Refrigeration And Air Conditioning — Part 2 MCQs with Explanations

In the vapor compression refrigeration cycle, the refrigerant undergoes phase changes and pressure variations as it moves through different components of the system. Explanation for each option: After passing through the condenser : The refrigerant is in a high-pressure saturated liquid state after it has released heat and condensed in the condenser. Before passing through the condenser : This is not the correct condition. Before the condenser, the refrigerant is typically in a high-pressure, high-temperature, and superheated vapor state. After passing through the expansion or throttle valve : After passing through the expansion valve, the refrigerant undergoes a pressure drop and enters the evaporator as a low-pressure, low-temperature mixture of liquid and vapor. Before entering the expansion valve : This is not the correct condition. Before the expansion valve, the refrigerant is typically in a high-pressure, high-temperature, and superheated vapor state. Therefore, in the context of the question, the condition of the refrigerant as a high-pressure saturated liquid occurs after passing through the condenser

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

In vapour compression cycle the condition off refrigerant is dry saturated vapour Before entering the compressor

R-12 (Dichlorodifluoromethane) has been traditionally used in small tonnage commercial machines and hermetically sealed refrigeration units such as domestic refrigerators and small air-conditioning systems. It is preferred because it is non-toxic, non-flammable, chemically stable , and has good thermodynamic properties , making it highly suitable for sealed systems where maintenance is minimal. Other options like Ammonia are toxic, Carbon dioxide operates at very high pressures, and Sulphur dioxide is corrosive and toxic, which makes them unsuitable for small hermetically sealed units. Although R-12 is now phased out due to its ozone depletion potential , it remains the correct theoretical answer for traditional refrigeration systems in examination contexts.

The refrigeration effect in a dry evaporator compared to flooded evaporator in a similar plant is Less

Highest pressure encountered in a refrigeration system should be Much below critical pressure

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

The Bell Coleman Cycle also called as the Joule or "reverse" Brayton cycle. it is a refrigeration cycle where the working fluid is a gas that is compressed and expanded, but does not change phase.

The heat rejection factor (HRF) is given by $$1 + \frac{1}{{{\text{C}}{\text{.O}}{\text{.P}}{\text{.}}}}$$

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

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 m 2 /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.

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

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

The coefficient of performance is the ratio of the refrigerant effect to the - Heat of compression - Work done by compressor - Enthalpy increase in compressor

In refrigerator, liquid receiver is required between condenser and flow controlling device, if quantity of refrigerant for system is More than or equal to 3.65 kg

Pressure of water vapour is given by, $$ln\left( {\frac{{{{\text{P}}_1}}}{{{{\text{P}}_2}}}} \right) = \left( {\frac{{\Delta {\text{Hvap}}}}{{\text{R}}}} \right)\left( {\frac{1}{{{{\text{T}}_2}}} - \frac{1}{{{{\text{T}}_1}}}} \right)$$

In vapour compression cycle using NH 3 as refrigerant, initial charge is filled at high pressure side close to receiver.

If a heat pump cycle operates between the condenser temperature of +27°C and evaporator temperature of -23°C, then the Carnot COP will be 6

Vertical lines on pressure-enthalpy chart show constant Total heat lines

A vapour absorption refrigerator uses Aqua-ammonia as a refrigerant. In the vapor absorption system the refrigerant used is ammonia, water or lithium bromide. The refrigerant gets condensed in the condenser and it gets evaporated in the evaporator. The refrigerant produces cooling effect in the evaporator and releases the heat to the atmosphere via the condenser.

Advantages of ammonia as a refrigerant: - It is toxic to mucous membranes. - It requires large displacement per TR compared to fluoro carbons. - It reacts with copper and its alloys.

In vapour compression refrigeration system, refrigerant occurs as liquid between Expansion valve and evaporator

Dalton's law also called Dalton's law of partial pressures, it states that in a mixture of non-reacting gases, the total pressure exerted is equal to the sum of the partial pressures of the individual gases.

one ton of refrigeration is equal to 210 kJ/ min

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

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

Air refrigeration operates on Brayton cycle

The C.O.P. of an absorption type refrigerator is given by $$\frac{{{{\text{T}}_3}\left( {{{\text{T}}_1} - {{\text{T}}_2}} \right)}}{{{{\text{T}}_1}\left( {{{\text{T}}_2} - {{\text{T}}_3}} \right)}}$$ (Where T 1 = Temperature at which the working substance receives heat, T 2 = Temperature of cooling water and T 3 = Evaporator temperature)

The critical temperature of a substance is the temperature at and above which vapor of the substance cannot be liquefied, no matter how much pressure is applied

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

Absolute humidity is the measure of water vapor (moisture) in the air, regardless of temperature. It is expressed as grams of moisture per cubic meter of air (g/m 3 ).

An Electrolux refrigerator is called a Three fluids absorption system.