On the interpretation of some longitudinal dispersion experiments

摘要: Experiments to determine the value of Taylor's longitudinal diffusivity in turbulent flows open channels and circular pipes have produced results which are many cases inconsistent with one another theoretical estimates due respectively Elder (1959) Taylor (1954). Neither is there general agreement on when theory becomes applicable. In an attempt clarify discrepancies two well-known sets experiments by Fischer (1966) (1954) re-examined using a natural procedure which, it argued, has certain advantages over more usual methods. It shown that Fischer's observations channel were not made at sufficient distance downstream from point injection for apply but they consistent description early stages dispersion process Sullivan (1968). subsequently argued these suggest Elder's estimate too low reasons. The first error caused assuming existence eddy calculated means Reynolds analogy second neglect viscous sublayer. On other hand some pipe his theory, although values best fit data about 25% higher than estimate, suggested this same reasons as channel. paper concludes discussion effect sublayer diffusivity. Partly basis approximate model calculations ignore amounts depend Schmidt numbers can be order 20%.