1. The problem statement, all variables and given/known data We have compressed air @ 6 bar and 298 K. This is input to a pneumatic motor (in which pressure energy is converted into kinetic energy) flow rate is 22 L/sec and we get shaft power (1.06 KW) from pneumatic motor as output. And air leaves pneumatic motor @1 bar. Density of air @ 6 bar is 7 Kg/m^3. And we need to find the efficiency of motor. 2. Relevant equations I'm using the Steady Flow Energy Equation (SFEE). So h1 +KE1 +PE1 +Q=h2 +KE2+PE2+W (shaft work) and h= u +pv 3. The attempt at a solution Consider the motor as the control volume Inlet is state 1 and outlet is state 2 State 1- P1=6 bar =600 KPa T1= 298K density= 7 kg/m^3 Q=0.022m^3/s (all above are given) From calculation, mass= Qxdensity=0.154kg State 2- P2=1 bar=100Kpa V2= 0.08 m^3 (for the 0.154kg at the outlet)- after using the adiabatic law i.e. P1(V1^γ)=P2(V2^γ) T2= 178.6 K (from ideal gas equation, after putting (P1xV1)/T1 = (P2xV2)/T2 We neglect the change in KE and PE But in a pneumatic motor, Q=0 and W is given....so how do we find the efficiency???