Correlations between air drag and movement of water droplets in fibrous media

Abstract

The movement of dispersed liquid drops in fibrous media occurs in many industrial applications, such as in filtration of liquid aerosols. The process can be complex and challenging to model for predictive purposes in filter design. Often the industry relies upon experimental comparisons between filter media to determine suitable media for specific applications. Correlations for predicting drop behaviors, such as drop movement and coalescence, in filter media can reduce experimental efforts by providing a tool to estimate media performances that narrows the range of media for experimental comparison.This work in this paper focused on movement of drops due to the drag force of the flowing gas phase. A simple force balance and introduction of drag coefficient led to a correlation for estimating the drag coefficient for the average movement of drops in fiber media. Experiments were conducted to detect the movements of water drops and parameters fitted to the correlation. Experimental observations showed that the drops did not move until the drag force exceeded a minimum. A correlation was developed to relate the Reynolds number of the gas flow through the porous medium that caused the drop to move.The minimum Reynolds number correlation provides a prediction of the size of drops that can be expected to move in a fiber medium for a given flow rate of gas. The drag coefficient correlation provides for a calculation of the average velocity of the moving drops through the fiber medium. The correlations are limited to motions of single drops and do not account for other drop behaviors such as coalescence or channel flow. This work extends prior works that developed similar correlations for drops on single fibers and on surfaces of fiber mats.