National Science Foundation     |     Directorate for Engineering  (ENG)
Division of Chemical, Bioengineering, Environmental, & Transport Systems  (CBET)
CBET Award Achievements (Nuggets)
Notable Accomplishments from CBET Awards
CAREER: A Better Understanding of Liquid-Vapor Mixtures
Laura Schaefer    University of Pittsburgh

Background:  Multi-component multi-phase flow systems (liquid-vapor systems in particular) are very common in engineering and industrial applications (such as in boilers, condensers, and nuclear reactors) and in nature (rain and fog).  The importance of these systems has led to the development of many methods and models to study them, so as to improve the systems and processes that depend upon them.  The limitation associated with most of these methods is that they either focus on the very large scale (an overall flow) or a very small scale (a single droplet or bubble, or a flow of a few microseconds).  It is important to be able to bridge this gap, which is possible with the lattice Boltzmann method (LBM).  LBM is a relatively new methodology, and has been applied successfully in simulating fluid flows and associated transport phenomena, but had not previously been able to characterize flows that exhibit a temperature gradient and that include both multiple components (often with widely varying properties) and multiple phases.

Results:  The Schaefer team has developed robust, realistic, and fast computational methodologies for a wide range of multi-component, multi-phase flows.  They have achieved this by modifying and improving the lattice Boltzmann method.  A good metric for evaluating the performance of the method is the range of density ratios that may be modeled.  For single-component flow, the density ratio refers to the two phases, and for multi-component flow it refers to the maximum densities of the two components.  The density ratio of a liquid alloy system is around 1:1, while the density ratio of a liquid water-air system may be around 1000:1.  Prior to Dr. Schaefer's work, the largest possible density ratio that could be reasonably simulated using the lattice Boltzmann method for single-component flow was 40:1, and the largest possible density ratio that could be simulated for multi-component flow was only 2:1.  Dr. Schaefer's group has increased both of these ratios to 1000:1, while also incorporating more realistic thermal behavior (including heating, cooling, condensing, and evaporating flows), as shown in Figure 1.  These transformations in the lattice Boltzmann method mean that it can now be used to better understand and improve a range of applications and phenomena, such as advanced computer chip cooling, groove design for Formula 1 race car tires, and implementation of environmentally-friendly refrigerants.

In order for this work to be applied to a wide range of applications, it is important that the simulations be performed quickly and inexpensively.  Therefore, in addition to the creation of the advanced LBM model for a single processor, the Schaefer team has used the Compute United Device Architecture (CUDA) to expand that model for parallel computation on a graphic processor unit (GPU).  Rather than the typical expensive utilization of supercomputers or multiple PCs linked together in an ad-hoc parallel network, CUDA can achieve comparable (and sometimes better) results using a typical graphics card for a personal computer, at a cost of less than $200.  A three-dimensional simulation (Figure 2) that would take days on a single CPU can be solved in a matter of hours using the new LBM code in conjunction with a GPU.

Scientific Uniqueness:  These unique tools will allow scientists and engineers to bridge the gap between the small time-scale detail of molecular-level simulations, and the large-scale understanding generated by traditional continuum approaches.  These innovations provide us with the ability to model the effect of the interface between phases or components for a range of fluid mixtures.  This will lead to improvements not only in applications involving these mixtures, but will advance our basic understanding of these phenomena.

Laura Schaefer 1
Figure 1.  Temperature and density contours (left) and streamlines (right) for movement of a droplet in a channel with heat transfer and a change in pressure in the x-direction.

Laura Schaefer 2
Figure 2.  Three-Dimensional Simulation of the Velocity and Temperature in a Multi-component, Multi-phase Flow Field
Credit for Figures 1 & 2:  Laura Schaefer and Jie Bao, The University of Pittsburgh
This project addresses the NSF Strategic Outcome Goals, as described in the NSF Strategic Plan 2006-2011, as follows:
Primary Strategic Outcome Goal:      (1) Discovery:  Dr. Schaefer has developed a new computational simulation tool that can realistically model complex physical behaviors.  This tool is beneficial both to the research community, and for a range of engineering applications.
                                                                   (1) Discovery Category:
                                                                          - CAREER:  Faculty Early Career Program
                                                                          - Computer & Information Science Engineering
                                                                          - Engineering Research

Secondary Strategic Outcome Goal:  (2) Learning:  Dr. Schaefer has used the tools and concepts developed through this research to offer a Ph.D. level class in Energetics that addresses the molecular interpretation of thermodynamic equilibrium, partition functions, quantum theory, statistical thermodynamics and gas kinetic theory.  Additionally, she has adapted the laboratory equipment used in this grant to develop experiments that are complementary to the subject matter taught in undergraduate Advanced Thermodynamics and Thermal Systems classes.  Finally, through connections with the undergraduates in the Society of Women Engineers and the American Society of Mechanical Engineers at the University of Pittsburgh, Dr. Schaefer has implemented high school outreach activities to introduce those students to college-level engineering concepts.  These activities have included both visits to the schools and open-house days in Dr. Schaefer's laboratory.
                                                                   (2) Learning Categories:
                                                                          - Undergraduate Education and Undergraduate Student Research
                                                                          - Graduate Education and Graduate Student Research
                                                                          - Postdoctoral Education
                                                                          - Public Understanding of Science and Lifelong Learning
                                                                          - Broadening participation to Improve Workforce Development

In terms of Intellectual Merit, this work is notable because it is the first technique that can robustly capture both small-scale and large-scale velocity, temperature, and pressure effects for multi-phase, multi-component fluid mixtures.  A better understanding of these types of mixtures can lead to more energy-efficient components and systems for a range of applications, and a deeper understanding of the fundamental physics of two-phase flow.

In terms of Broader Impacts, this work is notable because an accurate description of microscale two-phase multi-component fluid behavior can help advance the state of the art for numerous important applications.  These applications can be grouped into three categories:
    (1) small-scale cycles,
    (2) microdevices, and
    (3) large-scale cycles with micro- and mesoscale components.

Small-scale refrigeration cycles can be used for chip cooling, for protective suits in biologically and chemically dangerous environments, as well as for the maintenance of biological samples, transplant organs, and medicine in remote locations.  In microdevices, the ability to accurately characterize interfacial properties can improve the performance of bubble pumps for drug delivery and on-chip chemical analysis.  Finally, in addition to miniaturizing entire refrigeration cycles, directed application of microscale manufacturing techniques can improve cycle performance on the macroscale.  All of these applications can benefit from the improvements in efficiency and the lower costs associated with miniaturized and optimized components.

This research is Transformative.  The results of this research will lead to fundamental advances in our understanding of phase interfaces.  The application of this work will lead to advancements in fields ranging from refrigeration to nuclear power generation.

This research represents Broadening Participation.  The tools developed for this project have been used both by a senior design project team and undergraduate researchers, which included two female and two African-American students.

Existing or potential Societal Benefits of this research:  A better understanding of small-scale, multi-phase, multi-component flows can lead to large increases in the energy efficiency of many common applications, such as heat pumps, computer processors, and refrigerated transport.  This increase in efficiency will lead to lower costs and fewer greenhouse gas emissions.

Program Director:
Theodore Bergman
CBET Program Director - Thermal Transport Processes
NSF Award Number:   0238841
Award Title:
  CAREER: Microscale Two-Phase Zeotropic Flow in Energy Systems
PI Name:   Laura Schaefer
Institution Name:   University of Pittsburgh
Program Element Code:   1406
NSF Investments:
  - American Competitiveness Initiative (ACI)
- Cyber-enabled Discovery and Innovation (CDI)
- Adaptive Systems Technology
CBET Nugget:

  FY 2009

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This Nugget was Updated on 15 September 2009.