Refrigeration And Air Conditioning MCQ Questions & Answers | Mechanical Engineering

The optimum effective temperature for human comfort is Lower in winter than in summer

In the domestic refrigerators the evaporators are commonly known as the freezers since the ice is made in these compartments. In case of the window and split air conditioners and other air conditioning systems where the evaporator is directly used for cooling the room air, it is called as the cooling coil.

The refrigerant vaporizes from the heat it absorbs heat in the evaporator. Flow control device (expansion valve): This controls the flow of the liquid refrigerant into the evaporator. Control devices usually are thermostatic, meaning that they are responsive to the temperature of the refrigerant.

Option A: Carnot cycle
The Carnot cycle is an ideal thermodynamic cycle that gives the maximum possible efficiency. It consists of two isothermal and two adiabatic processes. It is used only as a standard of comparison and cannot be practically implemented because isothermal compression and expansion are very difficult to achieve.

Option B: Reversed Rankine cycle
The vapour compression refrigeration system follows the processes of compression, condensation, expansion (throttling), and evaporation. These are the exact processes of the Reversed Rankine cycle. It is a practical and achievable cycle, which is why almost all refrigerators and air conditioners work on this principle.

Option C: Reversed Carnot cycle
The Reversed Carnot cycle is the theoretical model of refrigeration with the highest possible COP (Coefficient of Performance). However, it cannot be applied in real systems because achieving isothermal heat addition and rejection along with isentropic compression/expansion is practically impossible. So, it serves as an "ideal reference" but not the real working cycle.

Conclusion:
While the Reversed Carnot cycle is the ideal and most efficient refrigeration cycle, it is not feasible for practical use. The Vapour Compression Refrigeration system actually works on the Reversed Rankine cycle, which is why the correct answer is Option B: Reversed Rankine cycle.

Refrigerant with a lower latent heat of vaporization will absorb less energy during evaporation than those with higher hfg.
The temperature for a given pressure at which the gaseous refrigerant begins to condense into a liquid.

A refrigeration cycle operates between condenser temperature of +27°C and evaporator temperature of -23°C. The Carnot coefficient of performance of cycle will be 5.

The bypass factor (B.P.F.) in case of sensible heating of air is $$\frac{{{\text{t}}{{\text{d}}_3} - {\text{t}}{{\text{d}}_2}}}{{{\text{t}}{{\text{d}}_3} - {\text{t}}{{\text{d}}_1}}}$$
Where,
td₁ = Dry bulb temperature of air entering the heating coil,
td₂ = Dry bulb temperature of air leaving the heating coil and
td₃ = Dry bulb temperature of heating coil

The general rule for rating refrigeration systems (excepting for CO₂ system) is to approximate following h.p. per ton of refrigeration 1 to 2 h.p. per ton of refrigeration.

The freezing point of R-12 is -157.7°C

The coefficient of performance (C.O.P.) of a refrigerator working as a heat pump is given by (C.O.P.)_P = (C.O.P.)_R + 1