Macroscopic mixing

In the intermediate range of Reynolds numbers, the effects of molecular diffusivity and of macroscopic mixing are approximately additive, and the dispersion coefficient is given by an equation of the form ... 

There is a sharp boundary separating regions in which a > y/(l + y) and the concentration of red phenolphthalein is uniformly equal to x, from regions in which a [Pg.187]

While detailed transport calculations of trace constituent distributions in the troposphere are not generally available, a number of simple box models have been fitted to measurements of seasonal fluctuations in carbon dioxide and ozone and tropospheric distributions of fission debris. These box models may not accurately represent the physical processes responsible for tropospheric motions and mixing, but the parameters used in the model do provide reasonable estimates of macroscopic mixing rates in the troposphere. 

Saffman, P.G. 1960. Dispersion due to molecular diffusion and macroscopic mixing in flow through a network of capillaries. J. Fluid Mech. 7 194-208... 

P. G. Saffman, Dispersion Due to Molecular Diffusion and Macroscopic Mixing in Flow Through a Network of Capillaries, J. Fluid Mech., (7) 194-208,1960. 

Macroscopic mixing mixing of groups or aggregates of molecules, such as... 

Cairns EJ, Prausnitz JM. Macroscopic mixing in fluidization. AIChE J 6 554-560, 1960b. 

Flow fields are broadly classified as either laminar or turbulentto distinguish between smooth and irregular motion, respectively. Fluid elements in laminar flow helds foUow weU-dehned paths indicating smooth flow in discrete layers or laminae, with minimal exchange of material between layers due to the lack of macroscopic mixing. The transport of momentum between system boundaries is thus controlled by molecular action, and is dependent on the fluid viscosity... 

It is an empirical fact that a fluid flowing in a small tube or at low velocity does so by the mechanism of laminar flow, also called viscons, or streamline, flow. The layers of fluid slide over each other with no macroscopic mixing, and the velocity in macroscopic steady flow is constant at any point. At higher velocities flow becomes tnrbulent there is mixing by eddy motion between the layers, and even in overall steady flow the velocity at a point fluctuates about some mean value. 

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