How valid is Taylor dispersion formula in slugs?


  • Mathieu Sellier University of Canterbury
  • Vi-Vie Ng University of Canterbury



Dispersion, slug, mixing


In a landmark paper, Taylor predicted that shear flow increases the effective diffusivity of species [Taylor, Proc. Roy. Soc. A, 219:186-203,1953]. This paper focused on Poiseuille flow in a circular pipe and predicted the existence of an effective species diffusion much greater than molecular diffusion. The ratio between the effective and molecular diffusion was shown to scale with the square of the Peclet number (product of the pipe diameter with the mean flow velocity divided by the molecular diffusivity). Taylor's study assumed two infinite columns of miscible fluids initially juxtaposed in a pipe and transported by the flow. A question of high practical interest is how valid this prediction is when a finite-sized slug is considered instead of an infinite fluid column. This paper sheds light on the finite-size effects on the mixing of two miscible fluids in a slug and quantifies how accurate Taylor's prediction is for finite length liquid columns. Results show that Taylor's dispersion formula is most accurate for lower Peclet numbers and longer slugs. Results also show that mixing is quite insensitive to the Reynolds number. References
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