Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter.
Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.
Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.
OCR for page 185
VII
Programmatic Recommendations
The design of successful HEDS systems and components, and decisions concerning alternative designs, will
necessarily be done by the application of computational analysis codes that have been carefully developed and
validated and that are based on physically correct mathematical models. This is true of all modern system
engineering practice and will be especially true for the elaborate systems needed by HEDS. These codes will be
needed at all scales, including those of the smallest components, but in many cases there is insufficient information
available for the development of reliable computational models. Moreover, the data are often costly to obtain at
the gravity levels of interest. For this reason, special attention must be directed toward the design of the experi-
mental test matrices required for model (i.e., code) validation.
All these things being true, these codes and their underlying mechanistic models, even more so than the codes
for aircraft engine analysis and design, for example, must be physically rather than empirically based. This is
because of the need for fidelity in variable-gravity environments and because they must be robust and flexible
enough to credibly evaluate innovative concepts.
NASA research must supply the information needed to build these models and codes, especially that needed
to delineate the ranges of the applicable scaling laws. To ensure progress in developing the desired computational
analysis and design capabilities, such research must clearly in part be directed research based on an evolving
understanding of the programmatic needs. This will be a significant task, requiring patience, commitment, and
careful peer review. In this context, NASA should investigate the possibility of consulting the U.S. Department of
Energy-Naval Reactors program for help in designing research programs that can develop multivariate, physically
based, multiphase computational models.
In the following paragraphs, suggestions are made concerning goals, research planning, and activities of
NASA in support of gravity-related research for HEDS. A number of these recommendations were contained in
the phase I report (NRC, 1997) and are reflected again here, in this more extensive study. It was thought then, and
is still believed, that in view of the long time scale needed for the evolution of basic scientific concepts into
practical applications, the suggested research programs will require a sustained commitment on the part of NASA
to understand gravity-related issues.
185
OCR for page 186
186
MICROGRAVITY RESEARCH
A RESEARCH APPROACH FOR THE DEVELOPMENT
OF MULTIPHASE FLOW AND HEAT TRANSFER TECHNOLOGY
The purpose of this section is to recommend that NASA give consideration to adopting an integrated approach
for the conduct of research on multiphase flow and heat transfer technology for HEDS applications. As pointed
out in earlier discussions of multiphase and heat transfer flow issues, the reliable operation of multiphase systems
and processes in reduced-gravity environments is likely to be required if the HEDS program is to be successful. In
particular, phase-change systems are likely to be necessary for power production, propulsion, and life support.
Unfortunately, relatively little is currently known about the effect of gravity on multiphase systems and processes.
Nevertheless, it is known that the impact can be large (e.g., the flow regimes will be strongly affected).
It should be stressed that the empirical approaches that have been used for the design of multiphase systems
on Earth will not be reliable for space applications. Moreover, it will not be possible to parametrically test in space
the required full-scale multiphase systems and subsystems until a suitable design is achieved. Rather, the approach
recommended in this report is that a reliable, physically based analytical model be developed and qualified against
appropriate terrestrial and microgravity data. The resultant computational model could then be used to analyze
and optimize final designs and to compare the relative merits of various alternate designs (e.g., Rankine vs.
Brayton cycle power plants). Significantly, these analytical models could be used to develop new design features
and to analyze, and support, separate effects experiments and the scale-up of those systems and subsystems that
cannot be tested at full scale in space. Indeed, it is vital that NASA have the capability to scale up data from small-
scale tests if the HEDS research and development program is to be timely and cost-effective.
As is described in Chapter IV, the most detailed and advanced mechanistic models of this type that are
currently available for the analysis of multiphase flow and heat transfer are multidimensional, multifield, two-fluid
computational fluid dynamics (CFD) models. This type of model has been developed by the U.S. DOE-Naval
Reactors program and used by the Navy for numerous applications on Earth. Similar models are being developed
in France (for the Atomic Energy Commission of France) under the FASTNET program (Bestion et al., 1999),
which is focused on nuclear reactor applications. Fortunately, it appears that these models can be extended to
applications involving reduced-gravity environments (Alajbegovic et al., 1999; Lahey and Drew, 2000~.
In order to carry out the various activities that are needed, as described above, to develop a reliable multidi-
mensional, multifield, two-fluid CFD model for HEDS use, a directed program of experimental and analytical
research will be required. The range of specific terrestrial and microgravity data needed to successfully develop
and test the model is unlikely to be obtained in a reasonable time frame without a coordinated, focused effort on the
part of NASA. In particular, careful attention must be paid to understanding and modeling such important
phenomena as flow regimes (including flow-regime transitions), phase distribution, phase separation, multiphase
turbulence, Marangoni forces, boiling/condensing heat transfer, multiphase pressure drop, static and dynamic
instabilities, and condensation-induced loads in reduced-gravity environments. As part of this effort, the dimen-
sionless parameters that characterize the relevant fundamental multiphase phenomena should also be cataloged
and the various distinct operational regimes should be identified.
COORDINATION OF RESEARCH AND DESIGN
Considerable difficulty in the generation of this report arose from NASA's intra-agency organization, in the
sense that outstanding research efforts in some centers were either poorly communicated to groups at other centers
or duplicated the efforts of those other centers. The committee felt that such difficulties were symptomatic of a
counterproductive "territoriality" that has been allowed by NASA senior management to develop and even to
accelerate. Such organizational roadblocks will obviously be detrimental to the implementation of many of this
committee's central research recommendations. The NASA office responsible for microgravity research (presum-
ably the Microgravity Research Division) should diligently inform NASA at large about the issues of reduced
gravity that are foreseen for space hardware design, so that these issues enter design thinking at the conceptual
stage rather than as afterthoughts. Conversely, the microgravity research community should be kept apprised of
design issues whose resolution requires the understanding that would be gained through phenomenonological
OCR for page 187
PROGRAMMATIC RECOMMENDATIONS
187
research. The peer review process is crucial for ensuring the quality of supported research, but that does not
preclude NASA from taking a leadership role in encouraging research on programmatic needs.
NASA should encourage the blending of conceptual design and phenomenological research. Often, phenom-
ena depend strongly on boundary conditions or on the conceptual design of devices, and in such cases it becomes
crucial to involve basic researchers in the development process in a fruitful way. For example, the subject of
fundamental aerodynamics has been developed in close association with aircraft wing design. To accomplish this
melding of research and design is not easy; it requires attentive and sophisticated management.
Equally, communication and coordination among basic researchers and system designers and users will be
essential for HEDS success and should be actively encouraged. For example, problems of bearing and seal
integrity in low or variable gravity suggest a need for novel bearing concepts, which no doubt would raise
significant fundamental research issues. Also, new concepts for flow control devices to replace conventional
valves should be encouraged and pursued through research, in order to provide long-term reliability and to assure
the desired control of dynamic effects in distribution systems.
An especially significant example of the need to connect component development with research concerns
swirling-flow devices intended to provide the centrifugal force needed for phase separations. While the basic
principle of desired operation is understood, device-specific issues of great subtlety will determine success or
failure. Therefore, a variety of configurational concepts should be explored, computationally to the extent fea-
sible. Also, novel concepts for phase separation and mixing by wave processes, oscillations, or flow deflection
should be explored through appropriate research activities.
It is further recommended that the process of gathering and exchanging information relevant to research
directions in support of HEDS missions be strengthened by holding workshops and study groups attended by both
mission technologists and microgravity scientists. The August 1997 workshop at NASA's Lewis Research Center
in Cleveland was just such an endeavor; experts presented a well-organized, ambitious program on the various
activities that are focused on Martian exploration. The program used carefully prepared presentations and work-
shop discussion panels to exchange very useful information. It was a learning experience for the participants and
brought them up to date in a way that could not have been easily done by other means. The committee recom-
mends that workshops of this kind be an ongoing feature of NASA's gravity-related research program. In
particular, workshops should be held, at least biannually, at which technology issues are presented to the scientific
community and relevant microgravity research is presented to the engineering community. Such workshops
should culminate in two types of recommendations: the first type would involve assessment of the applicability of
current research results to the technological issues pertaining to current plans for space exploration; the second
type would focus on definition of future directions for microgravity research in support of the plans for space
exploration. The presentations on both science and technology, along with the recommendations developed,
should be published as a workshop proceedings. The recommendations for the directions of microgravity research
should be reflected in NASA Research Announcements.
It should be emphasized that the goals of HEDS require the development of complex systems that depend on
knowledge from traditionally distinct fields such as biology, fluid physics, and materials science. Such systems
are needed to address life-support needs and in situ resource recovery efforts. Therefore, it is suggested, as it was
in the phase I report (NRC, 1997), that NASA might profitably initiate and support selected interdisciplinary
research projects.
The problem of human bone loss in reduced gravity is clearly an interdisciplinary one and one that must be of
great concern to the microgravity research community. While the dimensions of this problem are uncertain, its
undeniable importance justifies encouragement and support of appropriate research by the microgravity and other
relevant divisions in NASA. Specific research on the physical effects of spacecraft rotation is recommended in
Chapter VI. Beyond that, novel concepts short of spacecraft rotation that might hold promise for countering the
effects of reduced gravity simultaneously for humans and technical devices should be encouraged and pursued.
Furthermore, fluid-mechanical expertise in the microgravity research community may help to explain fundamental
bone-modeling processes, or at least to interpret such processes in relation to proposed countermeasures.
OCR for page 188
188
MICROGRAVITY RESEARCH
MICROGRAVITY RESEARCH AND THE INTERNATIONAL SPACE STATION
It is expected that the International Space Station will provide a unique platform for conducting long-duration
microgravity scientific research and assessing the efficiency and long-term suitability of many of the technical
systems important to HEDS. Unlike previous space shuttle experiments, which by necessity were confined to
component-level tests and typically operated for only a few days, the semipermanent operating status of the
International Space Station will permit testing of integrated hardware systems over time intervals that are long
enough to address critical HEDS system operation requirements. By incorporating hardware systems that are
designed for extended, autonomous operation, critical HEDS technology issues can be addressed, including:
(1) conduct of multiphase flow and heat transfer experiments in support of computational model development;
(2) identification of fundamental channel or system instabilities that are either produced by or modified by
microgravity and the subsequent establishment of appropriate system modifications or control strategies to avoid
or control those instabilities; (3) development of instrumentation and control systems that can tolerate gradual
system degradation and yet respond automatically and appropriately to operational upsets, distinguishing between
instrumentation degradation or failures and actual system failures, while maximizing safety, survivability, and
long-term hardware reliability; and (4) development of the necessary autonomous operational principles that will
be required to automatically shut down and "safe" complicated processing hardware units during serious system
upsets, to serve purposes similar to what is accomplished by methodologies employed currently for spacecraft
computer systems that experience unexpected upsets when they are far from Earth. An example of this type of
opportunity is the development and extended operation of an autonomous water electrolysis system for the
International Space Station that can convert wastewater into oxygen for life support (and hydrogen exhaust).
Development of that system as an advanced, redundant life-support system for the International Space Station will
mean the simultaneous evolution of a key ISRUi processing module that can be used for primary life support on
crowed missions to Mars and for producing oxygen and hydrogen feed gas (for the production of other chemicals)
on the surface of Mars or in the polar regions of the Moon, and for similar HEDS water electrolysis opportunities
on other microgravity surfaces such as asteroids and icy comet cores. The extended operation of systems of this
type in the microgravity environment of the International Space Station is a unique opportunity to subject future
HEDS technology to realistic tests prior to actual deployment. The foregoing comments appeared in the phase I
report (NRC, 1997) and are reiterated here with the added thought that the Space Station will be an especially
important facility for the multiphase flow research program urged earlier in this chapter.
PEER REVIEW FOR REDUCED-GRAVITY RESEARCH
The NASA Research Announcement and peer review mechanisms have been of great benefit to the productiv-
ity and quality of NASA's gravity-related research, as pointed out in the phase I report (NRC, 1997~. These
mechanisms should be maintained as the areas of science and engineering affecting HEDS technologies are further
developed, ensuring the pursuit of truly scientific objectives while enhancing the HEDS enterprise.
REFERENCES
Alajbegovic, A., D.A. Drew, and R.T. Lahey, Jr. 1999. An analysis of phase distribution and turbulence in dispersed particle/liquid flows.
Chem. Eng. Commun. 174:85-133.
Bestion, D., J.-P. Clement, J.-M. Delhaye, P. Dumaz, J. Gamier, D. Grand, E. Herview, D. Lebaigue, H. Lemonnier, C. Lhuillier, J.-R. Pages,
I. Toumi, and M. Villand. 1999. FASTNET: A proposal for a ten-year effort in thermal-hydraulic research. Multiphase Science and
Technology 11:79-145.
Lahey, R.T., Jr., and D.A. Drew. 2000. The analysis of two-phase flow and heat transfer using a multidimensional, four-field two-fluid model.
Proceedings of the Ninth International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-9), October 3-8, 1999.
Nuclear Engineering and Design, in press.
National Research Council (NRC), Space Studies Board. 1997. An Initial Review of Microgravity Research in Support of Human Exploration
and Development in Space. Washington, D.C.: National Academy Press.
In situ resource utilization.
Representative terms from entire chapter:
heat transfer
