Electrical generator or motor structure – Non-dynamoelectric – Thermal or pyromagnetic
Reexamination Certificate
1999-02-12
2001-01-30
Tamai, Karl (Department: 2834)
Electrical generator or motor structure
Non-dynamoelectric
Thermal or pyromagnetic
Reexamination Certificate
active
06181049
ABSTRACT:
This invention relates generally to thermionic converters containing a multitude of interconnected cells. More particularly, it relates to multiple cell thermionic converters wherein the cells each include a tubular emitter and a tubular collector which are designed for high temperature operation and which are interconnected in series electrical connection by improved annular metal connectors which electrically connect the collector of one cell to the emitter of the next adjacent cell.
BACKGROUND OF THE INVENTION
It has been well known for a number of years to convert heat to electricity through the use of thermionic converters wherein an electron emitter is heated to a sufficiently high temperature so that it emits electrons into the surrounding space where they are received by a juxtaposed electron collector. The electron collector is maintained at a substantially lower temperature than the emitter, and a very low pressure gas, such as cesium vapor, is present in the uniform annular space or gap between the emitter or collector. To increase the overall voltage, a plurality of such cells are appropriately interconnected, i.e. collector of one cell to emitter of the next adjacent cell; an electrical circuit is then completed by connecting an external load to terminals provided on the exterior of the converter.
An early version of such a multiple cell thermionic converter is shown in U.S. Pat. No. 3,702,408 which illustrates a multiple cell thermionic converter wherein a plurality of diodes are stacked on a central heat pipe in a series-connected network of cells within a chamber that contains cesium vapor. The individual cells are interconnected by flexible leads
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made of molybdenum which contain spirally-oriented slots that allow the cesium vapor to reach the gaps between each of the juxtaposed emitter-collector pairs.
Although constructions made in accordance with such design may have been satisfactory for emitters operating at a temperature of about 1700 K, the search has continued for improved electrical connectors particularly for use in thermionic converters that will operate at temperatures in the vicinity of 2000 K, wherein the difference in elongation between the collectors and the emitters can place substantial demands upon designers to accommodate stresses that will be inherently created.
SUMMARY OF THE INVENTION
The invention provides a multiple cell thermionic converter wherein there are a plurality of thermionic cells each including a tubular emitter and a coaxial tubular collector that are juxtaposed and separated by a uniform gap and wherein improved annular metallic connectors interconnect the collector of one cell with the emitter of the next adjacent cell. These annular connectors are apertured in a pattern that effectively reduces the stress that is inherently created in such connectors as a result of thermal expansion and contraction which occurs when the thermionic converter changes from ambient temperature to operating temperature and vice versa, while at the same time providing a low resistance path for current between the two electrodes. The aperture pattern includes a set of slot means which are located in two primary planes oriented substantially perpendicular to the central axis of the connector, which is also the central axis of the thermionic converter. Each set includes one or more slots which extend for a total of at least about 180° of arc in the primary plane, and each slot preferably terminates in a circular opening at each end which is of a diameter greater than the width of the slot itself. More preferably, each slot includes two slot segments of substantially equal length in each respective primary plane. Still more preferably, each of the slot segments is provided with a short, axially oriented, keyhole-like opening at about its midpoint, and auxiliary slots of narrower width are provided in a plane midway between the primary planes. Such keyhole-like apertures and/or auxiliary slots have been found to significantly reduce stress in the annular connectors, which are formed from a suitable refractory metal, while not significantly increasing the resistance of the current path through the connector.
REFERENCES:
patent: 3702408 (1972-11-01), Longsderff et al.
patent: 4667126 (1987-05-01), Fitzpatrick
patent: 5219516 (1993-06-01), Horner-Richardson et al.
Pelessone Daniele
Streckert Holger H.
Fitch Even Tabin & Flannery
General Atomics
Tamai Karl
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