Refrigeration and Air Conditioning | HVAC Interview Question and Answers part 1
Refrigeration and Air Conditioning | HVAC Interview , viva , oral Question and Answers part 1
1. Name four important properties of a good refrigerant
a. Low boiling point
b. High critical temperature & pressure
c. Low sp.heat of liquid
d. Non – flammable and non explosive.
2.. Name some of the equipments used in air conditioning system
a. Filter b. Cooling coil c. Heating coil d. Compressor e. Condenser f. Evaporator
3. Name any four commonly used refrigerants
a. Ammonia (NH3)
b. Carbon di oxide (CO2)
c. Sulphur di oxide (SO2)
d. Freon – 12.
4. What are the factors to be considered in air conditioning a room?
a. Temperature of air
b. Humidity of air
c. Purity of air
d. Motion of air.
5. The door of a running refrigerator inside a room was left open. What will happen?
The room will be gradually warmed up.
6. Differentiate absolute humidity and relative humidity.
Absolute humidity is the mass of water vapour present in one kg of dry air. Relative humidity is the ratio of the actual mass of water vapour present in one kg of dry air at the given temperature to the maximum mass of water vapour it can with hold at the same temperature. Absolute humidity is expressed in terms of kg/kg of dry air. Relative humidity is expressed in terms of percentage.
7. What is effective temperature?
The effective temperature is a measure of feeling warmth or cold to the human body in response to the air temperature, moisture content and air motion. If the air at different DBT and RH condition carries the same amount of heat as the heat carried by the air at temperature T and 100% RH, then the temperature T is known as effective temperature.
8. What is binary vapour cycle? What are the advantages of that cycle over other cycles?
Binary vapour cycle is a cycle in which two cycles are combined together to get higher overall efficiency. The advantages are, the overall thermal efficiency is increased and the thermal energy is utilized at high temperature.
9. What are the fluids used in the topping cycle of the binary vapour cycle?
Mercury, Sodium, Potassium and mixture of sodium and potassium.
11. What are the disadvantages of mercury as the vapour used in topping cycle?
- The minimum operating temperature of the cycle is very high
- It is highly toxic and the cost is high
- Economically on attractive due to higher initial cost.
12. State the unit for refrigeration and any two properties o good refrigerant.
Unit of refrigeration is expressed in terms of tonne of refrigeration (TR). A tonne of refrigeration is defined as the quantity of heat required to be removed form one tonne of water at 0oC to convert into ice at 0oC in 24 hours.
Properties: Low boiling point, High critical temperature
13. What is dew point temperature?
The temperature at which the vapour starts condensing is called dew point temperature. It is also equal to the saturation temperature at the partial pressure of water vapour in the mixture. The dew point temperature is an indication of specific humidity.
14. Name the important properties of a good refrigerant.
a. Low boiling point
b. High critical temperature
c. High critical pressure
d. Low specific heat of liquid
e. High COP
f. Non toxic, safe and Eco-friendly.
15. Represent the following psychrometric process using skeleton psychrometric chart?
a. Cooling and dehumidification
b. Evaporative cooling.
16. What is meant by adiabatic saturation temperature (or) thermodynamic wet bulb temperature?
It is the temperature at which the outlet air can be brought into saturation state by passing through the water in the long insulated duct (adiabatic) by the evaporation of water due to latent heat of vapourisation.
17. What is psychrometer?
Psychrometer is an instrument which measures both dry bulb temperature and wet bulb temperature.
18. What is psychrometric chart?
It is the graphical plot with specific humidity and partial pressure of water vapour in y axis and dry bulb temperature along x axis. The specific volume of mixture, wet bulb temperature, relative humidity and enthalpy are the properties appeared in the psychrometric chart.
19. Define sensible heat and latent heat.
Sensible heat is the heat that changes the temperature of the substance when added to it or when abstracted from it. Latent heat is the heat that does not affect the temperature but change of state occurred by adding the heat or by abstracting the heat.
20. What is meant by adiabatic mixing?
The process of mixing two or more stream of air without any heat transfer to the surrounding is known as adiabatic mixing. It is happened in air conditioning system.
21. What are the important psychrometric processes?
a. Sensible heating and sensible cooling,
b. Cooling and dehumidification,
c. Heating and humidification,
d. Mixing of air streams,
e. Chemical dehumidification,
f. Adiabatic evaporative cooling.
22. Define psychrometry.
The science which deals with the study of behaviour of moist air (mixture of dry air and water vapour) is known as psychrometry.
23. Name few commonly used refrigerants
Ammonia, Carbon dioxide, HFC134a, HCFC22, HC blend, water and R407C
24. What is the function of throttling valve in vapour compression refrigeration?
The function of throttling valve (Expansion valve) is to allow the liquid refrigerant under high pressure and temperature to pass at controlled rate after reducing its pressure and temperature.
25. In a vapour compression system where the lowest and highest temperatures occur?
Lowest temperature: at evaporator inlet&Highest temperature: At compressor outlet
26. Why air cycle refrigeration is more popular in aircraft air-conditioning?
a. Lower equipment weight
b. Utilizes the porting of the cabin air
27. What are the merits and demerits of air refrigeration system?
- The refrigerant air is cheap and easily available
- There is no danger of fire of toxic effects due to leakages.
- The equipment weight to tonne of refrigeration is low
- The quantity of refrigerant used per of refrigeration is high.
28. What are the various methods to produce refrigeration?
a. By melting of a solid
b. By sublimation of solid.
c. By evaporation of liquid
29. What are the various components in vapour absorption system?
Absorber, Generator, Solution pump and Expansion valve
30. Name some important refrigeration applications
Ice making, food preservation, milk processing, industrial air-conditioning, chemical related industries, medical and surgical aids, oil refining and treatment of metals.
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