Refrigeration and Air Conditioning Interview Questions and Answers:

1. What is practical unit of refrigeration ? Define it.

Ans. Tonne of refrigeration (TR) is the practical unit of refrig­eration and is defined as the amount of refrigeration effect produced by the uniform melting of one tonne (1,000 kg) of ice from and at 0°C in 24 hours.

2. What are the applications of vapour compression refrigera­tion cycle ?

Ans. The vapour compression refrigeration cycle is used in most of the modern refrigeration systems in large industrial plants requiring rapid removal of large amount of heat and in most of the domestic refrigerators.

3. On what principle does thermoelectric refrigeration system operate ?

Ans. Thermoelectric refrigeration system operates on the prin­ciple of ‘Peltier effect’.

4. What are the desirable properties of refrigerants ?

Ans. For safe, economical and thermodynamically efficient production of cold, refrigerant should possess as many as practicable of the following desirable properties.

1. Low boiling point.
2. High critical temperature.
3. High latent heat of vaporization.
4. Low specific volume of vapour.
5. Low specific heat of liquid.
6. Low cost.
7. Easy to liquify at moderate pressure and temperature.
8. Easy of locating leaks by odour or suitable indicator.
9. It should be noncorrosive.
10. It should be noninflammable.
11. It should be non-toxic.
12. It should be free from objectionable odour.

5. Why is ammonia the only common refrigerant used in the absorption system ?

Ans. Because ammonia is cheap, readily available and has the highest efficiency.

6. Why thermostat is used in a domestic refrigerator ?

Ans. Thermostat switch is provided in a domestic refrigerator to control the temperature inside a refrigerator.

7. With the aid of a sketch of a thermostat explain how the temperature inside a refrigerator is adjusted.

Ans. Thermostat is a thermal switch that is provided to control the temperature inside the refrigerator. Temperature inside the refrigerator can be adjusted by means of temperature control screw. Greater the distance between contacts, greater will be the temperature inside the refrigerator and vice versa.

8. Why it is not advisable to put very hot things into the refrig­erator ?

Ans. Main precaution to be taken is that very hot things should not be put in refrigerator, if it is done it will quickly evapo­rate the refrigerant in evaporator coils producing a large vapour pressure resulting in increase in the duty of the com­pressor and as such motor has to work for longer duration in order to bring down the temperature in the freezer compart­ment. It may damage the motor, which is short-time rated. Also moisture released from hot things will freeze around the freezer compartment which has to be defrosted.

9. Why is an automatic door closing mechanism provided in a modern refrigerator ?

Ans. The door is provided with automatic closing mechanism-door hinges are provided in such a way that door flap when left in open position automatically comes to closing position due to gravity and as it approaches closing position it is attracted by the magnetic strip fitted behind the sealing rubber ring and thus the door is closed with snap action. All this is done to prevent leakage of atmospheric heat inside the refrigerator.

10. What will happen if automatic starter relay stops to oper­ate in refrigerator ?

Ans. Capacitor-start single phase induction motor is used in open type refrigerators and split-phase single phase induction motor is used in sealed unit refrigerator. Electromagnetic relay is provided to connect auxiliary winding on the start and disconnect it when the motor picks up the speed.

If the automatic starter relay keeps the auxiliary winding open after the motor has been operating, little harm should occur since the motor is provided with overcurrent protection. The motor simply won’t start on the next attempt. On the other hand, should the switch remain closed, the motor will start and run. The auxiliary winding will get quickly overheated, and if not detected, or cut out by a protective relay, this winding may cause damage to the main winding due to their proximity.

11. Mention the requirements of air conditioning.

Ans. In this modern age every body is trying to improve his surroundings in order to make living conditions more comfortable. Air conditioning is one of the important contribution in this respect. The technique of maintaining of air condition inside a building in such a way that produces comfort to human beings, ensures trouble free operation of delicate equipment or helps in industrial manufacturing operations is called air conditioning. It involves control of temperature, cleanliness, humidity and circulation of air.

12. What is comfort air conditioning ?

Ans. This is the type of air conditioning whose objective is to produce comfortable and healthy conditions for occupants. In other words, it is the process of treating air so as to control simultaneously the prevailing conditions of temperature, humidity, cleanliness and distribution in the conditioned space to meet the comfort and health requirements of the occupants. It includes the air conditioning of spaces, places and surroundings which are occupied by human beings.

13. Define the effective temperature in air conditioning ?

Ans. An arbitrary index which combines into a single value the degree of sensation warmth or coolness felt by a human body due to the effect of air, temperature, humidity and air movement is called the effective temperature.