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NASA NTRS1999

Surface Tension and Fingering of Miscible Interfaces

Experiments on miscible, buoyantly unstable reaction-diffusion fronts and non-reacting displacement fronts in Hele-Shaw cells show a fingering-type instability whose wavelengths (lambda*) are consistent with an interfacial tension (sigma) at the front caused by the change in chemical composition, even though the solutions are miscible in all proportions. In conjunction with the Saffman-Taylor model, the relation sigma = K/tau, where tau is the interface thickness and K approximately equal 4 +/- 2 x 10(exp -6) dyne, enables prediction of our measured values of lambda* as well as results from prior experiments on miscible interfaces. These results indicate that even for miscible fluids, surface tension is generally a more significant factor than diffusion in interfacial stability and flow characteristics.

Abib, Mohammed↗

NASA NTRS2003

Multiphase flow and phase change in microgravity: Fundamental research and strategic research for exploration of space

NASA is preparing to undertake science-driven exploration missions. The NASA Exploration Team's vision is a cascade of stepping stones. The stepping-stone will build the technical capabilities needed for each step with multi-use technologies and capabilities. An Agency-wide technology investment and development program is necessary to implement the vision. The NASA Exploration Team has identified a number of areas where significant advances are needed to overcome all engineering and medical barriers to the expansion of human space exploration beyond low-Earth orbit. Closed-loop life support systems and advanced propulsion and power technologies are among the areas requiring significant advances from the current state-of-the-art. Studies conducted by the National Academy of Science's National Research Council and Workshops organized by NASA have shown that multiphase flow and phase change play a crucial role in many of these advanced technology concepts. Lack of understanding of multiphase flow, phase change, and interfacial phenomena in the microgravity environment has been a major hurdle. An understanding of multiphase flow and phase change in microgravity is, therefore, critical to advancing many technologies needed. Recognizing this, the Office of Biological and Physical Research (OBPR) has initiated a strategic research thrust to augment the ongoing fundamental research in fluid physics and transport phenomena discipline with research especially aimed at understanding key multiphase flow related issues in propulsion, power, thermal control, and closed-loop advanced life support systems. A plan for integrated theoretical and experimental research that has the highest probability of providing data, predictive tools, and models needed by the systems developers to incorporate highly promising multiphase-based technologies is currently in preparation. This plan is being developed with inputs from scientific community, NASA mission planners and industry personnel. The fundamental research in multiphase flow and phase change in microgravity is aimed at developing better mechanistic understanding of pool boiling and ascertaining the effects of gravity on heat transfer and the critical heat flux. Space flight experiments conducted in space have shown that nucleate pool boiling can be sustained under certain conditions in the microgravity environment. New space flight experiments are being developed to provide more quantitative information on pool boiling in microgravity. Ground-based investigations are also being conducted to develop mechanistic models for flow and pool boiling. An overview of the research plan and roadmap for the strategic research in multiphase flow and phase change as well as research findings from the ongoing program will be presented.

Singh, Bhim S.↗

NASA NTRS1992

Film condensation in a horizontal rectangular duct

Condensation heat transfer in an annular flow regime with and without interfacial waves was experimentally investigated. The study included measurements of heat transfer rate with condensation of vapor flowing inside a horizontal rectangular duct and experiments on the initiation of interfacial waves in condensation, and adiabatic air-liquid flow. An analytical model for the condensation was developed to predict condensate film thickness and heat transfer coefficients. Some conclusions drawn from the study are that the condensate film thickness was very thin (less than 0.6 mm). The average heat transfer coefficient increased with increasing the inlet vapor velocity. The local heat transfer coefficient decreased with the axial distance of the condensing surface, with the largest change at the leading edge of the test section. The interfacial shear stress, which consisted of the momentum shear stress and the adiabatic shear stress, appeared to have a significant effect on the heat transfer coefficients. In the experiment, the condensate flow along the condensing surface experienced a smooth flow, a two-dimensional wavy flow, and a three-dimensional wavy flow. In the condensation experiment, the local wave length decreased with the axial distance of the condensing surface and the average wave length decreased with increasing inlet vapor velocity, while the wave speed increased with increasing vapor velocity. The heat transfer measurements are reliable. And, the ultrasonic technique was effective for measuring the condensate film thickness when the surface was smooth or had waves of small amplitude.

Lu, Qing↗

NASA NTRS1992

The coupling of interfacial instabilities and the stabilization of two-layer annular flows

In this paper the stability of annular pressure-driven parallel flows of two liquids sandwiching a free cylindrical interface is considered. For small to moderate Reynolds numbers, the interface is susceptible to capillary and interfacial wave instabilities, the latter instability caused by a jump in viscosity at the interface. It is shown that favorable velocity profiles in both liquids may stabilize capillary breakup of the interface and suppress the axisymmetric interfacial wave instability. A long-wave analysis leads to the physical mechanism responsible for stabilization of capillary breakup. This physical mechanism is a generalization of that by which capillary breakup is stabilized by interfacial shear in an annular film of a single liquid. Stabilization of intermediate wavelengths is studied with a mechanical energy analysis, which leads to a description of the energetic processes at work.

Dijkstra, Henk A.↗

NASA NTRSDate not supplied

Acoustic Insights into Flow Condensation Mechanisms

Two-phase thermal management systems, with both boiling and condensation processes, offer great potential and heat transfer coefficients that are orders of magnitude higher than traditional single-phase systems. However, two-phase flows can suffer from a wide range of interfacial instabilities leading to significant thermal performance degradation. In this study, we aim to detect regime transitions and characterize dominating physical mechanisms of flow condensation, such as turbulent diffusion in annular liquid film and interfacial waves, using an integrated system of acoustic, modal, and optical sensing techniques and thermofluidic characterizations. A wideband acoustic emissions sensor and high-sensitivity accelerometer are utilized to capture acoustic and vibrational signatures that signal the onset of liquid film formation and interfacial waves during flow pattern transitions. Compared to optical imaging, wideband acoustic emission sensing allows for higher sampling rates to capture high-frequency interface oscillations critical to the flow regime transitions and works well even for condensation in opaque tubes. Acoustic features (e.g., amplitude, frequency, energy, duration) are correlated with thermofluidic processes (e.g., capillary flows, turbulent flows, boiling, condensation). By relating thermal performance metrics with these dynamic signatures in acoustic and modal regimes, we explore the ability to probe and monitor critical flow regime transitions and transport efficiency in flow condensation.

Acoustic Modal Regimes↗

NASA NTRSDate not supplied

Validation of a Two-Phase CFD Model for Predicting Tank Self-Pressurization in the Ground-Based K-Site Experiment

A two-phase CFD model for self-pressurization of a cryogenic storage tank partially filled with liquid hydrogen is presented using the Volume-Of-Fluid approach for modeling two-phase flow, as well as interfacial heat, mass and momentum transfer between the liquid and the vapor regions. The CFD model is validated against self-pressurization experiment performed using the K-site flightweight hydrogen storage tank at NASA Glenn Research Center1. Laminar and turbulent simulations are performed together with conjugated heat transfer analysis. Effects of turbulence, the value of accommodation coefficient used for predicting phase change rates, as well as tank wall geometry are presented and discussed. Predicted tank pressures, fluid and wall temperatures are compared with the experimental data at 49% fill level and two different heat loads for validating this CFD model.

Computational Fluid Dynamics↗

NASA NTRSDate not supplied

Validation of a Two-Phase CFD Model for Predicting Tank Self-Pressurization in the Ground-Based K-Site Experiment

A two-phase CFD model for self-pressurization of a cryogenic storage tank partially filled with liquid hydrogen is presented using the Volume-Of-Fluid approach for modeling two-phase flow, as well as interfacial heat, mass and momentum transfer between the liquid and vapor regions. The CFD model is validated against self-pressurization experiment performed using the K-site flightweight hydrogen storage tank at NASA Glenn Research Center 1 . Laminar and turbulent simulations are performed together with conjugate heat transfer analysis. Effects of turbulence, the value of accommodation coefficient used for predicting phase change rates, as well as tank wall geometry are presented and discussed. Predicted tank pressures, fluid and wall temperatures are compared with the experimental data at 49% fill level and two different heat loads for validating this CFD model.

Computational Fluid Dynamics↗

NASA NTRS1983

Liquid bridges with thermocapillarity

An axisymmetric liquid bridge is subjected to an axial temperature gradient. Thermal variations in surface tension drive a motion that is described using lubrication theory for slender bridges. At leading order in aspect ratio, a class of similarity solutions is obtained valid in the core region away from the endwalls of the bridge. These solutions describe the flows, temperature fields, and interfacial shapes of bridges that may sustain substantial interfacial deflections.

Xu, J.-J.↗

NASA NTRS1990

Thermal buoyancy and Marangoni convection in a two fluid layered system - A numerical study

Thermal buoyancy and surface tension driven convection is numerically investigated in a system with two, immiscible fluids. The geometry investigated, has an open cavity configuration with the lighter fluid situated on top of the heavier fluid, forming a stable layered system. The upper fluid meniscus and the interface are assumed to be flat and undeformable in the calculations. The governing equations and boundary/interface conditions are solved by a control volume based finite difference scheme for two pairs of immiscible fluids; the water-hexadecane system and a so called generic system. The steady state calculations show, that dramatically different flows are predicted when the interfacial tension effects are included or excluded from the system model. These differences are particularly appreciable in surface tension dominated flows, that are typical of microgravity situations. Complex flow patterns, with induced secondary flows are noticed in both the fluids. In general, the overall system heat transfer is found to increase with increases in the thermal buoyancy and surface tension effects, but the behavior of the system flow and thermal fields is not easy to characterize, when different combinations of these forces are considered.

Ramachandran, N.↗

NASA NTRS1999

Fluid Physical and Transport Phenomena Studies aboard the International Space Station: Planned Experiments

This paper provides an overview of the microgravity fluid physics and transport phenomena experiments planned for the International Spare Station. NASA's Office of Life and Microgravity Science and Applications has established a world-class research program in fluid physics and transport phenomena. This program combines the vast expertise of the world research community with NASA's unique microgravity facilities with the objectives of gaining new insight into fluid phenomena by removing the confounding effect of gravity. Due to its criticality to many terrestrial and space-based processes and phenomena, fluid physics and transport phenomena play a central role in the NASA's Microgravity Program. Through widely publicized research announcement and well established peer-reviews, the program has been able to attract a number of world-class researchers and acquired a critical mass of investigations that is now adding rapidly to this field. Currently there arc a total of 106 ground-based and 20 candidate flight principal investigators conducting research in four major thrust areas in the program: complex flows, multiphase flow and phase change, interfacial phenomena, and dynamics and instabilities. The International Space Station (ISS) to be launched in 1998, provides the microgravity research community with a unprecedented opportunity to conduct long-duration microgravity experiments which can be controlled and operated from the Principal Investigators' own laboratory. Frequent planned shuttle flights to the Station will provide opportunities to conduct many more experiments than were previously possible. NASA Lewis Research Center is in the process of designing a Fluids and Combustion Facility (FCF) to be located in the Laboratory Module of the ISS that will not only accommodate multiple users but, allow a broad range of fluid physics and transport phenomena experiments to be conducted in a cost effective manner.

Singh, Bhim S.↗

NASA NTRS2002

The NASA Microgravity Fluid Physics Program: Knowledge for Use on Earth and Future Space Missions

Building on over four decades of research and technology development related to the behavior of fluids in low gravity environments, the current NASA Microgravity Fluid Physics Program continues the quest for knowledge to further understand and design better fluids systems for use on earth and in space. The purpose of the Fluid Physics Program is to support the goals of NASA's Biological and Physical Research Enterprise which seeks to exploit the space environment to conduct research and to develop commercial opportunities, while building the vital knowledge base needed to enable efficient and effective systems for protecting and sustaining humans during extended space flights. There are currently five major research areas in the Microgravity Fluid Physics Program: complex fluids, multiphase flows and phase change, interfacial phenomena, biofluid mechanics, and dynamics and instabilities. Numerous investigations into these areas are being conducted in both ground-based laboratories and facilities and in the flight experiments program. Most of the future NASA-sponsored fluid physics and transport phenomena studies will be carried out on the International Space Station in the Fluids Integrated Rack, in the Microgravity Science Glovebox, in EXPRESS racks, and in other facilities provided by international partners. This paper will present an overview of the near- and long-term visions for NASA's Microgravity Fluid Physics Research Program and brief descriptions of hardware systems planned to achieve this research.

Kohl, Fred J.↗

NASA NTRS2003

The NASA Microgravity Fluid Physics Program: Research Plans for the ISS

Building on over four decades of research and technology development related to the behavior of fluids in low gravity environments, the current NASA Microgravity Fluid Physics Program continues the quest for knowledge to further understand and design better fluids systems for use on earth and in space. NASA's Biological and Physical Research Enterprise seeks to exploit the space environment to conduct research supporting human exploration of space (strategic research), research of intrinsic scientific importance and impact (fundamental research), and commercial research. The strategic research thrust will build the vital knowledge base needed to enable NASA's mission to explore the Universe and search for life. There are currently five major research areas in the Microgravity Fluid Physics Program: complex fluids, niultiphase flows and phase change, interfacial phenomena, biofluid mechanics, and dynamics and instabilities. Numerous investigations into these areas are being conducted in both ground-based laboratories and facilities and in the flight experiments program. Most of the future NASA- sponsored flight experiments in microgravity fluid physics and transport phenomena will be carried out on the International Space Station (ISS) in the Fluids Integrated Rack (FIR), in the Microgravity Science Glovebox (MSG), in EXPRESS racks, and in other facilities provided by international partners. This paper presents an overview of the near- and long-term visions for NASA's Microgravity Fluid Physics Research Program and brief descriptions of hardware systems planned to enable this research.

Kohl, Fred J.↗

NASA NTRS1985

Influence of Melt Convection on Solid-Liquid Interface Under Terrestrial and Reduced Gravity Environments

Solidification and crystal growth processes involve thermal and solutal gradients within a molten phase. In the presence of gravity, such gradients result in convective flows which interact with diffusion fields at the solid-liquid interface. Dendritic growth kinetics was studied in transparent model systems which freeze similarily to most metals. Succinonitrile shows a strong influence of convection at supercoolings below about 1K. Fluid flows adjacent to solid-liquid interfaces and the behavior of shear flows in vertical annular geometries are studied. Novel low-frequency eigenstates were discovered and classified as coupled modes, for their involvement with interfacial deformation coupled to the fluid flow, and are unknown in systems without deformable interfaces. The dependence of coupled convection modes on interfacial geometry, gravity, fluid properties, and transformation characteristics studied for several annual flow arrangements with nominally pure solid-liquid systems.

Glicksman, M. E.↗

NASA NTRS2003

Thermocapillary Convection in Bubbles and Drops

When bubbles or drops are present in an immiscible liquid in reduced gravity and the temperature of the liquid is non-uniform, a thermocapillary stress is generated at the interface due to the variation of interfacial tension with temperature. The resulting flow propels the drop freely suspended in the liquid towards warmer regions, so as to minimize the interfacial energy. In this presentation, we will focus on the effect of convective transport of momentum and energy, that are characterized by the Reynolds number and the Marangoni number, respectively. The results of asymptotic analyses for the speed of the drop for low and large values of these parameters will be discussed. These predictions as well as those from numerical simulations will be compared with reduced gravity experimental results obtained from experiments performed aboard the space shuttle.

Balassubramaniam↗

DOE OSTI2026

Mechanistic mass transfer in hollow fiber membrane solvent extraction for bio-based isobutanol

Membrane solvent extraction (MSE) has emerged as a promising method for selectively recovering bioproducts from complex aqueous streams. Bio-isobutanol, a next-generation feedstock for biofuel, remains challenging to recover because of its low concentration and the presence of inhibitory substances. This study explores the potential of hollow fiber (HF) MSE for bio-isobutanol recovery and systematically examines the coupled effects of fiber packing, shell-side flow dynamics, and aqueous chemistry on performance. A resistance-in-series model is applied to understand mass transfer in the HF MSE modules, quantify local resistances, and validate overall performance. The results show that increasing the fiber packing provides a larger interfacial area but induces poor flow distribution and channeling, hindering effective isobutanol transport. Meanwhile, increasing the shell-side velocity improves isobutanol recovery due to reductions in the boundary layer thickness. The presence of salts, added to mimic fermentation broth, increases the partition coefficient through salting-out effects, further improving isobutanol flux. A modified correlation for the shell-side mass transfer coefficient (k s,ϕ+v ), integrating geometric and hydrodynamic effects, was developed and validated. The proposed model achieves highly predictive accuracy (r 2 = 0.9808) across a wide range of conditions, outperforming previous models. The findings provide mechanistic insight into the interaction of geometric packing, hydrodynamics, and chemistry in governing mass transfer in HF MSE. Overall, this work demonstrates the potential of HF MSE for efficient bio-isobutanol recovery and also provides practical guidelines on critical factors (packing fraction, partition coefficient, and shell-side velocity), aiding in the design and scaling of MSE systems for resource recovery.

Aqueous chemistry↗

NASA NTRS1992

Conservative Grid-Interface Algorithm For Computing Flows

Best features of structured- and unstructured-grid methods combined. Gaps and overlaps between zonal grids eliminated by grid-interface algorithm, which generates single interfacial grid and corrects fluxes of flow quantities accordingly. Incorporated into two three-dimensional Navier-Stokes finite-volume codes and tested in computations of incompressible and compressible flows about simple bodies. Good numerical results obtained. General enough to be incorporated into other finite-volume codes without restrictions on complexities of shapes of bodies and zonal interfaces.

Klopfer, G. H.↗

NASA NTRS1993

On the shear stabilization of capillary break-up of finite liquid bridges

In this paper we consider an isothermal finite liquid bridge under zero-gravity. A sinusoidal interfacial shear stress drives a nonparallel flow in the bridge. The linear stability of this flow to three-dimensional disturbances (which may deform the cylindrical gas-liquid interface) is determined numerically by solving an elliptic eigenvalue problem. Previous results on shear stabilization of capillary break-up of axially unbounded cylindrical interfaces containing a parallel flow are hereby extended to a nonparallel flow. The turning flow regions influence the stability significantly. However, for the particular cases considered, a small area in parameter space remains where the capillary instability is suppressed through interfacial shear. Second, non-axisymmetric oscillatory instabilities are found which originate from an interaction of the interface deformation and the basic flow. These instabilities may be the isothermal limit of the oscillatory instabilities observed in float-zone crystal growth.

Dijkstra, Henk A.↗

NASA NTRS1994

Effects of thermocapillarity on an evaporating extended meniscus in microgravity

An analytical investigation of the effects of thermocapillarity on the flow field within and heat transfer from the extended meniscus region of a heated meniscus which is re-supplied by capillarity is presented. Microgravity conditions are considered. The analysis shows that even for extremely small temperature differences between the wall and the vapor (less than 1 mK) thermocapillary stresses at the liquid-vapor interface due to a non-uniform interfacial temperature drastically alters the flow field. At the same time, these stresses were shown to have only a slight effect on the heat transfer from the extended meniscus but increasing with an increasing temperature difference. Additionally, thermocapillary effects were shown to be sensitive to pore size. A criterion was established from a scaling analysis identifying the conditions necessary for thermocapillarity to affect the operation of capillary-pumped heat transport devices in microgravity. A critical Marangoni number and corresponding critical temperature difference between wall and vapor were identified.

Hallinan, Kevin P.↗