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Fluid Flow, Heat, and Mass Transfer Fundamentals
^ Effect of Pipe Size in Two-Phase Flow
T. J. Hanratty,* E. Hurlburt, M. Simmons, A. Al-Sarkhi, A. Solermani
U.S. Department of Energy, DE-FG02-86ER13556

The influence of pipe diameter on flow regime transitions and on the modeling of stratified, slug, and annular flows is being studied in inclined and horizontal pipes with diameters of 1 inch, 2 inches, and 4 inches. Accomplishments include the development of a theory to predict the transition from stratified to slug flow, the development of an interpretation of entrainment measurements for annular flow in terms of the fundamental rate processes, the development of an understanding of the wave patterns in stratified flow, the use of photographic and immersion methods to determine drop size in annular flow, and the use of drag-reducing polymers to change flow configurations.

^ Turbulent Flow over Wavy Surfaces
T. J. Hanratty,* Y. Na, S. Nakagawa
National Science Foundation, CTS 92-00936

Turbulent flow over wavy surfaces is being studied both in the laboratory and by a direct numerical simulation. A particular emphasis during the year is the separated region that exists for large-amplitude waves. This well-defined separation bubble is being studied to provide the physical understanding needed to compute and control separated flows. The flow in the separated region is highly three-dimensional and seldom resembles the pattern indicated by the time-averaged streamlines. Work has been initiated to study the effect of waves on heat transfer and the effect of a moving wavy wall.

^ Wall Turbulence
T. J. Hanratty,* Z. C. Liu, Y. Na, S. Nakagawa
National Science Foundation, CTS 92-00936

Laboratory and supercomputer experiments are being used to understand the structure of turbulence close to a wall. Highly organized flows are being identified that are responsible for the sustaining of wall turbulence. The effects of such external influences as structured walls, drag-reducing agents, and micelles on these structures are being studied.

^ Mechanics of Suspensions
J. J. L. Higdon,* M. Viera, Q. Meng
Mobil Corp.

Concentrated suspensions of microscopic particles are encountered throughout the chemical process industry. The goal of this project is to characterize the rheology and sedimentation behavior of these systems, with special attention given to suspensions with nonhydrodynamic interparticle forces and particles of nonspherical shape, such as fibers and platelets. Researchers are developing novel computational algorithms for large-scale many-body simulations to investigate these systems. The methods follow the basic approach of the well-known Stokesian dynamics algorithm, but yield an operational count O(N) as opposed to the O(N3) effort of the traditional approach.

^ Rheology and Structure of Liquid Foams
J. J. L. Higdon,* E. Metsi, M. Talbot
American Chemical Society, Petroleum Research Fund

Liquid-liquid or liquid-gas foams exhibit an interesting range of rheological behavior including yield stresses, wall slip, and stress discontinuities. In addition, the structure and length scales of a foam undergo continuous evolution under the action of shear. The goal of this project is to develop efficient algorithms for the simulation of foam rheology. These algorithms require detailed resolution of the microscopic fluid flows within a large-scale system that captures the disorder and range of length scales present in realistic foam flows.

^ Microchemical Systems
P. J. A. Kenis,* M. Mitchell, S. Thybo
University of Illinois

The objective of this study is to develop microchemical systems in which chemical conversions can take place. Following a rapid prototyping approach based on replica molding, researchers fabricate microscale devices in a variety of materials chosen for compatibility with the conditions and chemistries involved. The research team tries to utilize the distinct properties of fluids at the micro level (such as laminar flow, high surface-to-volume ratio, and enhanced heat transfer) to accomplish chemical processes that are difficult to accomplish at the conventional scale. Possible applications include organic synthesis, micro fuel cells, and catalyst screening.

^ Rheology in a Potential Vortex
W. R. Schowalter,* K. Sarkar
University of Illinois; Monsanto Co.

Vortex flows offer a special flow history for viscoelastic materials because of the revolution of principal axes of strain rate without a corresponding rotation of the fluid. Researchers have computed the pulsating shape of a viscoelastic drop in several vortex flows and have shown how interesting resonance phenomena occur. The results, which relate to the transient stretching of polymers in turbulent flows, offer new insight into the limitations of viscometric measurements.

^ The Free-Jet Behavior of Emulsions
W. R. Schowalter,* K. Sarkar
University of Illinois; Monsanto Co.

Experiments have shown that the diameter of a jet formed from an emulsion of Newtonian fluids exiting from a conduit undergoes a significant expansion. Although qualitatively associated with the relaxation of emulsion droplets to spheres, a quantitative explanation of the jet expansion has been lacking. Through incorporation of boundary integral methods, researchers are showing for the first time the true cause-and-effect relation between emulsion properties and jet expansion.

^ Effect of Free Polymer on Protein Interaction Potentials
C. F. Zukoski,* A. Kulkarni, N. Dixit, A. Mirarefi
National Aeronautics and Space Administration, NAG 8-976

Protein crystals are often produced through the addition of soluble polymers to protein suspensions. In this study, the effects of polymer molecular weight and concentration on the strength of protein interactions is investigated. An unexpected minimum in protein solution second virial coefficient is observed. This phenomenon is intimately related to polymer depletion forces and polymer density fluctuations resulting from the proximity of a polymer solution phase boundary.


Summary of Engineering Research