refrigerant in a

A)

condenser

B)

evaporator

C)

compressor

D)

expansion valve

Correct Answer : condenser

230 .

During sensible cooling of air __________ decreases.

A)

relative humidity

B)

specific humidity

C)

wet bulb temperature

D)

dry bulb temperature

Correct Answer : dry bulb temperature

231 .

The subcooling in a refrigeration cycle

A)

decreases C.O.P.

B)

does not alter C.O.P.

C)

increases C.O.P.

D)

None of the above

Correct Answer : increases C.O.P.

232 .

A refrigeration system

A)

rejects energy to a low temperature body

B)

removes heat from a high temperature body and delivers it to a low temperature body

C)

removes heat from a low temperature body and delivers it to a high temperature body

D)

None of the above

Correct Answer : removes heat from a low temperature body and delivers it to a high temperature body

233 .

In order to cool and dehumidify a stream of moist air, it must be passed over the coil at a temperature

A)

of adiabatic saturation of incoming stream

B)

which is lower than the dew point temperature of the incoming stream

C)

which lies between the dry bulb and wet bulb temperatures of the incoming stream

D)

which lies between the wet bulb and dew point temperatures of the incoming stream

Correct Answer : which is lower than the dew point temperature of the incoming stream

234 .

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

A)

low

B)

high

C)

Can Not Say

D)

None of the above

Correct Answer : high

235 .

Which of the following refrigerant has the lowest boiling point?

A)

Carbon dioxide

B)

R-12

C)

Ammonia

D)

Sulphur dioxide

Correct Answer : Carbon dioxide

236 .

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)

condenser

B)

evaporator

C)

expansion valve

D)

compressor

Correct Answer : compressor

237 .

The wet bulb temperature at 100% relative humidity is __________ dew point temperature.

A)

same as

B)

lower than

C)

higher than

D)

None of the above

Correct Answer : same as

238 .

Which of the following statement is correct?

A)

A perfect body is one which is black in colour.

B)

At thermal equilibrium, the emissivity and absorptivity are same.

C)

A grey body is one which absorbs all radiations incident on it.

D)

The energy absorbed by a body to the total energy falling on it, is called emissivity.

Correct Answer : At thermal equilibrium, the emissivity and absorptivity are same.

239 .

The use of heat exchangers is made in

A)

radiators in automobile

B)

condensers and boilers in steam plants

C)

condensers and evaporators in refrigeration and air conditioning units

D)

All of the above

Correct Answer : All of the above

240 .

In a heat exchanger with one fluid evaporating or condensing, the surface area required is least in

A)

cross flow

B)

parallel flow

C)

counter flow

D)

All of the above

Correct Answer : All of the above

241 .

The sensible heat gain is due to the __________ difference between the fresh air and the air in space.

A)

humidity

B)

temperature

C)

Can Not Say

D)

None of the above

Correct Answer : temperature

242 .

The sulphur sticks, in case of leakage of ammonia refrigerant, gives white smoke.

A)

True

B)

False

C)

Can Not Say

D)

None of the above

Correct Answer : True

243 .

The coefficient of performance of electrolux refrigerator is the ratio of

A)

heat supplied by the gas burner to the heat absorbed by the evaporator

B)

heat supplied by the gas burner minus the heat absorbed by the evaporator to the heat supplied by the gas burner

C)

heat absorbed by the evaporator to the heat supplied by the gas burner

D)

heat absorbed by the evaporator minus the heat supplied by the gas burner to the heat absorbed by the evaporator

Correct Answer : heat absorbed by the evaporator to the heat supplied by the gas burner

244 .

During cooling and dehumidification, dry bulb temperature

A)

increases

B)

remains constant

C)

decreases

D)

None of the above

Correct Answer : decreases

245 .

During sensible heating of air __________ decreases.

A)

specific humidity

B)

relative humidity

C)

wet bulb temperature

D)

dry bulb temperature

Correct Answer : relative humidity

246 .

The overall coefficient of heat transfer is used in problems of

A)

radiation

B)

convection

C)

conduction

D)

conduction and convection

Correct Answer : conduction and convection

247 .

The ratio of actual mass of water vapour in a given volume of moist air to the mass of water vapour in the same volume of saturated air at the same temperature and pressure, is called

A)

relative humidity

B)

humidity ratio

C)

absolute humidity

D)

degree of saturation

Correct Answer : relative humidity

248 .

The space between the two walls of a thermos flask is evacuated because vacuum is a __________ conductor of heat.

A)

good

B)

bad

C)

Can Not Say

D)

None of the above

Correct Answer : bad

249 .

The transfer of heat by molecular collision is smallest in

A)

solids

B)

liquids

C)

gases

D)

None of the above

Correct Answer : gases

250 .

During dehumidification process, the relative humidity

A)

increases

B)

remains constant

C)

decreases

D)

None of the above

Correct Answer : decreases

251 .

Thermal conductivity of a material may be defined as the

A)

quantity of heat flowing in one second through one cm of material when opposite faces are maintained at a temperature difference of 1Â° C

B)

quantity of heat flowing in one second through a slab of the material of area 1 cm2 and thickness 1 cm when its faces differ in temperature by 1Â° C

C)

heat conducted in unit time across unit area through unit thickness when a temperature difference of unity is maintained between opposite faces

D)

All of the above

Correct Answer : All of the above

252 .

Air refrigeration cycle is used in

A)

gas liquefaction

B)

air-conditioning

C)

domestic refrigerators

D)

commercial refrigerators

Correct Answer : gas liquefaction

253 .

The wet bulb depression is zero when relative humidity is

A)

1.0

B)

0.75

C)

0.5

D)

zero

Correct Answer : 1.0

254 .

Reynolds number is the ratio of

A)

kinematic viscosity to thermal diffusivity

B)

inertia force to viscous force

C)

energy transferred by convection to that by conduction

D)

None of the above

Correct Answer : inertia force to viscous force

255 .

The ratio of emissive power of a body to the emissive power of a perfectly black body is called emissivity.

A)

Agree

B)

Disagree

C)

Can Not Say

D)

None of the above

Correct Answer : Agree

256 .

In a saturated air-water vapour mixture, the

A)

dry bulb temperature is higher than wet bulb temperature

B)

dew point temperature is lower than wet bulb temperature

C)

dry bulb, wet bulb and dew point temperature are same

D)

dry bulb temperature is higher than dew point temperature

Correct Answer : dry bulb, wet bulb and dew point temperature are same

257 .

The capillary tube is not used in large capacity refrigeration systems because

A)

cost is too high

B)

it is made of copper

C)

required pressure drop can not be achieved

D)

capacity control is not possible

Correct Answer : capacity control is not possible

258 .

Dew point temperature corresponds to the saturation temperature of vapour at its partial pressure.

A)

True

B)

False

C)

Can Not Say

D)

None of the above

Correct Answer : True

259 .

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

A)

lower

B)

higher

C)

same

D)

None of the above

Correct Answer : higher

260 .

In air-conditioning of aeroplanes, using air as a refrigerant, the cycle used is

A)

reversed Otto cycle

B)

reversed Joule cycle

C)

reversed Carnot cycle

D)

reversed Brayton cycle

Correct Answer : reversed Brayton cycle

261 .

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. This statement is known as

A)

Wien's law

B)

Planck's law

C)

Kirchhoff's law

D)

Stefan's law

Correct Answer : Kirchhoff's law

262 .

An ordinary passenger aircraft requires a cooling system of capacity.

A)

2 TR

B)

4 TR

C)

8 TR

D)

10 TR

Correct Answer : 8 TR

263 .

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

A)

one dimensional cases only

B)

two dimensional cases only

C)

irregular surfaces

D)

non-uniform temperature surfaces

Correct Answer : one dimensional cases only

264 .

Moisture should be removed from refrigerants to avoid

A)

corrosion of steel plates

B)

restriction to refrigerant flow

C)

freezing at the expansion valve

D)

All of the above

Correct Answer : All of the above

265 .

During humidification process, dry bulb temperature

A)

decreases

B)

remains constant

C)

increases

D)

None of the above

Correct Answer : remains constant

266 .

For unsaturated air, the dew point temperature is __________ wet bulb temperature.

A)

equal to

B)

less than

C)

more than

D)

None of the above

Correct Answer : less than

267 .

The heat is transferred by conduction, convection and radiation in

A)

melting of ice

B)

condensation of steam in condenser

C)

boiler furnaces

D)

None of the above

Correct Answer : boiler furnaces

268 .

The ratio of the actual mass of water vapour in a unit mass of dry air to the mass of water vapour in the same mass of dry air when it is saturated at the same temperature and pressure, is called

A)

degree of saturation

B)

humidity ratio

C)

relative humidity

D)

absolute humidity

Correct Answer : degree of saturation

269 .

A thermostatic expansion valve in a refrigeration system

A)

is suitable only for constant load systems

B)

maintains different temperatures in evaporator in proportion to load

C)

Both (A) and (B)

D)

ensures the evaporator completely filled with refrigerant of the load

Correct Answer : ensures the evaporator completely filled with refrigerant of the load

270 .

The critical radius is the insulation radius at which the resistance to heat flow is

A)

minimum

B)

zero

C)

maximum

D)

None of the above

Correct Answer : minimum

271 .

The temperature of ammonia after compression in a vapour compression system is

A)

50 to 70Â° C

B)

70 to 110Â° C

C)

20 to 50Â° C

D)

None of the above

Correct Answer : 70 to 110Â° C

272 .

A water cooled condenser operates at a __________ condensing temperature than an air-cooled condenser.

A)

higher

B)

lower

C)

Can Not Say

D)

None of the above

Correct Answer : lower

273 .

In actual air-conditioning applications for R-12 and R-22, and operating at a condenser temperature of 40° C and an evaporator temperature of 5° C, the heat rejection factor is about

A)

5.12

B)

2.15

C)

1.25

D)

1

Correct Answer : 1.25

274 .

Radiation is the process of heat transfer in which heat flows from a __________ , in a straight line, without affecting the intervening medium.

A)

smaller body to larger body

B)

cold body to hot body

C)

hot body to cold body

D)

larger body to smaller body

Correct Answer : hot body to cold body

275 .

The undesireable property of a refrigerant is

A)

non-toxic

B)

non-explosive

C)

non-flammable

D)

high boiling point

Correct Answer : high boiling point

276 .

The conditioned air supplied to the room must have the capacity to take up

A)

room sensible heat load only

B)

room latent heat load only

C)

both room sensible heat and latent heat loads

D)

None of the above

Correct Answer : both room sensible heat and latent heat loads

277 .

Which of the following refrigerant has the lowest freezing point?

A)

R-22

B)

R-12

C)

R-11

D)

Ammonia

Correct Answer : R-22

278 .

For a white body, absorptivity (α ) = 0, reflectivity (ρ) = 1 and transmittivity (τ) = 0.

A)

Correct

B)

Incorrect

C)

Can Not Say

D)

None of the above

Correct Answer : Correct

279 .

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

A)

reduce

B)

increase

C)

equalise

D)

None of the above

Correct Answer : increase

280 .

The wet bulb temperature during sensible cooling of air

A)

increases

B)

remains constant

C)

decreases

D)

None of the above

Correct Answer : decreases

281 .

The thermostatic expansion valve operates on the changes in the

A)

pressure in the evaporator

B)

temperature of the evaporator

C)

Both (A) and (B)

D)

degree of superheat at exit from the evaporator

Correct Answer : degree of superheat at exit from the evaporator

282 .

The unit of thermal diffusivity is

A)

m/h

B)

m/hK

C)

mÂ²/h

D)

mÂ²/hK

Correct Answer : mÂ²/h

283 .

The refrigerant supplied to a compressor must be

A)

superheated vapour refrigerant

B)

dry saturated liquid refrigerant

C)

a mixture of liquid and vapour refrigerant

D)

None of the above

Correct Answer : superheated vapour refrigerant

284 .

In a vapour compression system, the condition of refrigerant before entering the expansion or throttle valve is

A)

dry vapour

B)

wet vapour

C)

very wet vapour

D)

high pressure saturated liquid

Correct Answer : high pressure saturated liquid

285 .

The freezing point of R-12 is

A)

-107.7Â°C

B)

-135.8Â°C

C)

-95.2Â°C

D)

-86.6Â°C

Correct Answer : -135.8Â°C

286 .

The specific humidity during humidification process

A)

increases

B)

decreases

C)

remains constant

D)

None of the above

Correct Answer : remains constant

287 .

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

Correct Answer : two cooling turbines and one heat exchanger

288 .

The heat of sun reaches to us according to

A)

radiation

B)

convection

C)

conduction

D)

None of the above

Correct Answer : radiation

289 .

The product of Reynolds number and Prandtl number is known as

A)

Biot number

B)

Stanton number

C)

Grashoff number

D)

Peclet number

Correct Answer : Peclet number

290 .

Carbon dioxide is

A)

colourless

B)

odourless

C)

non-flammable

D)

All of the above

Correct Answer : All of the above

291 .

During dehumidification process, __________ remains constant.

A)

specific humidity

B)

dry bulb temperature

C)

relative humidity

D)

wet bulb temperature

Correct Answer : dry bulb temperature

292 .

Emissivity of a body will be equal to its absorptivity at all temperatures.

A)

Yes

B)

No

C)

Can Not Say

D)

None of the above

Correct Answer : Yes

293 .

The value of the wave length for maximum emissive power is given by

A)

Wein's law

B)

Stefan's law

C)

Planck's law

D)

Kirchhoff's law

Correct Answer : Wein's law