Thermophotovoltaic Generation Research Articles

Enhancement of Radiative Power Using a Divergent Splitter Plate Design in H2–Air Non-Premixed Micro-Combustor

Abstract Micro-combustion based power generation devices can be considered as future alternatives to batteries in miniature electronic devices. Micro-combustors operating in non-premixed mode are free from flashback but face the challenge of properly mixing fuel and air within a small volume. In this work, the effect of a divergent fuel–air splitter design on the mixing performance and combustion characteristics of H2–air fueled diffusion micro-combustor is studied. The laminar reacting flow is simulated using the finite volume method and a detailed hydrogen kinetic mechanism. Three divergent splitter designs are compared with the commonly used rectangular splitter to study the effect on radiation power, an essential parameter for thermophotovoltaic power generation. The best-performing divergent and base rectangular splitter designs are investigated in detail. The study shows that the micro-combustor with divergent splitter design reduces mixing distance (Lmix) by 5–23% depending on inlet velocity and channel height. With the divergent splitter, the peak value of the heat release rate also increases slightly, implying enhanced combustion. The divergent splitter increases the high-temperature surface area of the outer wall as compared to the rectangular splitter. This leads to the micro-combustor with divergent splitter producing significantly higher radiation power (>10%) than the rectangular splitter for larger channel heights and higher inlet velocities.

Optimized design and application performance analysis of heat recovery hybrid system for radioisotope thermophotovoltaic based on thermoelectric heat dissipation

Radioisotope thermophotovoltaic (RTPV) generators face a fundamental challenge, which is the significant output loss and energy wastage caused by the substantial thermal deposition resulting from the arrival of infrared radiation from the heat source at the energy conversion unit. This contradiction has gradually become a key limiting factor for its further development in recent years. In this work, a novel hybrid system based on the thermophotovoltaic-thermoelectric (TPV-TE) effect is proposed, in which the Bi2Te3-based I/W-type thermoelectric leg plays both heat dissipation and heat recovery for power supply. The heat recovery thermoelectric legs were prepared using a cold pressing mould and sintering method, and their Seebeck effect was used to convert the unwanted heat recover from InGaAs thermophotovoltaic cells into electrical power. The design preparation scheme of the heat recovery hybrid module and its potential application performance at 700–1000 K heat source temperature were investigated through experimental tests and simulations. The W-type TPV-TE heat recovery hybrid system exhibits good gain of 12.9% at 1000 K, and the output power can be increased by additional 21.6% in series mode. Simulations for environmental applications show better heat recovery in deep space than on Earth, with an output gain of 63.7% and an energy conversion efficiency of 11.23%. The heat recovery design enhances the competitiveness of the RTPV and provides new ideas for optimizing other heat recovery applications for thermal energy conversion systems.

Experimental Design and Simulation of Radioisotope Thermophotovoltaic Generator by Heating of He⁺ Ion Beam

Experimental Design and Simulation of Radioisotope Thermophotovoltaic Generator by Heating of He⁺ Ion Beam

Irradiation and temperature service stability of the radioisotope thermophotovoltaic generators based general purpose heat source

Highly stable and long-life power supply systems are crucial to the success of space exploration missions. The systematic analysis of the service lives and stability of radioisotope thermophotovoltaic (RTPV) generators with general purpose heat sources (GPHSs) is the cornerstone of future practical space applications. Its operational lifetime is mainly limited by the degradation caused by the irradiation of key transducer components by the isotope source, while its operational stability is mainly related to the temperature variation of the external environment. The irradiation and temperature stability as the main influencing factors of GPHS-RTPV were studied. Results indicate that the output performance of the GPHS–RTPV was maintained at 50.15% after 1 × 1013 n/cm2 neutron and 927.84 Gy γ irradiation. The service life was conservatively estimated to be 19.883 years according to equivalent irradiation experimental results. In addition, the output performance of the GPHS–RTPV fluctuates linearly with temperature, the gradient of Pmax with temperature was −6.7 μW/K·cm2 in a range of 276.5–354.5 K, and higher output at low temperatures. This study explored the lifetime and service stability of GPHS-RTPV under actual operating conditions in space, and lays the foundation for future practical applications.

Module-Level Polaritonic Thermophotovoltaic Emitters via Hierarchical Sequential Learning.

Thermophotovoltaic (TPV) generators provide continuous and high-efficiency power output by utilizing local thermal emitters to convert energy from various sources to thermal radiation matching the bandgaps of photovoltaic cells. Lack of effective guidelines for thermal emission control at high temperatures, poor thermal stability, and limited fabrication scalability are the three key challenges for the practical deployment of TPV devices. Here we develop a hierarchical sequential-learning optimization framework and experimentally realize a 6″ module-scale polaritonic thermal emitter with bandwidth-controlled thermal emission as well as excellent thermal stability at 1473 K. The 300 nm bandwidth thermal emission is realized by a complex photon polariton based on the superposition of Tamm plasmon polariton and surface plasmon polariton. We experimentally achieve a spectral efficiency of 65.6% (wavelength range of 0.4-8 μm) with statistical deviation less than 4% over the 6″ emitter, demonstrating industrial-level reliability for module-scale TPV applications.

Improving the thermophotovoltaic performance of a hydrogen-fueled planar combustor with four-corner inlets via partially inserting porous medium

Micro thermophotovoltaic (TPV) generator is a potentially efficient approach to achieve microscale fuel-to-electricity conversion with high-energy–density, high-efficiency, and small-scale portability, where micro combustor provides the high-temperature continuous combustion process as well as a heat source of thermal radiation. In this study, a hydrogen-fueled planar combustor with four-corner inlets by partially inserting porous medium is proposed and investigated by a three-dimensional numerical model of porous medium combustion with detailed reaction mechanism and local thermal non-equilibrium. The combustor performance with and without partially inserting porous medium under various inlet velocities Vin and equivalence ratios ϕ are compared and analyzed to reveal the inherent strengthening mechanism. Moreover, the effects of various porous parameters on the energy conversion performance are examined: the porosity ɛ, thermal conductivity ks, and porous medium filled volume. The results demonstrate that the inserted porous medium can significantly enhance combustion efficiency, combustor wall temperature and its uniformity, and the largest increase in mean wall temperature reaches 79.7 K at Vin = 9 m/s, resulting in a 35.8 % increase in micro-TPV system efficiency. As ɛ and ks decrease, the combustor energy conversion performance increases while the temperature uniformity decreases. A moderate channel width L = 2.0 mm is good for further improving temperature uniformity and energy conversion efficiency. This study paves the way for the improvement of efficient, practical, and portable microscale generators.

Effect of multihole baffle-induced lobe flow structures on a high efficiency micro-thermophotovoltaic system

For a combustion-based thermophotovoltaic generator (TPV), the baffle-induced reacting flows are numerically investigated in the micro combustor with a multihole baffle representing a mixed feature of bluff body and multiple jets. The lobed flow feature is realized by the momentum difference between fuel and air streams and the baffle wall, not the geometrical conditions like a lobed nozzle. Compared with the H2–air combustor, the lobed flame and the votical structure are enhanced for the CH4–air combustor. To analyze the lobed structure, the lobe intensity and the equivalent perimeter are defined for the stoichiometric mixture line. The maximum lobe intensity is observed at the beginning zone of flame, whereas the equivalent perimeter is increased near the active reaction zone. As the baffle thickness decreases, the lobe structure is enhanced due to the increased vortices. Also, a close relationship between the maximum vorticities at the baffle exit and the maximized lobe structure is observed. The intensified lobe structure contributes to a shorter flame length and more efficient combustion, resulting in increased radiation available for a micro-TPV system. When the lobe structure is enhanced, the high emitter efficiency for an energy conversion device is obtained as 0.319–0.326 for the H2–air combustor.

Reacting flow characteristics based on the axis-switching phenomenon in a baffled micro combustor with rotated noncircular holes for micro-thermophotovoltaic system

• The geometric features related to the axis-switching phenomenon are numerically investigated for a multihole baffled micro combustor. • In the combustor of noncircular holes, secondary flows are more developed. • The flow mixing and combustion efficiency are improved by noncircular air holes. • The best thermal field for a combustion-based TPV system is obtained for baffles with 30°-rotated square holes and 15°-rotated triangular holes. • The emitter efficiency for TPV applications is better than the swirling flow combustor. For a thermophotovoltaic (TPV) generator, a combustor design for strengthening the axis-switching phenomenon is explored. Various simulations based on a Reynolds stress model and detailed chemical mechanism of GRI 3.0 are performed for methane (CH 4 )–air flames in a multihole baffled combustor. The reacting flow fields are investigated with the baffle plates of rotated square and triangular holes. The spreading and merging of multiple air jets past the baffle plate are significantly affected by rotating noncircular air holes. Considering the crossover location changes of the jet half-width, the air jets have a flow structure that quickly generates the axis-switching phenomenon. Compared with the baffled combustor of circular air holes, the center recirculation zone in the combustor of noncircular holes is enlarged by approximately 200% with a hole rotation. As the hole rotation increases, secondary flows become more complicated and the merging of air jets is quickly finished. Based on these flow structures, the region with the stoichiometric condition is observed in various forms of hexagonal, star, circular, and flower shapes. As a result, the flammable region and combustion efficiency are considerably increased. The flame lengths are roughly evaluated as three times the mixing lengths. From the viewpoint of a heat emitter for the TPV application, the heat transfer on the combustion chamber wall is discussed. Compared with the combustor with circular air holes, the combustor with noncircular air holes shows a 5% increase in flammable region and a 5.9% improvement in combustion efficiency. For a combustion-based TPV system, the best uniformity of wall temperature is observed for baffles with 30°-rotated square holes and 15°-rotated triangular holes and the highest mean wall temperatures are obtained when the flame length is approximately 1/3 of the combustor length.

Eco-Friendly and Renewable Power Generation from Heat Using Thermophotovoltaic Technology

Renewable energy sources are the need of the hour, considering climate change’s impact on our planet. Many sources are currently being researched, none of them are commercially stable enough to compete with the existing non-renewable energy sources, with the main reason being performance for the price. We aim to develop a practical system based on the current research progress in infrared-based thermophotovoltaic power generation and storage. Similar systems already exist for harnessing solar energy, but we plan to overcome the inability of solar energy to produce electricity in the absence of sunlight by developing an infrared-based system. Another challenge is the unavailability of enough thermal radiation in the vicinity to support the system from different sources. The main objectives of this work are to identify the advantages and disadvantages of such a system, its feasibility, and its efficiency for working in the real world through theoretical predictions, simulation, and experimentation.

Photonic crystal emitter design and associated efficiency optimization of radioisotope thermophotovoltaic generators

The radioisotope batteries have drawn extensive attention due to the high energy density. Nowadays, the radioisotope thermophotovoltaic systems are one of the most promising radioisotope batteries. In this work, the crystal emitter design and the associated performance of the radioisotope thermophotovoltaic generators are investigated. First, the design of photonic crystal emitter together with the adoptions of both the multi-layer insulation and supporting materials are discussed. In order to optimize the system efficiency, the effects of the area of emitters are mainly investigated. We have analyzed the efficiency of system using GaSb cells and Si cells, respectively. With Si cells, the system efficiency can computationally reach about [Formula: see text] with an output power of 7 W. When GaSb cells are employed, the system performance is estimated to an efficiency of [Formula: see text] with 61.6 W output.

Irradiation and Temperature Service Stability of the Radioisotope Thermophotovoltaic Generators Based General Purpose Heat Source

Irradiation and Temperature Service Stability of the Radioisotope Thermophotovoltaic Generators Based General Purpose Heat Source

Irradiation and Temperature Effect of the Radioisotope Thermophotovoltaic Generators Based General Purpose Heat Source

Irradiation and Temperature Effect of the Radioisotope Thermophotovoltaic Generators Based General Purpose Heat Source

Near-field thermophotovoltaic generation by tuning spectral radiation using a structured emitter and metal-semiconductor-metal cell

Near-field thermophotovoltaic generation by tuning spectral radiation using a structured emitter and metal-semiconductor-metal cell

Investigation of thermal performance and energy conversion in a novel planar micro-combustor with four-corner entrances for thermo-photovoltaic power generators

A novel planar micro-combustor with four-corner entrances is proposed by considering high and uniform outer wall temperature distribution used in micro thermo-photovoltaic generator. For this, a three-dimensional numerical model with detailed chemical mechanism, transport, and heat transfer and a thermo-photovoltaic energy conversion model are developed to examine its performance. Results show that the proposed micro-combustor has excellent wall temperature uniformity because a uniform distribution of high-temperature zones of four individual flames is formed in the combustion chamber. Thermal performance and energy efficiency of the proposed micro-combustor are better than conventional micro-combustor at a low flow rate ( m ) and large equivalence ratio ( φ ). Additionally, the implemented plate-insertion strategy effectively overcome the deterioration of combustor performance under higher m or lower φ . Proposed micro-combustor with plates insertion has the largest wall temperature and energy efficiency, no matter what φ and m are adopted. Plates extend the fluid ravel path and produce some recirculation zones, which promotes heat transfer, preferential diffusion, and flame anchoring, while its pressure loss is larger. Of all the tested cases, the system efficiency reaches a maximum of 6.39%, corresponding to 12.1 W electricity output. This work provides effective combustor design and research insights to develop high-efficiency micro-power system. • A novel micro-combustor with four entrances is proposed for micro-TPV system. • Excellent performance of wall temperature uniformity is obtained. • Inserting plates boosts thermal performance and energy conversion efficiency. • A maximum system efficiency of 6.39% is achieved with 12.1 W electric output.

High-temperature and radiation-resistant spinel-type ferrite coating for thermo-optical conversion in radioisotope thermophotovoltaic generators

High-temperature radioisotope heat source surface coated with excellent performance of thermo-optical conversion coating can greatly improve thermophotovoltaic energy utilization. However, long-term high-temperature and radiation resistance of the thermo-optical conversion pose a great challenge. In this work, spinel-type ferrite thermo-optical conversion coating was proposed to improve the heat and irradiation stability and output power of a radioisotope thermophotovoltaic (RTPV) prototype. Under the continuous irradiation of 32.64 kGy for 24 h at 1400 K, the emissivity of the spinel-type ferrite thermo-optical conversion coating could maintain more than 90%. In addition, the surface morphology of the coating was changed under high temperature, which enhanced its surface emissivity. Spinel-type ferrite thermo-optical conversion coating was applied to the RTPV prototype, which achieved a maximum output power of 144.23 mW. Compared with the RTPV prototype without coating, the overall output increased to 181.51%. Spinel-type ferrite thermo-optical conversion coating showed great application potential in the fields of thermo-optical conversion and high-efficiency utilization of thermal energy.

Evaluation of thermo photovoltaic performance through aluminum-fueled combustor with partially porous medium and different geometric cross-sections

Thermo photovoltaic (TPV) power generation systems have attracted a great deal of attention in the field of portable electronic devices. The high and uniform temperature of TPV combustor plays a decisive role in the improvement of system efficiency. In this study, aluminum is utilized as energy source of TVP. To model the premixed combustion of aluminum-air, an asymptotic model of flame structure including four zones of solid, liquid, and gaseous aluminum and post-flame and three asymptotic fronts of melting, evaporation, and flame is proposed. Then, the conservation equations and boundary conditions are derived and the combustion characteristics of aluminum are obtained. Combustion is evaluated for simple and porous media with trapezoidal, rectangular, triangular, and circular cross-sections. Finally, the influence of parameters on the TVP performance is assessed. The results indicated that in the medium with a porosity factor of 0.8, the total efficiency is higher than the simple medium for all cross-sections. In the medium with a porosity factor of 0.6, however, the triangular and circular cross-sections exhibit lower efficiency compared to the simple medium. In the case with a porosity factor of 0.4, only the efficiency of the channel with a trapezoidal cross-section is higher than the simple medium.

Effects of porosity and multilayers of porous medium on the hydrogen-fueled combustion and micro-thermophotovoltaic

The premixed H2/air combustion with varied porosity of porous medium (PM) is experimentally and numerically studied. The influences of porosity and arrangement of PM as well as the effects of multi-PM-layers on combustion characteristics and energy conversion are comprehensively investigated. The results indicate that a small porosity of porous medium is beneficial to improve flame stability and heat transfer, while it is adverse to the component flow and flame propagation. For the combustor inserted with multi-PM-layers, the larger-small porosities setting balances their opposing effects on the fluidity and the thermal performance, resulting in higher combustion efficiency and radiation temperature. With the increase of flow rate, effects of PM layout and porosity on combustion and heat transfer are remarkably enhanced. Furthermore, the radiation power of the micro thermophotovoltaic (TPV) system is significantly improved with the increase of radiation temperature. It is found that the combustor inserted with three PM layers (porosity p = 0.95 + 0.9+0.85) achieves a high electrical power output and system efficiency, which is more appropriate for the application of micro TPV or micro power generator. It contributes to chemical energy release and heat transmission for further utilization.

Latent Heat Thermophotovoltaic Batteries

Latent heat thermophotovoltaic (LHTPV) batteries are a kind of power-to-heat-to-power storage (PHPS) system that combines very high melting point phase change material (PCM) with thermophotovoltaic (TPV) energy conversion. Electricity is employed to produce the solid-liquid phase transition in the PCM. Consequently, electrical energy is stored in the form of latent heat at very high temperatures (> 1000oC). When needed, stored energy is released as thermal radiation, and converted back to electricity on demand using TPV. Additionally, heat can be also delivered from the cooling of the TPV cells, or directly from the PCM to provide the heating demands. In this study we discuss on the techno-economics of LHTPV systems, focusing on parameters like the round-trip efficiency, the energy-to-power ratio (storage duration), the cost per energy and power capacities, and the levelized cost of storage, all of them depending on the specific selection of PCM and TPV generator. In a purely electrical system, the relatively low TPV conversion efficiency (< 50%) and the low cost of the PCMs (< 4 €/kWh) result in optimal system designs with small power-to-energy ratios, fitting long duration storage application. LHTPV systems delivering also heat can be used for short duration storage applications in fully electrified energy systems where there is heat demand. In all the cases, large-scale LHTPV systems are preferable to minimize the impact of thermal insulation in the total cost of the system. The use of lower melting point PCMs, like FeSiB, enable a significant reduction of the cost per energy capacity, favoring their use in smaller scale applications. On the contrary, higher melting point PCMs, like Si, enable a significant reduction of the cost per power, favoring their use in shorter duration applications. Preliminary experimental results using copper PCM and GaSb TPV cells are provided to illustrate the real operation of a LHTPV system.

Thermal performance improvement of premixed hydrogen/air fueled cylindrical micro-combustor using a preheater-conductor plate

A micro-combustor is the key component of the micro thermo photovoltaic power generation system. The energy conversion efficiency of the system strongly depends on the outer wall temperature and the exergy efficiency of the micro-combustor. A novel preheater-conductor plate was designed to be inserted into a cylindrical micro-combustor to improve the outer wall temperature and the exergy efficiency by preheating premixed hydrogen/air mixture via the preheater plate and conducting out the heat in the combustion chamber via the conductor plate. The impact of the width of preheater plate, the gradually increased and decreased thickness with divergent angle and convergent angle of conductor plate, and the inserted number of conductor plate on the thermal performance of the micro-combustor were investigated. It is found that the gradually varying thickness of the conductor plate has a slight influence on micro-combustor performance compared to other factors. Inserting a preheater-conductor plate with the 0.5 mm-wide preheater plate and the three 0.5 mm-thick conductor plates improve the mean outer wall temperature and the exergy efficiency of the micro-combustor by 173 K and 22.9% respectively. It is indicated that the proposed preheater-conductor plate is capable of considerably improving the thermal performance of premixed hydrogen/air fueled cylindrical micro-combustor.

Thermal Emission‐Enhanced and Optically Modulated Radioisotope Thermophotovoltaic Generators

Infrared radiation generated by high‐energy‐density radioisotope decay can be converted to electrical energy in radioisotope thermophotovoltaic (RTPV) generators. Thermal emission intensity and spectral properties have substantial implications in this thermal energy conversion process. To improve the performance of the RTPV generator, a silicone coating material is used as a thermal emission enhancer, and SiO2 is used as a filter. The silicone coating has excellent thermal emissivity at high temperatures. The SiO2 filter is used for optical modulation during the thermal energy conversion process. The heat transfer optimization problem caused by the internal temperature distribution of the system is discussed. Compared with the experimental model before optimization, the output power of the RTPV generator increased by 126% obtains an open‐circuit voltage of 2.64 V, an electric power of 89.88 mW, and an energy conversion efficiency of 5.62%. The RTPV generator is expected to be a potential candidate for energy supply in extreme environments.