A study on effects of mixing different gases in pipes

A number of studies have been reported regarding gas mixing and replacement phenomena caused by flows within pipes, ever since analysis thereof and tests thereon were introduced by G. I. Taylor. However, conducting tests related to gas mixing and replacement systematically in complex pipes has been difficult, due to several restrictions upon the conducting of such tests posed by real pipe conditions. The study presented here proposes a simulation method based on the results of certain systematic tests on changes in gas concentration resulting from gas mixing and replacement in pipes having complex shapes. Such method involves the combining two fast-response flowmeters built upon different principles of measurement and using an apparatus capable of rapid measurement of changes in density and viscosity caused by gas mixing and replacement. The study results indicate that the gas mixing and replacement phenomena caused by flows in pipes can be expressed approximately by a one-dimensional advective diffusion equation, and that an apparent axial diffusion coefficient can be estimated from a Reynolds number, mean fluid velocity, and pipe diameter in varying flow conditions.