Rheological behavior of alcohol-resistant foam concentrates and its impact on pipe flows

Abstract

The rheological behavior of alcohol-resistant foam concentrates and its impact on pipe flows play critical roles in the scientific design of foam fire-extinguishing systems. In the present work, the equilibrium flow curve, yield stress and thixotropy of alcohol-resistant foam concentrates are experimentally studied, and the effects of the yield stress and thixotropy on pipe flows are theoretically analyzed. The results show that the equilibrium flow curves of alcohol-resistant foam concentrates conform to the Herschel-Bulkley model, and the thixotropic behavior can be well represented by a structural kinetics model that we have established. Ignoring the yield stress or thixotropy of alcohol-resistant foam concentrates will result in an overoptimistic calculated pressure loss in pipe flows. When the thixotropy of alcohol-resistant foam concentrates is incorporated in pipe flow modeling, the nominal shear rate at the pipe wall is no longer a fixed value but gradually increases with time until it reaches a steady-state value. The steady-state value depends on the equilibrium flow curve of the alcohol-resistant foam concentrate and the shear stress at the pipe wall. Based on the initial structural strength and equilibrium flow curve of alcohol-resistant foam concentrates, a method for estimating the design pressure loss in pipe flows is proposed.