Question 1.3: An axial flow compressor handling air and designed to run at......
An axial flow compressor handling air and designed to run at 5000 rpm at ambient temperature and pressure of 18°C and 1.013 bar, respectively. The performance characteristic of the compressor is obtained at the atmosphere temperature of 25°C. What is the correct speed at which the compressor must run? If an entry pressure of 65 kPa is obtained at the point where the mass flow rate would be 64 kg/s, calculate the expected mass flow rate obtained in the test.
Since the machine is the same in both cases, the gas constant R and diameter can be cancelled from the operating equations. Using first the speed parameter,
\frac{N_1}{\sqrt{T_{01}}}=\frac{N_2}{\sqrt{T_{02}}}Therefore,
N_2 = 5000 \left(\frac{273 + 25}{ 273 + 18}\right)^\frac{1}{2} = 5000 \left(\frac{298} {291}\right)^{0.5} = 5060 rpm
Hence, the correct speed is 5060 rpm. Now, considering the mass flow parameter,
Therefore,
m_2 = 64 \times \left(\frac{65}{101.3}\right)\left(\frac{298} {291}\right)^{0.5} = 40.58 kg/s