This design may provide a reliable, robust method for filling pharmaceutical capsules with fine, dry powders.
Under microgravity, the usual methods of placing granular solids into, or extracting them from, containers or storage vessels will not function. Alternative methods are required to provide a motive force to move the material. New configurations for microgravity regolith storage vessels that do not resemble terrestrial silos, hoppers, or tanks are proposed. The microgravity-compatible bulk-material storage vessels and exitfeed configurations are designed to reliably empty and feed cohesive material to transfer vessels or conveying ducts or lines without gravity. A controllable motive force drives the cohesive material to the exit opening(s), and provides a reliable means to empty storage vessels and/or to feed microgravity conveying lines. The proposed designs will function equally well in vacuum, or inside of pressurized enclosures.
Typical terrestrial granular solids handling and storage equipment will not function under microgravity, since almost all such equipment relies on gravity to at least move material to an exit location or to place it in the bottom of a container. Under microgravity, there effectively are no directions of up or down, and in order to effect movement of material, some other motive force must be applied to the material. The proposed storage vessels utilize dynamic centrifugal force to effect movement of regolith whenever material needs to be removed from the storage vessel. During simple storage, no dynamic motion or forces are required. The rotation rate during emptying can be controlled to ensure that material will move to the desired exit opening, even if the material is highly cohesive, or has acquired an electrostatic charge.
The general concept of this Swirl Action Utilized for Centrifugal Ejection of Regolith (SAUCER) microgravity storage unit/dynamic feeder is to have an effective slot-hopper (based on the converging angles of the top and bottom conical section of the vessel) with an exit slot around the entire periphery of the SAUCER. The basic shape of such a unit is like two Chinese straw hats (douli) — one upside down, on the bottom, and another on top; or two wok-pans, one upright on the bottom and another inverted on top, with a small gap between the upright and inverted pans or hats (around the periphery). A stationary outer ring, much like an unmounted bicycle tire, surrounds the gap between the two coaxial, nearly conical pieces, forming the top and bottom of the unit.
When the entire unit is spun around its axis, centrifugal forces will exceed the cohesive arch strength of the regolith inside (at some rotational speed), and some material will be ejected through the peripheral slot into the surrounding stationary ring. Multiple small brushes or blades will sweep the extruded material around inside the enclosing stationary ring (tire). A circular hole in the outer ring allows the swirling material to pass through the outer ring wall and into an attached screw conveyor or other unit. Because the opening in the outer ring is circular, there is no preferred orientation for an attached screw conveyor, other than that it would work best if its axis lies in a plane tangent to the outer circumference of the ring. The ring and screw conveyor remain in a fixed orientation, while the top and bottom cones of the SAUCER are connected together (with a gap between them) and rotate about their common axis to produce the centrifugal force, enabling the material inside the SAUCER to be ejected through the outer slot or gap into the dispensing ring. The screw conveyor picks up the material swept through the hole in the outer ring.
Without an externally supplied motive force, a cohesive granular solid will not move under microgravity, but will remain in an open container, independent of the container’s orientation, until an external force causes the material to move. The controllable centrifugal force of the proposed SAUCER design provides a rational solution for storage and subsequent emptying of vessels containing cohesive granular solids under microgravity or low-gravity conditions.
This work was done by Otis R. Walton and Hubert J. Vollmer of Grainflow Dynamics, Inc. for Glenn Research Center.
Inquiries concerning rights for the commercial use of this invention should be addressed to NASA Glenn Research Center, Innovative Partnerships Office, Attn: Steven Fedor, Mail Stop 4–8, 21000 Brookpark Road, Cleveland, Ohio 44135. LEW-19016-1