STANDARD VAPOUR COMPRESSION CYCLE

The standard vapour compression refrigeration cycle would consist of the following:

(a) Low pressure saturated vapor would enter the compressor.

(b) Compression would be isentropic.

(c) Constant pressure heat rejection would occur at the condenser with the exit state of the refrigerant being saturated liquid.

(d) The throttling process would be adiabatic.

(e) Constant pressure heat transfer would take place in the evaporator.

The T-S plot above shows the working of such a system. Here, the dry saturated working medium at state 1 is compressed isentropically to state 2. Constant pressure heat transfer occurs from state 2 until the compressed vapor becomes saturated liquid or condensate at state 4. The compressed vapor is next throttled from the high pressure region in the condenser (state 4) to the low pressure region in the evaporator (state 5). Since throttling is an irreversible process, it is represented by a broken line. After throttling to evaporator pressure, the heat transfer in the evaporator causes vaporization of the working m>1)

= 0 - (h2-h4) + (h1-h5) = -(h2-h1) where the negative sign indicates that work is done on the system in order to execute the cyclic process.

COP = net refrigerating effect/|work done| = (h1-h4)/(h2-h1)