<P> x f d, c = concentration entrance length (\ displaystyle x_ (fd, c) = (\ text (concentration entrance length))) </P> <P> D = pipe inside diameter (\ displaystyle (\ text (D)) = (\ text (pipe inside diameter))) </P> <P> R e d = Reynolds Number (\ displaystyle Re_ (d) = (\ text (Reynolds Number))) </P> <P> Sc = Schmidt number (\ displaystyle (\ text (Sc)) = (\ text (Schmidt number))) </P>

For flow in a circular tube as the reynolds number is increased the hydrodynamic entry length