Modeling the Flow of a Liquid Droplet Diffusing Into Various Porous Media for Inkjet Printing Applications

Inkjet technology currently relies heavily upon the absorption of ink into porous media. Characterizing the absorption capacity of media as well as the absorption rate can be critical in understanding the entire drying process. Evaluating the absorption performance of a coated medium can particularly be important since the coating may be either semi-absorptive, or in some cases non-absorptive. The absorption performance can also vary among uncoated media. In order to better understand the absorption mechanism, the fluid flow of a water droplet impacting with and diffusing into several porous papers, each with a unique permeability, was analyzed numerically and experimentally in this study. The droplet impact was simulated by computational fluid dynamics techniques for a variety of conditions. The transient computational modeling predicted the shape of the droplet at different time intervals before and after the impact. It also predicted the volume of liquid that had diffused into the porous substrate over time. The results predicted by the computational modeling were then compared to experimental data, which was collected for a real system with the same configuration as in the computational modeling using a high speed digital video camera. The camera captured images of the droplet as it impacted with various coated and uncoated papers. Results showed a relatively good agreement between the computational modeling and experimentation at drop times greater than 0.1 seconds after the impact. A dimensional analysis was also performed on the most effective parameters of the flow process, and a correlation was developed to predict the aspect ratio of the droplet after the impact as a function of the other dimensionless parameters, such as Reynolds and Weber numbers. The results of this study can be useful for drying applications, such as inkjet printing, where absorption of a liquid into a porous medium is critical for the drying process.