(296d) Packed Bed Reactor Experiment: Operating a Two-Phase Reactor Bed in Space

In the early days of developing life support systems for the International Space Station (ISS), NASA recognized a lack of design tools for sizing and operating gas-liquid chemical and biological fixed-bed reactors in the absence of gravity. In fact, one of the first design concepts to treat wastewater resulted in a partial failure of a high temperature catalytic reactor (Holder, et al., 2000). Not long after the initial failures, Prof. Vemuri Balakotaiah and NASA set out to understand and predict the fundamental behavior of cocurrent two-phase flows through porous media in this unique environment (Motil, et al., 2003). The culmination of this research resulted in 3 successful flight experiments on the ISS called the Packed Bed Reactor Experiment (PBRE) (Motil, et al., 2021).

An overview of the evolution of the test hardware, approach to modeling and the results of the PBRE research will be presented including initial drop tower tests, parabolic aircraft tests, and finally the ISS PBRE tests. These experiments included a range of packing size and materials, column diameters, and liquid viscosities. Not only are these results important for life support systems, but they also apply to the development of fuel cells, other chemical/materials processes, and methods to transport nutrients to plants in space. These systems operate differently when in the microgravity environment because the density differences no longer lead to phase separation or “draining” under the body force of gravity. In the absence of gravity, the interfacial or capillary forces play a dominant role in determining the operational parameters such as phase distribution, liquid holdup, and pressure drop which will be discussed. This is most apparent when the liquid inertia and viscous forces are minimal which is common for the space processes mentioned above, i.e. lower liquid flow rates within air/water systems.