# Homework Help: Calculate power in air compression.

1. Apr 22, 2010

### MrNathan

1. The problem statement, all variables and given/known data
In an air compressor air flows steadily at a rate of 15 kg per minute. The air
enters the compressor at 5 m/s with a pressure of 1 bar and a specific volume
of 0.5 m3/kg. The air leaves the compressor at 7.5 m/s with a pressure of 7
bar and a specific volume of 0.15 m3/kg. The internal energy of air leaving the
compressor is 165 kJ/kg greater than that of the air entering the compressor.
The cooling water in the compressor jacket absorbs heat from the air at a rate
of 125 kJ/s. Calculate the power required to drive the compressor.

2. Relevant equations
Q+W=m (mass flow rate)(u2+p2V2+0.5c2^2)-(u1+p1v1+0.5c1^2)

3. The attempt at a solution
Not sure if this is the right equation?

the 1s and 2s should be subtext. after putting i the variables, i got a negative number. should the mass flow rate be a factor of both the brackets or just the first?

thanks