# How to calculate the flow rate of a gas through a pipe?

I am trying to calculate the flow rate of Nitrogen through a cylindrical pipe.

I only need a ballpark value, and the only information I have is the inlet pressure as 15 psig (assuming the same pressure throughout the pipe, so there is no pressure drop), the pipe diameter as 6" and material which is stainless steel.

I tried applying Bernoulli and Poiseuille's equations but I since there is no pressure drop and I do not have a pipe length I am unsure how to use these equations.

• Friction will cause a pressure drop.... – Solar Mike Jan 27 at 18:14
• Yes but I am trying to simplify the calculation because I only need a rough number. Is there a formula I can use that does not use pipe length and pressure drops? – eenz Jan 27 at 18:17
• Search on here, one of many : engineering.stackexchange.com/q/8004/10902 – Solar Mike Jan 27 at 18:22
• If there is no pressure drop, there will be no flow. I think the 15 psi implies that the inlet side is 15 psi above the ambient pressure, or pressure at the outlet giving you a 15 psi differential. Then use the equations linked from @solarmike – jko Jan 27 at 18:36
• Flow rate is determined and governed by pressure drop. Consider a huge pipe and low flow, pressure drop is insignificant. But a very small pipe will result in a large pressure drop and prevent flow (like sucking a malt through a thin straw). Flow in a pipe is modeled based on pipe surface and size, inlet and outlet pressure, and fluid viscosity. – Tiger Guy Jan 27 at 20:01