Nitrogen was compressed from initial pressure of 101 kPa to a higher pressure. The respective enthalpies are: 54 kJ/kg and 350 kJ/kg. The compression process is adiabatic and ideal. The volume flow rate is 0.05 m^3/s. Density of Nitrogen before entering the compressor is 1.1 kg/m3 and at high pressure it is 35 kg/m3.

Calculate the work performed by the compressor?

2. Relevant equations

W = m_dot * (h2-h1);

m_dot – mass flow rate in kg/s
h1 = 54 kJ/kg
h2 = 350 kJ/kg

m_dot = Q*rho
Q = 0.05 m^3/s

3. The attempt at a solution

It is easy to plug in the numbers and calculate it, but I am a bit confused about the mass flow rate. When calculating the mass flow rate, do I have use the density at lower pressure or higher pressure and why?