A laser imaging-LDV coupling measurement of single bubble forming and rising in shear-thinning fluid

The shape evolution of bubble formed in carboxymethylcellulose (CMC) aqueous solution was real-time observed using laser image technique. The flow fields of liquid around growing and rising bubble were measured by laser Doppler velocimetry (LDV), and the liquid mean velocity and its contour curves were obtained. The results show that bubble grows as spherical shape because of the dominant role of surface tension in the early period, and then is stretched gradually as a teardrop shape due to the common effect of buoyancy and shear-thinning of fluid. The axial mean velocity of liquid phase takes on Gaussian distribution with the symmetrical axis passing through orifice center. However, the radial mean velocity increases first and then decreases with the increase of the distance from measured point to the symmetrical axis above. Further, the axial component along symmetrical axis decreases initially and increases with the rise of height, as well as its corresponding contour map diverging gradually. The radial component, yet, decreases steadily with the rise of height, and the maximum value deviates towards the two sides until disappear, as it contour shape of butterfly’s “front wing”.