Knudsen's equation

Knudsen's equation

[kə′nüd·sənz i‚kwā·shən]
(physics)
An equation for the amount of gas that flows through a tube in free molecule flow, q √(2π)Δ pd 3/6 l √(ρ), where q is the volume of gas measured at unit pressure that flows through the tube per second, Δ p is the difference between the pressures at the ends of the tube, d is the inside diameter of the tube, l is the length of the tube, and ρ is the density of the gas at unit pressure.