Question

Refrigerant-134a enters an adiabatic compressor as saturated vapor at -24°C and leaves at 0.8 MPa and 60°C. The mass flow rate of the refrigerant is 1.2 kg/s. Determine (a) the power input to the compressor and (b) the volume flow rate of the refrigerant at the compressor inlet.

Answer 1

Refrigerant-134a is compressed steadily by a compressor. The power input to the compressor and the volume flow rate of the refrigerant at the compressor inlet are to be determined. 

Assumptions:

1. This is a steady-flow process since there is no change with time.
2. Kinetic and potential energy changes are negligible.
3. The device is adiabatic and thus heat transfer is negligible.

Properties: From the refrigerant tables (Tables A-11 through 13)

Analysis:

(a) There is only one inlet and one exit, and thus \(\overset •m_1 = \overset •m_2 = \overset •m\). We take the compressor as the system, which is a control volume since mass crosses the boundary. The energy balance for this steady-flow system can be expressed in the rate form as

(b) The volume flow rate of the refrigerant at the compressor inlet is

\(\overset • V_1 = \overset •mv_1\)

= (1.2kg/s)(0.17395 m³/kg)

= 0.209 m³/s