Refrigeration And Air Conditioning MCQ Questions & Answers | Mechanical Engineering

The lowest thermal diffusivity is of Rubber

The central air conditioning system has Higher overall efficiency as compared to individual systems.

For air conditioning the operation theater in a hospital, the percentage of outside air in the air supplied is 100

The vapor compression refrigeration cycle employed by a typical refrigerator is a Reversed Rankine cycle. The Rankine cycle is commonly used in thermodynamic systems, especially in power plants, to convert heat energy into mechanical work. However, in a refrigeration system, the Rankine cycle is reversed to create a cooling effect.

The basic components of a vapor compression refrigeration system include a compressor, a condenser, an expansion valve, and an evaporator. Here's how the Reversed Rankine cycle works in a refrigerator:

1. Compression: The low-pressure, low-temperature vapor from the evaporator is compressed by the compressor, increasing its pressure and temperature.
2. Condensation: The high-pressure, high-temperature vapor is then condensed to a liquid in the condenser, releasing heat to the surroundings.
3. Expansion: The high-pressure liquid refrigerant passes through an expansion valve, where its pressure and temperature drop significantly, causing it to partially vaporize.
4. Evaporation: The low-pressure, low-temperature vapor-liquid mixture enters the evaporator, where it absorbs heat from the refrigerated space, cooling it down.

Option A: The Rankine cycle is a thermodynamic cycle used in power plants, not refrigeration systems.
Option B: The Carnot cycle is a theoretical thermodynamic cycle that represents the maximum possible efficiency of a heat engine or refrigerator, but it is not typically used in practical refrigeration systems.
Option D: The Reversed Carnot cycle is a conceptually similar cycle to the Reversed Rankine cycle, but the Rankine cycle is more commonly associated with vapor compression refrigeration.

Therefore, the correct answer is Option C: Reversed Rankine, as it represents the cycle employed by a vapor compression refrigerator to provide cooling.

The atmospheric air at dry bulb temperature of 15°C enters a heating coil maintained at 40°C. The air leaves the heating coil at 25°C. The bypass factor of the heating coil is 0.6

During heating and humidification, the final relative humidity of air Can be lower or higher than that of the entering air

The thermostatic expansion valve is used in Dry type of evaporators.

Sensible heat factor (s.h.f.) is the ratio of sensible heat to the total heat.
So,
$$\eqalign{ & {\text{s}}{\text{.h}}{\text{.f}}{\text{.}} = \frac{{30}}{{30 + 20}} \cr & = \frac{{30}}{{50}} \cr & = 0.6 \cr} $$

A pressure gauge on the discharge side of a refrigerant compressor reads too high. The reasons will be
- Lack of cooling water
- Water temperature being high
- Dirty condenser surface

The change in evaporator temperature in a refrigeration cycle, as compared to change in condenser temperature, influences the value of C.O.P. more