Question

A piston cylinder contains gas initially at 3500 kPa with a volume of 0.03 cubic meter. The gas is compressed during a process where pV raise to 1.25 = C to a pressure of 8500 kPa. The heat transfer from the gas is 2.5 kJ. Determine the nonflow work in kj, neglecting changes in kinetic and potential energies.

Answer 1

Initial pressure(p₁)=3500x10³ Pa

Initial Volume (V₁)=0.03 m³

Final pressure(p₂)=8500 x10³ Pa

Gas undergoes a polytropic process given by pV^1.25=constant

Therefore, for process 1-2 we can write,

$p_1 \times {V_1}^{1.25} = p_2 \times {V_2}^{1.25}$

${V_2}^{1.25} =\frac { p_1 \times {V_1}^{1.25} }{p_2}$ =0.01475 m³

The work done during poly tropic process is given by

$W=\frac {p_1 \times V_1-p_2 \times V_2}{n-1}$

$W=\frac {(3500 \times (0.03)-(8500)\times (0.01475)}{1.25-1}$ =-81.5 kJ (-ve sign indicates work done on the gas)

Work done on the gas is W=81.5 kJ