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4

Formation of frost on evaporator in refrigerator

A. Results in loss of heat due to poor heat transfer

B. Increases heat transfer rate

C. Is immaterial

D. Can be avoided by proper design

Correct Answer :

A. Results in loss of heat due to poor heat transfer


Related Questions

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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. Positive

B. Negative

C. Zero

D. None of these

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4

A vapour absorption refrigerator uses __________ as a refrigerant.

A. Water

B. Ammonia

C. Freon

D. Aqua-ammonia

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4

In vapour compression cycle the condition off refrigerant is dry saturated vapour

A. After passing through the condenser

B. Before passing through the condenser

C. After passing through the expansion or throttle valve

D. Before entering the compressor

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4

During sensible cooling of air ________ decreases.

A. Wet bulb temperature

B. Relative humidity

C. Dry bulb temperature

D. Specific humidity

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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

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4

Which of the following refrigerant has the lowest boiling point?

A. Ammonia

B. Carbon dioxide

C. Sulphur dioxide

D. R-12

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4

One ton refrigeration corresponds to

A. 50 kcal/ min

B. 50 kcal/ hr

C. 80 kcal/ min

D. 80 kcal/ hr

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4

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

A. Sub-cooling or under-cooling

B. Super-cooling

C. Normal cooling

D. None of these

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4

Superheating in a refrigeration cycle

A. Increases C.O.P

B. Decreases C.O.P

C. C.O.P remains unaltered

D. Other factors decide C.O.P

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4

The curved lines on a psychrometric chart indicates

A. Dry bulb temperature

B. Wet bulb temperature

C. Dew point temperature

D. Relative humidity

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4

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. 1 + B.P.F.

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4

The specific humidity during humidification process

A. Remains constant

B. Increases

C. Decreases

D. None of these

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4

During heating and humidification, the final relative humidity of air

A. Can be lower or higher than that of the entering air

B. Is lower than that of the entering air

C. Is higher than that of the entering air

D. None of the above

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4

Which of the following statement is wrong?

A. The value of C.O.P. is always greater than one.

B. In a vapour compression system, the condition of refrigerant before entering the compressor is dry saturated vapour.

C. The space between the saturated liquid line and saturated vapour line, in a pressure enthalpy chart, is wet vapour region.

D. None of the above

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4

Nusselt number (NN) is given by

A. NN = hl/k

B. NN = μ cp/k

C. NN = ρ V l /μ

D. NN = V²/t.cp

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4

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

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4

The boiling point of ammonia is

A. 100°C

B. 50°C

C. 33.3°C

D. 0°C

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4

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

A. Condenser

B. Evaporator

C. Absorber

D. None of these

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4

The evolution of heat of solution takes place in ammonia absorption plant when

A. Ammonia vapour goes into solution

B. Ammonia vapour is driven out of solution

C. Lithium bromide mixes with ammonia

D. Weak solution mixes with strong solution

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4

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 + 2

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

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4

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. Humidity ratio

B. Relative humidity

C. Absolute humidity

D. Degree of saturation

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4

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

A. Same

B. Lower

C. Higher

D. None of these

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4

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

A. Reversed Carnot cycle

B. Reversed Joule cycle

C. Reversed Brayton cycle

D. Reversed Otto cycle

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4

Mass flow ratio of NH₃ in comparison to Freon12 for same refrigeration load and same temperature limits is of the order of

A. 1 : 1

B. 1 : 9

C. 9 : 1

D. 1 : 3

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4

The specific humidity during cooling and dehumidification

A. Remains constant

B. Increases

C. Decreases

D. None of these

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4

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

A. Automatic expansion valve

B. High side float valve

C. Thermostatic expansion valve

D. Low side float valve

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4

The lower horizontal line of the refrigeration cycle plotted on pressure-enthalpy diagram represents

A. Condensation of the refrigerant vapour

B. Evaporation of the refrigerant liquid

C. Compression of the refrigerant vapour

D. Metering of the refrigerant liquid

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4

In a lithium bromide absorption refrigeration system

A. Lithium bromide is used as a refrigerant and water as an absorbent

B. Water is used as a refrigerant and lithium bromide as an absorbent

C. Ammonia is used as a refrigerant and lithium bromide as an absorbent

D. None of the above

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4

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

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4

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

A. Reciprocating

B. Rotating

C. Centrifugal

D. Screw