Session: 7.6 - Experimental methods for multiphase flows

Paper Number: 170093

170093 - Rheology of Aqueous Foam in Multiphase Forming: An Experimental Approach 

Abstract: 

Using aqueous foam instead of water as a carrier fluid for cellulose fibers has emerged as an innovative approach to reduce water consumption and energy usage in manufacturing fiber-composite products such as paper, tissue, and board.  High density (HD) foam contains about 40% to 75% air in the form of small air bubbles ranging from 40 to 200 microns in diameter.  In addition to reduced water and energy consumption, there is another important advantage in using HD foam instead of water.  The air bubbles prevent fiber-fiber interaction and entanglement, resulting in a much more uniform fiber composite formation and a better quality product.  This use of aqueous foam necessitates the study of the fluid dynamics of HD foam in the presence of cellulose fibers. The current study explores the flow behavior of HD foam with and without fibers with an air content in the foam that ranges from 50% (that is, bubbly liquid) to 85% (that is, wet foams). Foams are classified into bubbly liquid, wet foams, and dry foams based on their air content [1].  Although the rheology of HD foam has been measured by rheometers, the rheology in pressure-driven flow systems varies based on the pressure and the volume of the air content.  In other words, as the flow passes through a higher to lower pressure field, the volume of the air content changes due to air compressibility, resulting in varying rheology.   We have developed an experimental system that can be used to measure the rheology of HD foam, considering the change in pressure based on the differential pressure measured over a length of one meter. The measured differential pressure is used to provide the wall shear stress. To account for the non-Newtonian nature of the foam, the Weissenberg-Rabinowitsch correction method is applied to calculate the true shear strain rate. Using these parameters and the volume equalization method, the viscosity of foam is obtained as the ratio of the wall shear stress to the true shear strain rate. Furthermore, the Herschel-Bulkley model is applied to analyze the experimental results, allowing the calculation of the consistency index and flow behavior index based on the true shear strain rate and the calculated viscosity. The analysis provides rheological properties of aqueous foam with and without the presence of fiber. In addition to a better understanding of the HD foam rheology in pressure-driven systems, the results can also be used to develop transparent fluids with the same rheological behavior as HD foam; this is the only way that transitions from laminar to turbulent flow can be detected using optical diagnostics methods such as particle-image velocimetry.

1. Tuomo Hjelt, Jukka A. Ketoja, Harri Kiiskinen, Antti I. Koponen, Elina Pääkkönen Foam forming of fiber products: a review Journal of Dispersion Science and Technology, 43:10, 14622-1497.

Presenting Author: Sarvesh Shukla Georgia Institute of Technology

Presenting Author Biography: