Question 6.CSGP.81: A compressor receives 0.1 kg/s R-134a at 150 kPa, -10°C and ......
A compressor receives 0.1 kg/s R-134a at 150 kPa, -10°C and delivers it at 1000 kPa, 40°C. The power input is measured to be 3 kW. The compressor has heat transfer to air at 100 kPa coming in at 20°C and leaving at 25°C. How much is the mass flow rate of air?
C.V. Compressor, steady state, single inlet and exit flow. For this device we also have an air flow outside the compressor housing no changes in kenetic or potential energy.
Continuity Eq.: \dot{ m }_2=\dot{ m }_1
Energy Eq. 6.12: \dot{ m }_1 h _1+\dot{ W }_{ in }+\dot{ m }_{ air } h _3=\dot{ m }_2 h _2+\dot{ m }_{ air } h _4
Ideal gas for air and constant heat capacity: h_4 – h_3 ~ C_{p \text{air}} (T_4 –T_3)
\dot{ m }_{ air }=\left[\dot{ m }_1\left( h _1- h _2\right)+\dot{ W }_{ in }\right] / C _{ p \text { air }}\left( T _4- T _3\right)
=\frac{0.1(393.84-420.25)+3}{1.004(25-20)}=\frac{0.359}{5}
= 0.0715 kg/s
