Multistage Evaporator System:

In multistage evaporator system, the refrigerant is utilized to give cooling effect in more than one refrigeration space. It is used while we need to maintain two or more refrigerated spaces at different temperatures & the size of the refrigerated space is such that the setting up of individual refrigeration systems for each one of them is not justified.

  (a) Representation of                                                         (b) T-s Plot of Multistage

Multistage Compression System                                          Compression System

The schematic representation of this kind of system is given in Fig 11(a) along with the equivalent T - S diagram in Fig 11 (b).

First the refrigerant is throttled from state 3-4 and therefore passes into the first evaporator space. Again the refrigerant coming out the evaporator is throttled to a lower pressure & therefore enters the next evaporator (freezer in figure). The refrigerant coming out from the freezer is then compressed in the compressor from state 1 to state 2. The rest of the cycle is same to a simple vapour compression refrigeration cycle.