fig 7.1 content of this post
In this post we are going to discuss different methods of improving vapour compression cycle and its COP lets start. Following are the types of improvement in vapour compression cycle:
1. Improvement by adding Flash Chamber.
2. Improvement by adding Accumulator.
3. Improvement by Subcooling of liquid refrigerant by using vapours of refrigerant. 
4. Improvement by Subcooling of liquid refrigerant by using Liquid refrigerant.

1. Improvement by adding flash chamber:
Fig 7.2 improvement by adding flash chamber
During the expansion process some unwanted vapours are generated. This unwanted vapour is totally inactive to absorb latent heat in evaporator.
In flash chamber there are baffle plate on which mixer from expansion device strikes and there is separation of vapour and liquid.
Unwanted vapour is directly supplied to compressor where as only liquid is supplied to Evaporator. By adding flash chamber there is no effect on refrigerating effect. Work supplied to compressor remains constant and COP remains constant. The effect obtained is only reduction in evaporator length of pipe.
Flash chamber is added between expansion device and evaporator. Flash chamber is an insulating tank. When there is fixed load on our vapour compression cycle then flash chamber is added in the plant.

2. Improvement by adding Accumulator:
Fig 7.3 Improvement by adding accumulator
An accumulator is an insulated tank which is installed in between the expansion device and evaporator. Figure shows block diagram of this system.
Unwanted vapour generating during expansion process are strikes on baffle plates. The evaporator also supply’s the mixture of liquid and vapour when load on evaporator is less. This mixture also strikes on the baffle plate.
In accumulator separation of liquid refrigerant and vapour refrigerant is carried out. Accumulator supplied only liquid to evaporator. It also supplied only vapour to compressor. When load on our vapour compression cycle varies then accumulator is added in the system.

3. Improvement by Sub-cooling of liquid refrigerant by using vapours of refrigerant:
Fig. 7.5 Fig 7.4 improvement by vapour refrigerant 
Sub-cooling of liquid refrigerant is carried out by using vapour of refrigerant. The heat exchanger is installed between condenser and expansion device. In heat exchanger through one pipe of liquid at 45 degree C flowing where another line vapour refrigerant at -10 degree  C are flowing. 
Liquid rejects its heat energy to vapour refrigerants and sub-cooling of liquid takes place. Which improves COP of plant. 

 4. Improvement by Sub-cooling of liquid refrigerant by using liquid refrigerant:
Fig 7.4 improvement by liquid refrigerant
In this method subcooling of liquid refrigerant is carried out by using liquid refrigerant. A heat exchanger is installed in between condenser and expansion device. 
One line carries liquid refrigerant of 45 degree C whereas another line carries liquid refrigerant of -10 degree C temperature. This liquid is taken partially from after expansion. The heat transfer takes place, if heat exchanger liquid of 45 degree C gives heat energy to partial -10 degree C. 
After absorbing heat energy liquid at -10 degree C.evaporates and it is directly supplied to compressor.