Microwave heating in a vacuum centrifugal concentrator

A vacuum centrifugal concentrator comprising

• an enclosure having an open top and a lid for closing said top, a vacuum vessel of a conductive metal, the vessel having a rim disposed in said enclosure with the lid forming an airtight seal with the rim, the lid including a frame comprised of frame parts defining quarter wave microwave traps,
• a microwave energy absorbing glass piece supported by the frame with a metal screen covering at least one surface of the glass piece, the lid frame embodying ferrite microwave absorber means thereon,
• a row of microwave seal strips carried on the frame parts for sealing said enclosure against microwave leakage,
• a centrifugal rotor rotatably supported within an interior of said vacuum vessel, there being a well depending from a bottom of said vacuum vessel, the rotor including a shaft extending from the rotor into said well,
• a magnetic drive coupling element carried in said well and connected to a lower end of said shaft, an upper end of the shaft being received in a metallic rotor hub, there being a shaft support bearing and housing therefor encircling the shaft intermediate the shaft upper and lower ends, the rotor hub and bearing housing increasing shaft effective diameter to decrease shaft length/diameter ratio and correspondingly the tendency of the shaft to act as a microwave antenna,
• another power-driven magnetic coupling element disposed externally of said well and cooperating with the first-mentioned magnetic coupling element for rotating said rotor,
• the bottom of the vacuum vessel including a series of slots disposed therein in an annular course located radially exterior of the well,
• a microwave generator for injecting microwave energy into the vacuum vessel,
• an air-filled waveguide disposed at a lower surface of the vessel bottom for distributing the microwave energy within said vacuum vessel, the waveguide having a beginning end coupled to the microwave generator and a terminal opposite end for terminating microwave energy flow, the waveguide intermediate said beginning and terminal ends thereof having a circular plan portion, the waveguide being mounted to the bottom of the vacuum vessel and having a series of slots therein in correspondence to and aligned with the slots in the vessel bottom, said slots being progressively larger in size in a direction away from the waveguide beginning end, with the slots in the vessel bottom being substantially larger in size than those in the waveguide, and
• a dielectric ring intervening the waveguide and the vacuum vessel bottom lower surface for sealing the slots in the waveguide from the corresponding slots in the vessel bottom,
• said dielectric ring including bosses extending through the vacuum vessel slots and upwardly a distance from the vessel bottom, the bosses including means defining hollows therein, the hollows being open to the air in the waveguide.