134a refrigerant enters an adiabatic compressor at 140kpa and -10c, the refrigerant is compressed at 0.5kw up to 700kpa and 60c. disregarding changes in kinetic and potential energy. determine: (a) isentropic efficiency (b) the efficiency of the compressor according to the second law consider the environment at a temperature of 27c

(a) 65.04%

(b) 16.91%

Solution:

As per the question:

At inlet:

Pressure of the compressor, P = 140 kPa

Temperature, T = = 263 K

Isentropic work, W = 700 kPa

At outlet:

Pressure, P' = 700 kPa

Temperature, T' = = 333 K

Now, from the steam table;

At the inlet , at a P = 700 kPa, T =:

h = 243.40 kJ/kg, s = 0.9606 kJ/kg.K

At outlet, at  P = 140 kPa, T =:

h' = 296.69 kJ/kg, s' = 1.0182 kJ/kg.K

Also in isentropic process, s = and at 700kPa

(a) Isentropic efficiency of the compressor,

(b) The temperature of the environment, = 273 + 27 = 300 K

Availability at state 1,

Similarly for state 2,

Now, the efficiency of the compressor as per the second law;

= 67.57%