Q1. ________ is a very common refrigerant used extensively in high capacity refrigeration plant.

1. Nitrogen
2. Ammonia
3. CO2
4. Oxygen

ANSWER: B. Ammonia

• Explanation – Ammonia is a common refrigerant that is often utilized in large refrigeration plants. It meets the majority of the criteria given above. It is, nevertheless, poisonous, irritating, and combustible. Halogenated hydrocarbons are widely utilized in domestic freezers and air conditioning, among other things.

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Q2. The basic principle of mechanical refrigeration cycle is based on cyclic thermodynamic process known as

1. Rankine-cycle
2. Vapour compression cycle
3. None of the above
4. Both A and B

ANSWER: D. Both A and B

• Explanation – The mechanical refrigeration cycle is based on the Rankine-cycle or vapour compression cycle, which is a cyclic thermodynamic process. There are four parts to the cycle. The phase of the refrigerant changes from liquid to gas and back to liquid as it passes through these components. Compression, condensation, expansion, and evaporation are the components.

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Q3. Psychrometry is the study of thermodynamic properties of _______.

1. Moist air
2. Ice crystals
3. Water vapour
4. All of the above

ANSWER – A. Moist air

• Explanation: The heating medium for food processing operations, particularly drying operations, is atmospheric air. It is unavoidable to investigate the properties of atmospheric air in order to develop and control such operations. Another major area in food processing where the thermodynamic properties of moist air must be carefully assessed is air conditioning. The study of the thermodynamic properties of an air-water vapour mixture is known as psychrometry (moist air).

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Q4. The molecular weight of water is ______.

1. 18.01534
2. 12.165
3. 8.873
4. 4.657

ANSWER: A. 18.01534

• Explanation: All psychrometric qualities are based on the premise that dry air acts like an ideal gas. Because these gases do not change states at normal temperatures and pressures, they can be regarded a single gas known as ‘dry air.’ Dry air has an apparent molecular weight of 28.9645 and a gas constant of 287.055 m3Pa/kgK. Water has a molecular weight of 18.01534.

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Q5. ______ is the heat required to raise the temperature to one unit of a unit mass of air.

1. Specific heat
2. Enthalpy
3. Specific volume
4. Dry bulb temperature

ANSWER: A. Specific heat

• Explanation – The heat required to increase the temperature to one unit of a unit mass of air is known as specific heat. cpa=1.005 kJ/kgK is the average specific heat of dry air at one atmospheric temperature. Water vapour has a specific heat of cpw=1.88 kJ/kgK.

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