1. Refrigeration and Air conditioning

2. Vapour compression refrigeration system

5. Types of vapour compression cycle
Cycle with dry saturated vapour at the entry of compression
Cycle with wet vapour after compression.
Cycle with superheated vapour before compression.
Cycle with superheated vapour after compression
Cycle with undercooling or subcooling of refrigerent.

6. PH and TS diagramVapour entering the compressor is dry saturated

7. TS diagram

8. TS diagram for Cycle with wet vapour after compression.

9. PH diagram for superheated vapour before compression.

10. Effects of superheating
Increases specific volume of suction vapour and due to which decreases capacity.
Increases refrigerating effect.
Increases specific work of compressor.
Net effect is reduced COP due to more increase in compressor work than RE.

11. Subcooling

12. Effects of Subcooling It increases refrigerating effect.
Compressor work remain same therefore increase COP.
It reduces flashing of liquid refrigerent during expansion.
It reduces power per ton for all refrigerents.

13. Difference between dry and wet compression
Dry compression
Wet compression
No liquid refrigerant present.
Superheating required.
Less power required for compressor.
COP is higher for entire system.
Some liquid refrigerant present.
Superheating not req.
More power required for compressor.
COP is lower for entire system.

14. Difference between Ideal and actual vapour compression
Ideal vapour compression
Actual vapour compression
Higher COP.
Vapour leaving evaporator is not superheated.
No heat loss in delivery line.
No pressure drop in condenser and evaporator.
Compression is isentropic.
Lower COP.
Vapour leaving evaporator is superheated.
heat loss in delivery line.
pressure drop in condenser and evaporator.
Compression is not isentropic.

15. Psychrometric properties of air
Dry air : It is a mixture of oxygen (20.91%) and nitrogen (79.09 %) by volume.
Moist air: It is mixture of dry air and water vapour.
Saturated air : Air which have maximum amount of water vapour.
Dry bulb temp.(DBT) : It is temperature of air recorded by ordinary thermometer with clean and dry sensing elements.(td or tdb)
Wet bulb temp.(WBT) : It is temperature of air recorded by thermometer when its bulb is covered with a wet cloth.(tw or twb)

16. Psychrometric properties of air
Wet bulb depression : It is the difference between dry bulb temp. and wet bulb temp.
Dew point temp.: It is the temperature of air recorded by thermometer when the moisture present
in the air begins to condensed.
8. Dew point depression : It is difference between dry bulb temp. and dew point temp. of air.
Specific humidity or Humidity ratio (W) : It is defined as mass of water vapour in unit mass of dry air.
w= mv/ma
Degree of saturation or Percentage humidity (  ) :
It is the ratio of mass of water vapour in unit mass

17. Psychrometric properties of air
of dry air to the mass of water vapour in the same mass of dry air when it is saturated at the same temperature.  = w/ws 11. Relative humidity : It is the ratio of actual mass of water vapour (mv) in a given volume of moist air to mass of water vapour (ms) in the same volume of saturated air at the same temp. and pressure.  = mv/ms 12. Enthalpy of moist air : (H) It is total heat contained in moist air. It is sum of sensible heat and latent heat of moist air.

18. Psychrometric processes
The process of changing and affecting the psychometric properties of the moist air are called psychometric processes. The processes are : 1. Sensible heating 2. Sensible cooling 3. Humidification 4. Dehumidification 5. Heating and humidification 6. Heating and dehumidification

19. Psychrometric processes
7. Cooling and dehumidification 8. Cooling with adiabatic humidification. 9. Adiabatic mixing of two air streams.