A fluidized bed reactor was developed in-house at the NASA Glenn Research Center for use in reduced-gravity environments for space exploration applications such as life support and in situ resource utilization. On Earth, fluidized particle beds are established through the balance of an upward fluid flow (and its resultant drag force) and gravity’s downward pull on the bed particles. In the novel reactor concept, a swirling flow was used to stabilize a radial fluidized bed in microgravity experiments conducted in Glenn’s 2.2 Second Drop Tower. Specifically, the fluidized bed was formed through a balance of the radial drag (from an inward flow) and apparent centrifugal forces acting on the bed particles. Gravitational settling dominated the particle behavior in comparison normal-gravity tests.
Fluidized bed reactors are advantageous in chemical processing for reasons including rapid mixing, liquidlike behavior, resistance to temperature fluctuations, and high heat and mass transfer rates. Given these benefits, NASA had begun evaluating such reactors for filtration, the reduction of lunar regolith to produce oxygen, and the pyrolysis or incineration of solid waste to recover valuable resources during long-duration outpost missions. However, the function of these reactors in reduced-gravity environments had generally not been evaluated.
Numerical simulation of the flow field within the reactor, illustrating the region of low axial and radial velocity along the reactor wall and between the two injection ports (top center of figure), where the particle bed is stabilized in microgravity.
In the cylindrical reactor concept developed at Glenn, the air (or other fluid) is tangentially injected at the reactor wall and is exhausted through a porous tube out the ends of the reactor. This configuration creates an inwardly swirling flow with a zone of low axial and radial velocity along the reactor wall between the injection ports. In the experiments conducted, two injection ports were symmetrically located at each end of the reactor vessel (which was internally 9.2 cm in length and 10 cm in diameter). A fluidized bed of zirconium silicate particles (which were nominally 0.2 to 0.3 mm) was stabilized in microgravity experiments. The same airflow conditions, where the apparent centrifugal and gravitational accelerations were of similar order, were insufficient to maintain the radial bed in normal Earth gravity. As expected from the numerical simulation of the gas flow, the microgravity particle bed formed at the middle of the reactor length because of the stagnation region at the symmetry plane. With increasing particle loads, the bed was observed to spread axially toward the ends of the reactor. The exploratory study of this reactor concept has been completed.
Microgravity end-view photograph showing the white swirl-fluidized particle bed along the reactor wall, while the center of the reactor is nearly particle free.
Stocker, D., et al.: Effects of Gravity on Swirl-Stabilized Fluidized Beds. AIAA-2006-1136, 2006.
Glenn contacts:
Dennis P. Stocker, 216-433-2166, Dennis.P.Stocker@nasa.gov
John E. Brooker, 216-433-6543, John.E.Brooker@nasa.gov
Authors:
Dennis P. Stocker, John E. Brooker, and Dr. Uday G. Hegde
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Last updated: December 14, 2007
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