Refrigeration And Air Conditioning MCQ Questions & Answers | Mechanical Engineering

In a refrigerating machine, the heat rejected is less than the heat absorbed. This is due to the basic principle of refrigeration cycles, where heat is absorbed from the refrigerated space (or substance) at a low temperature and rejected to a higher temperature environment.

During the refrigeration cycle, the refrigerant absorbs heat from the evaporator, causing it to evaporate and thus cooling the refrigerated space. This absorbed heat is typically less than the heat rejected by the refrigerant in the condenser, as the heat rejected includes both the heat absorbed from the refrigerated space and the additional heat input required to overcome irreversibilities and losses in the system.

Therefore, the heat rejected is less than the heat absorbed in a refrigerating machine, making Option B: Less than the correct choice.

During sensible heating of air Relative humidity decreases.

During the cooling and humidification process the dry bulb of the air reduces, its wet bulb and the dew point temperature increases, while its moisture content and thus the relative humidity also increases.

The boiling point of Sulphur dioxide is 10.5°C.

In an ammonia absorption refrigeration system, the cycle includes four major processes: evaporation, absorption, generation, and condensation.

The absorber is the part where the system gives up heat to the surroundings.

In the absorber, ammonia vapour coming from the evaporator is absorbed into a weak ammonia solution (water + less ammonia), forming a strong solution.

This absorption is exothermic — it releases heat. That heat must be rejected to the surroundings, often via cooling water.

So, the correct description of where heat is released is: from ammonia vapours to the weak solution — which is exactly what Option D says.

Let’s now address the confusion:

Option B: "Weak solution to strong solution" — This describes the chemical result of the absorption, not the direction of heat flow. The solution becomes strong by absorbing ammonia, but this does not describe the process of heat transfer. It’s chemically correct but thermodynamically incomplete.

Option A: "Strong solution to weak solution" — This is incorrect. There is no heat given up by a strong solution to a weak one in the process.

Option C: "Strong solution to ammonia vapour" — This describes part of the generation process, which requires heat input, not heat rejection.

Therefore, the only option that directly and clearly identifies where the system gives up heat is:

Option D: Ammonia vapours to weak solution.

1 tonne of refrigeration is the rate of heat removal required to freeze a metric ton (1000 kg) of water at 0°C in 24 hours. Based on the heat of fusion being 333.55 kJ/kg, 1 tonne of refrigeration = 13,898 kJ/h = 3.861 kW

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 Cooled and humidified

The unit of thermal diffusivity is m²/h.

Ammonia is Highly toxic and inflammable
Ammonia is also used as a refrigerant gas, for purification of water supplies, and in the manufacture of plastics, explosives, textiles, pesticides, dyes and other chemicals.