Gas dispersion in transitional flow through a straight tube

• Main Author: Flint, Leonard Frederick
• Published: Imperial College London 1968
• Subjects: 542
• Online Access: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.623019

Longitudinal dispersion of gas has been studied in two straight tubes of length 24m. and diameters 0.684 cm and 2.77 cm. respectively. Responses to pulse stimuli were recorded with a katharometer. Flowing Nitrogen was traced by Ethylene, Argon or Helium, to study the effect of Schmidt number over the transition from laminar to turbulent flow. Results are presented for 200< Re< 10⁴, and a theoretical study of dispersion has been made for the whole turbulent regime. For Re < 500 results confirm the Taylor—Aris solution for the dispersion coefficient, DL. For larger laminar Reynolds numbers results in the small tube showed better agreement with the theory than in the larger one. Dispersion in turbulent flow was in general described by a single dispersion coefficient. Values of the dispersion parameter (DL/ūd) were higher than predicted by theory (up to Re = 10⁴) and showed less variation with Schmidt number. Over a small region in the transition regime, response curves could not be described fully by a single dispersion coefficient because they were asymmetrical. This phenomenon has been analysed qualitatively in terms of a proposed model of transitional flow, involving intermittent slugs of turbulence, and the resulting secondary flow patterns.