Close-spaced thermionic converters with active spacing control and heat-pipe isothermal emitters

Fitzpatrick, G. O.; Koester, J. K.; Chang, Jia‐Lin; Britt, E. J.; McVey, J. B.

doi:10.1109/iecec.1996.553821

Cited by 9 publications

(5 citation statements)

References 5 publications

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“…Methods to maintain microscale and nanoscale gaps by external means have included external silicon supports [ 54,55,188 ] and micro‐manipulation systems, [ 200,201 ] and active gap control has also been accomplished using piezoelectric translators. [ 83 ] Perhaps the most elegant solution, however, is to use fixed‐form inserts within the gap to define the electrode spacing. This approach has been implemented in several forms, including commercially available micron‐scale grains such as polystyrene particles, [ 202 ] alumina beads, [ 40 ] and silica spheres [ 203 ] ; through lithographically defined insulators such as silicon dioxide or zirconia columns, [ 57,60,204,205 ] quartz standoffs, [ 206 ] and photoresist pillars [ 207,208 ] ; and through freestanding structures such as corrugated ceramic films.…”

Section: Challenges and Recommendationsmentioning

confidence: 99%

“…The devices were able to achieve current and output power densities of A ≈ 5 − 10 Acm −2 and P ≈ 2.5 − 5 Wcm −2 , respectively. [3,[82][83][84] Experimentation with plasma-based TECs was largely discontinued after the twentieth century, due in part to the complexity of plasma engineering and the efficiency limitations of these devices that required them to be operated at very high temperatures. We refer the reader to the previous literature reviews for additional information.…”

Section: Substratementioning

confidence: 99%

“…The devices were able to achieve current and output power densities of

A \approx 5 - 10

Acm −2 and

P \approx 2.5 - 5

Wcm −2 , respectively. [ 3,82–84 ]…”

Section: Historical Researchmentioning

confidence: 99%

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Progress Toward High Power Output in Thermionic Energy Converters

Campbell

Celenza

Schmitt³

et al. 2021

Advanced Science

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Thermionic energy converters are solid‐state heat engines that have the potential to produce electricity with efficiencies of over 30% and area‐specific power densities of 100 Wcm−2. Despite this prospect, no prototypes reported in the literature have achieved true efficiencies close to this target, and many of the most recent investigations report power densities on the order of mWcm−2 or less. These discrepancies stem in part from the low‐temperature (<1300 K) test conditions used to evaluate these devices, the large vacuum gap distances (25–100 µm) employed by these devices, and material challenges related to these devices' electrodes. This review will argue that, for feasible electrode work functions available today, efficient performance requires generating output power densities of >1 Wcm−2 and employing emitter temperatures of 1300 K or higher. With this result in mind, this review provides an overview of historical and current design architectures and comments on their capacity to realize the efficiency and power potential of thermionic energy converters. Also emphasized is the importance of using standardized efficiency metrics to report thermionic energy converter performance data.

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Section: Challenges and Recommendationsmentioning

confidence: 99%

Section: Substratementioning

confidence: 99%

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Progress Toward High Power Output in Thermionic Energy Converters

Campbell

Celenza

Schmitt³

et al. 2021

Advanced Science

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“…2). This design accommodates thermal expansion of approximately 1% that occurs at the typical operating temperatures of 1000°C -2500°C [20], [21], which avoids the complication of active control of the gap spacing [22]. We used a conformal sidewall deposition of poly-SiC to form stiff suspension legs with U-shaped cross sections, which increases the out-of-plane rigidity and avoids contact with the substrate during heating.…”

Section: A Mechanically Robust Suspended Micro-emittersmentioning

confidence: 99%

Microfabricated Thermally Isolated Low Work-Function Emitter

Lee

Bargatin

Vancil

et al. 2014

J. Microelectromech. Syst.

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In this paper, we report low work function mechanically and thermally robust microfabricated thermionic emitters. Conformal deposition of polycrystalline-silicon carbide (poly-SiC) was used to form stiff suspension legs with U-shaped cross sections, which increased the out-of-plane rigidity and helped to maintain a micrometer-scale gap between emitter and collector. The structurally robust poly-SiC suspended structure was coated with a thin tungsten layer to improve adhesion of a work function lowering coating (BaO/SrO/CaO). The measured emitter work function was 1.2 eV and emission current density was >0.1 A/cm 2 , which are promising for applications such as thermionic energy converters.[ 2013-0238]Index Terms-Thermionic emitter, thermionic cathode, energy conversion efficiency, barium coating, barium oxide coating, work function lowering, silicon carbide.

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“…The work proposed by Grover [2] includes theoretical analysis and presents results of experiments carried out on stainless steel heat pipes with a wire mesh wick and sodium, lithium and silver as working fluids. As a result, these devices began to be used in applications such as in rotary heat exchanger [3], waste heat recovery systems in automobiles [4] and in hospitals [5], latent heat storage systems [6][7][8][9], energy storage in wind power systems [10], aeroponic system [11], nuclear reactor [12,13], thermionic converters [14,15], and electronics cooling applications [16]. As a result, these devices began to be used in applications such as in rotary heat exchanger [3], waste heat recovery systems in automobiles [4] and in hospitals [5], latent heat storage systems [6][7][8][9], energy storage in wind power systems [10], aeroponic system [11], nuclear reactor [12,13], thermionic converters [14,15], and electronics cooling applications [16].…”

Section: Introductionmentioning

confidence: 99%

Thermodynamic performance evaluation of an air-air heat pipe heat exchanger

2014

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In this paper, heat transfer analysis for an air-air heat exchanger was experimentally carried out to find its thermal performance and effectiveness. Air-air heat exchanger equipped with finned heat pipes was considered for the experimentation. Mass flow rate of air was considered in between 0.24 to 0.53 kg/s. The temperature at the condenser side of the heat pipe heat exchanger was kept constant at around 23°C and at the evaporator part it was varied from 88 to 147°C. The performance of heat pipe heat exchanger was evaluated at different mass flow rate of air, in terms of effectiveness and compared with its corresponding value found by theoretical analysis.

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Close-spaced thermionic converters with active spacing control and heat-pipe isothermal emitters

Cited by 9 publications

References 5 publications

Progress Toward High Power Output in Thermionic Energy Converters

Progress Toward High Power Output in Thermionic Energy Converters

Microfabricated Thermally Isolated Low Work-Function Emitter

Thermodynamic performance evaluation of an air-air heat pipe heat exchanger

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