Bubble Behavior And Flow Field Characteristic In Non-Newtonian Fluid

Bubble behavior in non-Newtonian fluids is widely existed in such chemical engineering processes as wastewater treatment, plastic foaming, oil processing, fermentation and polymer devolatilisation. Sodium carboxymethyl cellulose (CMC) and polyacrylamide (PAAm) solutions, two kinds of non-Newtonian fluids, are widely applied in many fields. In this thesis, bubble rising in these two fluids has been investigated.At low gas flow rate, bubble rising velocity in non-Newtonian fluids was measured by laser velocimetry technique. Experimental results reveal that bubbles rise in-line in CMC solution as elliptic sphere shape and oscillationally in PAAm solution as inverse teardrop shape, but fluid viscosity could effectively restrain the track oscillation caused by elasticity. In the process of bubble rising, average bubble volume increases with orifice diameter in CMC solution; however, it directly reverses in PAAm solution. In addition, bubble rising velocity decreases with the increase of concentration, average bubble volume and bubble rising velocity increase with gas flow rate in the two kinds of non-Newtonian fluids.At low gas flow rate, the velocity field in liquid phase around the rising bubble was measured by Laser Doppler Velocimeter (LDV). The mean velocity exhibited characteristic distribution trends in axial and radial directions, respectively. Statistical analysis showed that the momentum transfer between axial and radial directions varied with fluid rheological characteristics. Fourier analysis indicated that in the process of bubble rising, apparent periodical characteristics were displayed in the movements both in gas and liquid phases in CMC solution, and chaotic phenomenon appeared in PAAm solution. Wavelet analysis indicated that shear effect of bubble and fluid rheological characteristics influenced turbulent structure significantly, and coherent structure existed in turbulence. Furthermore, Rescaled Range analysis(R/S analysis) showed that in the experimental conditions, bubble rising in PAAm solution exhibited double fractal characteristics, namely, two persistence dynamics in different extents.