J.L.'s Research at IPST

Fundamentals of flow through fibrous media

My early work documented the different permeability properties of paper as a function of flow direction, with relevance to water removal processes such as pressing and drying. Novel experimental methods were developed for measuring both in-plane and transverse permeability components of saturated paper.

This involved computational and experimental analysis of high-intensity drying processes such as "impulse drying," in which a high temperature surface creates high-pressure steam within a wet paper web. The steam pressure can assist in driving liquid water out of the cooler parts of the web. I also pursued research in displacement dewatering, in which directly injected gas can be used to enhance water removal while preserving sheet bulk.

The most exciting aspect of this research was the use of flash x-ray equipment to visualize steam-liquid events in a sheet of paper during a 20 millisecond impulse drying event. At the time, this was the only known peaceful use of flash x-ray technology. Flash x-ray devices are normally used to study the dynamics of bombs, bullets, and other clever devices for killing people. To the best of my knowledge, no one has ever been killed because of my research.

This work was done in collaboration with outstanding colleagues at Georgia Tech, S. Abdel-Khalik and M. Ghiaasiaan. We investigated the fundamentals of flotation deinking hydrodynamics. Flotation deinking is an important process in which fine gas bubbles pass through dilute pulp and selectively remove ink particles, allowing the pulp to be cleaned and prepared for conversion to products such as tissue or writing paper. Our research sought to illuminate the complex interactions of fibers, liquid, and gas in order to find improved methods for design and operation of flotation deinking cells. Gamma densitometry was our primary tool. By measuring the liquid-induced attenuation of a narrow beam of high-energy gamma rays passing through a controlled multiphase flow column, we could document the internal distribution of gas in the pulp slurry and investigate the basic hydrodynamics. This work was a lot of fun!

This work, done primarily by an award-winning Ph.D. student, James Burns, involved a powerful technique for dynamically looking at the internal densification of different layers in a thin, wet web of paper as it is pressed over an interval of 3 to 20 milliseconds. Eddy-current proximity detectors measured the distance to several small, thin copper-mesh targets that were carefully embedded at different layers in a paper web during its formation from a dilute fiber suspension.