A Study of Flow and Mixing in Bubbly Gas-Liquid Pipe Flow Generated by a Grid

Moghaddas, Jafarsadegh; Trägårdh, C.; Revstedt, J.; Östergren, K.

A Study of Flow and Mixing in Bubbly Gas-Liquid Pipe Flow Generated by a Grid

Document Type : Full article

Authors

Jafarsadegh Moghaddas ¹

C. Trägårdh ²

J. Revstedt ³

K. Östergren ⁴

¹ Chemical Engineering Faculty, Sahand University of Technology, Tabriz, Iran

² Division of Food Engineering, P.O. Box 124, SE-221 00 Lund, Sweden.

³ Division of Fluid Mechanics, P.O. Box 118, SE-221 00 Lund, Sweden

⁴ Division of Food Engineering, P.O. Box 124, SE-221 00 Lund, Sweden

Abstract

The spreading of a tracer in a bubbly two-phase grid-generated turbulent flow system is studied. In this work both particle image velocimetry (PIV) and planer laser-induced fluorescence (PLIF) are used to study the effect of the dispersed phase flow rate on the mixing characteristics of the tracer. The turbulent intensity of the continuous phase in the bubbly two-phase grid-generated turbulent flow is close to isotropic, and increasing the gas void fraction reduces the degree of non-isotropicity. The self-similarity of mean and RMS values of the cross-stream concentration distribution is observed. A new mathematical model is suggested to describe the self-similarity of the cross-stream profiles of the mean concentration based on two separate Gaussian curves into the central and outer region of the flow. The turbulent diffusivity is calculated using the Taylor hypothesis, which is based on the growth of the variance of the cross-stream profiles of the mean concentration, with a position along the direction of the flow. An increase in the void fraction does not affect the diffusivity of the superimposed distribution of the plume in the central region, however it did increase in the outer region.

Keywords

Grid-generated turbulence

Mixing

PIV

PLIF

diffusivity