Performance Characterization of a Heat Pipe Coupled Planar Thermionic Convertor


The performance of heat pipe coupled, planar thermionic energy convertors was characterized using experimental and analytical methods. The experimental current and power characteristics were gathered for two thermionic convertors. Non-destructive failure analysis was performed to evaluate the causes of an inoperable convertor. The experimentation was carried out at the USAF Wright Laboratories while the computer simulations were performed at Wright Labs and the University of Central Florida. The experimentally tested, out-of-core thermionic diodes employ conduction heated emitter electrodes and liquid sodium heat pipe-to-radiator cooled collectors. Cesium vapor is used to produce an interelectrode plasma. A maximum current density of 10.1 A/cm2 and a peak power density of 7.6 W/cm2 were obtained from the Re-Re diode operating in the ignited mode. Non-destructive failure analysis was employed to evaluate the cause of the Mo-Re diode short-circuit. Evaporation of the electrodes and thermal expansion were found to be negligible. The cesium reservoir was heated to vaporize any cesium between the electrodes of the cold diode. The condition of the diode did not change. Both X-ray computed tomography and microfocus radiography were utilized to image the electrode region. The information gathered non-destructively from the diode can be correlated with future destructive investigations. Detailed interior images were limited by X-ray source energy or spacial resolution. A survey was made of thermionic conversion computer programs to evaluate the most effective simulation. A phenomenological model of thermionic conversion was used to simulate the characteristics of the Re-Re thermionic diode. A first principles program, employing a time dependent analysis of plasma parameters, was also examined. There exist no thermionic computer models that produce ignited mode output characteristics in complete agreement with experimental results. The trends predicted by the elementary model, however, compare well with the experimental data.


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Graduation Date





Anderson, Loren A.


Master of Science (M.S.)


College of Engineering


Mechanical and Aerospace Engineering

Degree Program

Mechanical Engineering





Length of Campus-only Access


Access Status

Masters Thesis (Open Access)


Dissertations, Academic -- Engineering; Engineering -- Dissertations, Academic

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