Auburn UniversitySteve R. Duke

Associate Professor of Chemical Engineering

Auburn University

 

Research Interests

 

Research Group

Alumni Research Group

 

Research Summary

Dr. Duke and his students do research in mass transfer, separations, and materials processing. They address problems associated with water quality, wastewater treatment, paper recycling, and materials processing for the environment.

Air-Water Gas Exchange at Waves and Flat Interfaces

Studies seek to discover, characterize, and evaluate physical mechanisms that govern rates of gas absorption across waves and flat interfaces in gas-liquid systems. Laser-induced fluorescence (LIF) techniques are developed and applied to image oxygen concentration boundary layers occurring in tank and wind-wave flow facilities. The LIF systems include nitrogen lasers, high-resolution back-illuminated CCD cameras, and UV-enhanced optics. Digital images allow direct measurement of two-dimensional concentration fields and boundary layer thicknesses for oxygen absorption beneath mechanically generated waves, flat sheared interfaces, and random irregular wind-waves. Results allow sorting out the impact of different interfacial phenomena on air-water exchange rates to determine the mechanisms of transport that are responsible for the 500% enhancement to gas exchange rates that accompanies wind waves. Results from these studies will lead to mechanistic models for gas-liquid transport that will be incorporated into interdisciplinary computer models for global climate and environmental cycles and for ecosystem health for rivers and coastal waters.

Air-Water Gas Exchange at Bubble Interfaces

The goal of this project is to obtain LIF measurements of interfacial concentration fields for gas exchange from bubbles. This new technique is being applied to a classical problem: When a bubble travels through a fluid, how much mass transfer takes place? Present studies seek to measure the concentration fields for oxygen absorption near the surfaces of single bubbles as they rise through oxygen depleted water. The boundary layer thicknesses and concentration gradients can be determined as functions of angular position around the bubble. Experiments provide images and analysis to measure and model the rates of exchange for single bubbles of different sizes. Rising bubbles have a well-documented flow field, offering direct relation of the mass transfer to fluid motions. The LIF results allow characterization and modeling of transfer from bubbles in aeration equipment and spillways, and breaking waves in the natural waters.

Adsorption of Particles at Bubble Interfaces

We have developed techniques for imaging and quantitatively measuring adsorption rates for particle removal at bubble surfaces. Research involves novel bubble-suspending flow facilities and optical techniques to directly image and quantify particle attachment and removal rates for single air bubbles. Studies include removal of inks and stickies from process waters used for cleaning recycled newsprint fibers. The fundamental research goal is to characterize the rates and behavior of the removal of particles (inks and stickies) from water using dissolved air flotation (DAF) and flotation deinking processes. Suspension of the bubble allows particle adsorption and desorption processes at bubble interfaces to be observed dynamically and at high spatial and temporal resolutions while the bubbles and particles are in a flowing field. Results are used to develop criteria for selection and rules for dosage of chemical aids and to characterize models for design and operation of flotation processes.

Development of Materials Substitutes for Hardwood Fibers in Paper Manufacturing

We are developing the new technologies needed in paper processing and agronomy to make fast growing perennial plants viable materials substitutes for hardwood fibers in fine paper manufacturing. Quality paper grades require a blend of long fibers derived from softwood and short fibers derived from hardwoods. Hardwoods are not plantation grown, making accessibility and proper reforestation difficult. Mimosa and giant reed are fast growing perennial plants and our preliminary studies show that these materials produce pulp with qualities similar to that of southern hardwoods. Fundamental and pilot pant scale research focuses on the response of fibers to different pulping processes and to bleaching sequence, the paper properties of fibers in softwood and hardwood blends, propagation and harvesting practice, and genetic improvement.

Research Techniques and Results

One technique uses quenching of laser-induced fluorescence of pyrene-butyric acid to image oxygen concentration boundary layers. Images allow direct measurement of the thickness and behavior of concentration boundary layers along flat and wavy interfaces and around bubbles.

Another technique images and quantitatively measures adsorption rates for ink (particle) removal from wash waters that result from cleaning recycled newsprint fibers.

For results for ink adsorption measurements, click here.

 

 Research Facilities

 

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Last Modified: August 2004