Packed Bed Reactor Experiment (PBRE) - 04.09.15
The Packed Bed Reactor Experiment (PBRE) studies the behavior of gases and liquids when they flow simultaneously through a column filled with fixed porous media. The porous media or “packing” can be made of different shapes and materials and are used widely in chemical engineering as a means to enhance the contact between two immiscible fluid phases (e.g., liquid-gas, water-oil, etc.). Packed columns can serve as reactors, scrubbers, strippers, etc. in systems where efficient interphase contact is desired, both on Earth and in space. Science Results for Everyone
Information Pending Experiment Details
NASA Glenn Research Center, Cleveland, OH, United States
ZIN Technologies Incorporated, Cleveland, OH, United States
Sponsoring Space Agency
National Aeronautics and Space Administration (NASA)
Earth Benefits, Scientific Discovery, Space Exploration
ISS Expedition Duration
March 2015 - Ongoing
Previous ISS Missions
None. ^ back to top
- Currently, there are no design methodologies for two-phase flow in packed beds in microgravity. Consequently, two-phase flow equipment for space applications cannot be optimally designed, leading to excess weight; unnecessary energy consumption; and reduced operational life.
- Results provide engineers with principles to design more efficient equipment for heat/mass transfer in space. The impact of this research is scientific, technological and economic.
- Scientifically and technologically, knowledge gained from PBRE studies allows for more optimally designed equipment for chemical and/or biological reactors to be used in, for example, water recovery, planetary surface processing and oxygen production. Availability of this equipment permits planners to conceive longer duration space missions not currently possible. On the economic side, optimal designs are lighter and more efficient, thus leading to savings in launch mass, energy use and maintenance costs.
A basic understanding of two-phase flows through porous media is of interest in many chemical and biological processing systems as well as many geophysical applications. NASA technologies include adiabatic two-phase flows or two-phase flows with heat transfer that are relevant to life support systems, fuel cells, in-situ resource utilization, heat pipes, materials processing, production of pharmaceutical grade water, and transport of nutrients in soils. A very important unit operation that involves gas-liquid flow through porous media is the fixed Packed Bed Reactor (PBR). Examples of current space systems in which a fixed PBR is used include the Volatile Removal Assembly (VRA), the Integrated Advanced Water Recovery System (AWRS), and IntraVenous Water GENeration system (IVGEN). NASA is currently operating systems with packed bed reactors for ground and flight-based testing with an incomplete understanding of how the reduced gravity environment affects the performance and reliability of these reactors. This is especially critical when gas-liquid flows are involved. The expected outcome of this research effort is to develop a set of guidelines and tools to enable engineers to reliably design and operate packed bed reactors for microgravity as well as the lunar and Martian environments.
Existing approaches for predicting the flow regimes and pressure drop for gas-liquid flow through a PBR are valid only for 1 g, and are based on liquid (or gas) holdup within the bed. Initial microgravity tests conducted in the reduced gravity aircraft and drop tower clearly show that the liquid holdup is significantly influenced by gravity. Furthermore, most of these models have only been verified using the "trickle flow" regime which does not exist in microgravity. Basic hydrodynamic models developed specifically for reduced gravity have been partially validated within the constraints of aircraft and ground facilities. However, typical flow ranges used for real systems require up to several minutes to develop fully which is far beyond the time scales available for ground tests. In addition, instabilities and hysteresis effects that may exist require long testing durations to establish new operating conditions. Thus, testing on the International Space Station (ISS) is required for complete validation of the semi-empirical models.
Flight experiments can provide critical hydrodynamic information for a project with a broader scope which includes reduced gravity aircraft and ground-based (1 g) experiments. The main objective of the overall project is to develop and validate macroscopic equations that can be used in partial and microgravity conditions to accurately predict flow pattern transitions; pressure drops; and mass transfer rates in chemical and biological reactors in which gas-liquid flows occur through randomly packed beds. The hydrodynamic investigations addressed in the Packed Bed Reactor Experiment (PBRE) focus on the transitions between flow regimes (e.g., bubbly-to-pulse flow transition) and the associated pressure gradients over the range of relevant operating regimes of the PBRs (e.g., liquid and gas flow rates, particle sizes, and fluid viscosities). These design tools provide a fundamental understanding of these phenomena in low gravity.^ back to top
Water-recovery systems, fuel cells and other equipment on the International Space Station use packed bed reactors, but currently none are designed to handle both liquid and gas at the same time. With improved understanding of how packed bed two-phase flow works in microgravity, scientists are be able to design more efficient, lightweight thermal management and life support systems that use less energy, benefiting the Space Station and future lunar and Mars missions.
Design rules for gas-liquid flows through packed columns are well developed on Earth (i.e., for normal gravity) but lacking for reduced or zero gravity. The Packed Bed Reactor Experiment seeks to fill this knowledge gap by studying the hydrodynamics of gas-liquid flows in zero gravity through packed columns. By understanding how gravity affects gas-liquid flows through packed columns (or packed beds, as they are known in the industry) better, more predictive correlations for pressure drops and flow regime maps can be developed with the proper gravity-dependent terms included.
Crew member involvement is required for initial installation and setup for the experiment. Additional time is required to change out test sections or hard drives. All operational functions will be controlled from ground. Near-real time downlink is required to verify proper experimental operation; review camera zoom, aperture and focus settings; and to determine new test conditions. The minimum set of data to downlink includes the gas and liquid flow rates; test section temperature and pressure, and a single NTSC video feed. Uplink data include information to revise controllable test conditions based on evaluation of test results. No telerobotics are required.
Crew member installs and sets up the PBRE equipment in the MSG work volume, and also is needed to change out test sections or hard drives. All experimental operations are then controlled by the ground science team. Downlink between test runs is needed to verify proper experimental parameters such as camera zoom, aperture and focus settings, and test conditions. Test results are evaluated and data are sent from ground to revise controllable test conditions. Once the experiment is completed crew involvement is needed to disassemble the equipment and safeguard data storage hardware for return to ground.
Information Pending^ back to top
Ground Based Results Publications
Motil BJ, Balakotaiah V, Kamotani Y. Gas-Liquid Two-Phase Flows Through Packed Beds in Microgravity. American Institute of Chemical Engineers Journal. 2003 Mar; 49(3): 557-565. DOI: 10.1002/aic.690490303.
Revankar ST, Olenik DJ, Jo D, Motil BJ. Local Instrumentation for the Investigation of Multi-Phase Parameters in a Packed Bed. Proceedings of the Institution of Mechanical Engineers, Part E: Journal of Process Mechanical Engineering. 2007 November 1; 221(4): 187-199. DOI: 10.1243/09544089JPME142.
Packed Bed Reactor Experiment inside the Materials Science Glovebox work volume. (NASA Image)
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Packed Bed Reactor Experiment test section. (NASA Image)
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This video frame capture shows a pulse flow in the microgravity airplane. The frames should be read from the top down, and show the pulse front (seen as the leading edge of a "lighter" region in the image) advancing from left to right. Pulse flows are desired in packed bed reactors because they enhance inter-phase contact --thus making the process more efficient. (NASA Video Capture)
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