Dynamics of gas bubbles in fiber suspensions

Abstract

The collapse/expansion of a spherical bubble in a Newtonian fluid filled with non-Brownian fibers is numerically investigated. An experimental test was conducted to observe that the spherical geometry of the bubble is maintained during the foaming process. The constitutive equation for the fiber suspension arises from the slender body theory and is coupled with an evolution equation describing the fiber dynamics. First solutions are proposed using steady fiber orientation distributions and the effect of the coupling coefficient on the bubble radius is examined. Later the condition of fixed microstructure is relaxed and the fibers are able to orient along with bubble expansion. Starting with a 3D random orientation, fibers close to the interface orient randomly in planes orthogonal to the radial direction, depending on the level of fiber–fiber interactions. For interaction coefficients encountered in polymer processing, fibers exhibit a closely 2D random planar orientation in a plane tangent to the cavity surface which prevents the bubble to collapse, as observed experimentally.