80 Matching Results

Search Results

Advanced search parameters have been applied.

Final report for Frequency selective surfaces for rugged thermophotovoltaic emitters

Description: Ion Optics created an array of regularly spaced holes in a thin conductive surface film on a dielectric substrate. When heated, this pattern behaved as a selective emitter, with more than 50% of total radiation in a well-defined peak with a center frequency determined by geometrical spacing. Peak wavelength did not alter with change in temperature, and materials easily survived 10 hours at 1000 C in air. The selective emitter will increase efficiency of thermophotovoltaic power converters.
Date: April 5, 2001
Creator: Daly, James
Partner: UNT Libraries Government Documents Department

Design considerations for a thermophotovoltaic energy converter using heat pipe radiators

Description: The purpose of this paper is to discuss concepts for using high temperature heat pipes to transport energy from a heat source to a thermophotovoltaic (TPV) converter. Within the converter, the condenser portion of each heat pipe acts as a photon radiator, providing a radiant flux to adjacent TPV cells, which in turn create electricity. Using heat pipes in this way could help to increase the power output and the power density of TPV systems. TPV systems with radiator temperatures in the range of 1,500 K are expected to produce as much as 3.6 W/cm{sup 3} of heat exchanger volume at an efficiency of 20% or greater. Four different arrangements of heat pipe-TPV energy converters are considered. Performance and sizing calculations for each of the concepts are presented. Finally, concerns with this concept and issues which remain to be considered are discussed.
Date: June 1, 1997
Creator: Ashcroft, J. & DePoy, D.
Partner: UNT Libraries Government Documents Department

A novel design for monolithic interconnected modules (MIMs) for thermophotovoltaic (TPV) power conversion

Description: The design for the fabrication of Monolithic Interconnected Modules (MIMs) for thermophotovoltaic (TPV) power conversion described in this paper utilizes a novel, interdigitated contacting scheme that increases the flexibility in the size of the component cells and hence the output current and voltage of the module. This flexibility is gained at the expense of only minimally increased grid obscuration. Because the design uses the grid fingers of the component cells as the interconnect structure, the area of the device used for this purpose becomes negligible. In this paper the authors report on the specifics of the design as well as issues related to the fabrication of the modules. Preliminary performance data for representative modules also are offered.
Date: June 1, 1997
Creator: Ward, J. S.; Duda, A. & Wanlass, M. W.
Partner: UNT Libraries Government Documents Department

Segregated tandem filter for enhanced conversion efficiency in a thermophotovoltaic energy conversion system

Description: A filter system to transmit short wavelength radiation and reflect long wavelength radiation for a thermophotovoltaic energy conversion cell comprises an optically transparent substrate segregation layer with at least one coherent wavelength in optical thickness; a dielectric interference filter deposited on one side of the substrate segregation layer, the interference filter being disposed toward the source of radiation, the interference filter including a plurality of alternating layers of high and low optical index materials adapted to change from transmitting to reflecting at a nominal wavelength {lambda}{sub IF} approximately equal to the bandgap wavelength {lambda}{sub g} of the thermophotovoltaic cell, the interference filter being adapted to transmit incident radiation from about 0.5{lambda}{sub IF} to {lambda}{sub IF} and reflect from {lambda}{sub IF} to about 2{lambda}{sub IF}; and a high mobility plasma filter deposited on the opposite side of the substrate segregation layer, the plasma filter being adapted to start to become reflecting at a wavelength of about 1.5{lambda}{sub IF}.
Date: December 31, 1996
Creator: Brown, E.J.; Baldasaro, P.F. & Dziendziel, R.J.
Partner: UNT Libraries Government Documents Department

SMALL OIL BURNER CONCEPTS BASED ON LOW PRESSURE AIR ATOMIZATION

Description: The development of several novel oil burner applications based on low pressure air atomization is described. The atomizer used is a prefilming, airblast nozzle of the type commonly used in gas turbine combustion. The air pressure used can be as low as 1,300 Pa and such pressure can be easily achieved with a fan. Advantages over conventional, pressure-atomized nozzles include ability to operate at low input rates without very small passages and much lower fuel pressure requirements. The development of three specific applications is presented. The first two are domestic heating burners covering a capacity range 10 to 26 kW. The third application presented involves the use of this burner in an oil-fired thermophotovoltaic power generator system. Here the design firing rate is 2.9 kW and the system produces 500 watts of electric power.
Date: March 16, 2000
Creator: BUTCHER,T.; CELEBI,Y.; WEI,G. & KAMATH,B.
Partner: UNT Libraries Government Documents Department

A tube-in-tube thermophotovoltaic generator

Description: A thermophotovoltaic device includes at least one thermal radiator tube, a cooling tube concentrically disposed within each thermal radiator tube and an array of thermophotovoltaic cells disposed on the exterior surface of the cooling tube. A shell having a first end and a second end surrounds the thermal radiator tube. Inner and outer tubesheets, each having an aperture corresponding to each cooling tube, are located at each end of the shell. The thermal radiator tube extends within the shell between the inner tubesheets. The cooling tube extends within the shell through the corresponding apertures of the two inner tubesheets to the corresponding apertures of the two outer tubesheets. A plurality of the thermal radiator tubes can be arranged in a staggered or an in-line configuration within the shell.
Date: December 31, 1996
Creator: Ashcroft, J.; Campbell, B. & Depoy, D.
Partner: UNT Libraries Government Documents Department

High-performance, lattice-mismatched InGaAs/InP monolithic interconnected modules (MIMs)

Description: High performance, lattice-mismatched p/n InGaAs/lnP monolithic interconnected module (MIM) structures were developed for thermophotovoltaic (TPV) applications. A MIM device consists of several individual InGaAs photovoltaic (PV) cells series-connected on a single semi-insulating (S.I.) InP substrate. Both interdigitated and conventional (i.e., non-interdigitated) MIMs were fabricated. The energy bandgap (Eg) for these devices was 0.60 eV. A compositionally step-graded InPAs buffer was used to accommodate a lattice mismatch of 1.1% between the active InGaAs cell structure and the InP substrate. 1x1-cm, 15-cell, 0.60-eV MIMs demonstrated an open-circuit voltage (Voc) of 5.2 V (347 mV per cell) and a fill factor of 68.6% at a short-circuit current density (Jsc) of 2.0 A/cm{sup 2}, under flashlamp testing. The reverse saturation current density (Jo) was 1.6x10{sup {minus}6} A/cm{sup 2}. Jo values as low as 4.1x10{sup {minus}7} A/cm{sup 2} were also observed with a conventional planar cell geometry.
Date: October 1, 1998
Creator: Fatemi, Navid S.; Wilt, David M.; Hoffman, Richard W., Jr.; Stan, Mark S.; Weizer, Victor G.; Jenkins, Phillip P. et al.
Partner: UNT Libraries Government Documents Department

Lapped substrate for enhanced backsurface reflectivity in a thermophotovoltaic energy conversion system

Description: A method is described for fabricating a thermophotovoltaic energy conversion cell including a thin semiconductor wafer substrate having a thickness ({beta}) calculated to decrease the free carrier absorption on a heavily doped substrate; wherein the top surface of the semiconductor wafer substrate is provided with a thermophotovoltaic device, a metallized grid and optionally an antireflective (AR) overcoating; and, the bottom surface (10 ft) of the semiconductor wafer substrate is provided with a highly reflecting coating which may comprise a metal coating or a combined dielectric/metal coating.
Date: December 31, 1996
Creator: Baldasaro, P.F.; Brown, E.J.; Charache, G.W. & DePoy, D.M.
Partner: UNT Libraries Government Documents Department

The development and testing of emissivity enhancement coatings for thermophotovoltaic (TPV) radiator applications

Description: One requirement of a thermophotovoltaic (TPV) radiator is to efficiently emit photons at high temperatures to TPV cells for conversion to electric power. Because many candidate radiator materials with adequate structural properties display low emissivity, coatings or other surface modifications are required for enhancement of emissivity. Six plasma sprayed coatings and one textured surface demonstrated adequate thermal stability and emittance values of 0.8 or greater. Promising attributes of modified surfaces are identified.
Date: March 1, 1999
Creator: Cockeram, B.V.; Measures, D.P. & Mueller, A.J.
Partner: UNT Libraries Government Documents Department

Double opposite-end tubesheet design for a thermovoltaic energy converter

Description: A method and apparatus are disclosed for the direct conversion of energy by thermovoltaic energy conversion having first and second tubesheets, at least one photon emitter plate secured to and extending from the first tubesheet, at least one cold plate secured to and extending from the second tubesheet, a plurality of thermovoltaic cells disposed along oppositely disposed exterior surfaces of the cold plate, and means cooperating with the tubesheet for maintaining a vacuum between the photon emitter plate and the cold plate.
Date: December 1, 1997
Creator: Ashcroft, John M.; Campbell, Brain C. & DePoy, David M.
Partner: UNT Libraries Government Documents Department

Spectral utilization in thermophotovoltaic devices

Description: Multilayer assemblies of epitaxially-grown, III-V semiconductor materials are being investigated for use in thermophotovoltaic (TPV) energy conversion applications. It has been observed that thick, highly-doped semiconductor layers within cell architectures dominate the parasitic free-carrier absorption (FCA) of devices at wavelengths above the bandgap of the semiconductor material. In this work, the wavelength-dependent, free-carrier absorption of p- and n-type InGaAs layers grown epitaxially onto semi-insulating (SI) InP substrates has been measured and related to the total absorption of long-wavelength photons in thermophotovoltaic devices. The optical responses of the TPV cells are then used in the calculation of spectral utilization factors and device efficiencies.
Date: December 31, 1997
Creator: Clevenger, M.B. & Murray, C.S.
Partner: UNT Libraries Government Documents Department

A thermophotovoltaic energy conversion device

Description: A thermophotovoltaic device and a method for making the thermophotovoltaic device are disclosed. The device includes an n-type semiconductor material substrate having top and bottom surfaces, a tunnel junction formed on the top surface of the substrate, a region of active layers formed on top of the tunnel junction and a back surface reflector (BSR). The tunnel junction includes a layer of heavily doped n-type semiconductor material that is formed on the top surface of the substrate and a layer of heavily doped p-type semiconductor material formed on the n-type layer. An optional pseudomorphic layer can be formed between the n-type and p-type layers. A region of active layers is formed on top of the tunnel junction. This region includes a base layer of p-type semiconductor material and an emitter layer of n-type semiconductor material. An optional front surface window layer can be formed on top of the emitter layer. An optional interference filter can be formed on top of the emitter layer or the front surface window layer when it is used.
Date: December 31, 1996
Creator: Charache, G.W.; Baldasaro, P.F. & Egley, J.L.
Partner: UNT Libraries Government Documents Department

Analysis of TPV Network Losses (a Presentation)

Description: This talk focuses on the theoretical analysis of electrical losses associated with electrically networking large numbers of TPV cells to produce high power TPV power generators.
Date: December 8, 2004
Creator: DePoy, DM; Dashiell, MW; Rahner, DD; Danielson, LR; Oppenlander, JE; Vell, JL et al.
Partner: UNT Libraries Government Documents Department

Production data on 0.55 eV InGaAs thermophotovoltaic cells

Description: Low bandgap 0.55 eV (2.25 {micro}m cutoff wavelength) indium gallium arsenide (In{sub 0.72}Ga{sub 0.28}As) thermophotovoltaic (TPV) cells use much more of the long wavelength energy emitted from low temperature (< 1,200 C) thermal sources than either Si or GaSb cells. Data are presented on a statistically significant number (2,500) of these TPV cells, indicating the performance obtainable in large numbers of cells. This data should be useful in the design and modeling of TPV system performance. At 1.2 A/cm{sup 2} short-circuit current, an average open-circuit voltage of 283 mV is obtained with a 60% fill factor. The peak external quantum efficiency for uncoated cells is 65% and is over 50% from 1.1 to 2.2 {micro}m. Internal quantum efficiency is over 76% in this range assuming an estimated 34% reflectance loss.
Date: May 1, 1996
Creator: Wojtzuk, S.; Colter, P.; Charache, G. & Campbell, B.
Partner: UNT Libraries Government Documents Department

Materials and process development for the monolithic interconnected module (MIM) InGaAs/InP TPV cells

Description: Four major components of a thermophotovoltaic (TPV) energy conversion system are a heat source, a graybody or a selective emitter, spectrum shaping elements such as filters, and photovoltaic (PV) cells. One approach to achieving a high voltage/low current configuration is to fabricate a device, where small area PV cells are monolithically series connected. The authors have termed this device a monolithic interconnected module (MIM). A MIM device has other advantages over conventional one-junction cells, such as simplified array interconnections and heat-sinking, and radiation recycling capability via a back surface reflector (BSR). The authors confine the contents of this article to the MIM materials, process development, and some optical results. The successful fabrication of InGaAs/InP MIM devices entails the development and optimization of several key components and processes. These include: isolation trench via geometry, selective chemical etching, contact and interconnect metallization, dielectric isolation barrier, back surface reflector (BSR), and anti-reflection (AR) coating. The selection, development, and testing of the materials and processes described above for MIM fabrication will be described.
Date: June 1, 1997
Creator: Fatemi, N.S.; Jenkins, P.P.; Hoffman, R.W. Jr.; Weizer, V.G.; Wilt, D.M.; Murray, C.S. et al.
Partner: UNT Libraries Government Documents Department

Measurement techniques for single junction thermophotovoltaic cells

Description: Several measurement systems and techniques for the electrical and thermal characterization of thermophotovoltaic (TPV) cells are discussed. One computer controlled system measures the quantum efficiency of cells from 0.8 to 2.6 microns. A probe resistor is used to account for cells with low shunt resistances. In the second system, a production-style robot provides automated measurements of I-V characteristics under dark, blackbody, and flashed illumination conditions. The system measures the length and width of each cell, and calculates the open circuit voltage, short circuit current, fill factor, and maximum power for each cell. The mean and standard deviation of the measured parameters are also computed. The third system measures the overall cell efficiency by a calorimetric technique. Heat losses due to radiation, conduction, and convection are factored into the analysis method.
Date: October 1, 1998
Creator: Danielson, L.R.; Parrington, J.R.; Charache, G.W.; Nichols, G.J. & Depoy, D.M.
Partner: UNT Libraries Government Documents Department

Lessons learned on closed cavity thermophotovoltaic system efficiency measurements

Description: Previous efficiency measurements have highlighted that to accurately measure and predict thermophotovoltaic (TPV) integrated cell or array efficiencies, a thorough understanding of the system is required. This includes knowledge of intrinsic diode and filter characteristics, radiative surface properties of all materials used within the cavity, and an intimate knowledge of the radiator/photon source. As a result of these and other lessons learned, the cavity test fixture used in earlier experiments was redesigned. To reduce radiator temperature gradients, the radiator was oversized and thickened, cavity walls were eliminated, the diode heat sink and shielding material were separated, and the cold side was redesigned to incorporate a steady state heat absorbed measurement technique. This redesigned test fixture provides an isothermal radiator and significantly enhances calorimetry capabilities. This newly designed cavity test fixture, in conjunction with the Monte Carlo Photon Transport code RACER-X, was used to improve and demonstrate the understanding of in-cavity TPV diode/module system efficiency testing. A single TPV diode was tested in this new fixture and yielded good agreement between measurements and predictions.
Date: October 1, 1998
Creator: Gethers, C.K.; Ballinger, C.T. & DePoy, D.M.
Partner: UNT Libraries Government Documents Department

Combustor design tool for a gas fired thermophotovoltaic energy converter

Description: Recently, there has been a renewed interest in thermophotovoltaic (TPV) energy conversion. A TPV device converts radiant energy from a high temperature incandescent emitter directly into electricity by photovoltaic cells. The current Department of Energy sponsored research involves the design, construction and demonstration of a prototype TPV converter that uses a hydrocarbon fuel (such as natural gas) as the energy source. As the photovoltaic cells are designed to efficiently convert radiant energy at a prescribed wavelength, it is important that the temperature of the emitter be nearly constant over its entire surface. The US Naval Academy has been tasked with the development of a small emitter (with a high emissivity) that can be maintained at 1,756 K (2,700 F). This paper describes the computer spreadsheet model that was developed as a tool to be used for the design of the high temperature emitter.
Date: July 1, 1995
Creator: Lindler, K.W. & Harper, M.J.
Partner: UNT Libraries Government Documents Department

Combustion powered thermophotovoltaic emitter system

Description: The US Naval Academy (USNA) has recently completed an engineering design project for a high temperature thermophotovoltaic (TPV) photon emitter. The final apparatus was to be portable, completely self contained, and was to incorporate cycle efficiency optimization such as exhaust stream recuperation. Through computer modeling and prototype experimentation, a methane fueled emitter system was designed from structural ceramic materials to fulfill the high temperature requirements necessary for high system efficiency. This paper outlines the engineering design process, discusses obstacles and solutions encountered, and presents the final design.
Date: July 1, 1995
Creator: McHenry, R.S.
Partner: UNT Libraries Government Documents Department

Thermovoltaic in-situ mirror cell

Description: A photovoltaic cell used in a direct energy conversion generator for converting heat to electricity includes a reflective layer disposed within the cell between the active layers of the cell and the cell substrate. The reflective layer reflects photons of low energy back to a photon producing emitter for reabsorption by the emitter, or reflects photons with energy greater than the cell bandgap back to the cell active layers for conversion into electricity. The reflective layer can comprise a reflective metal such as gold while the substrate can comprise a heavily doped silicon or a metal.
Date: December 31, 1995
Creator: Campbell, B.C.
Partner: UNT Libraries Government Documents Department

High-Performance, 0.6-eV, GA0.32In0.68As/In0.32P0.68 Thermophotovoltaic Converters and Monolithically Interconnected Modules

Description: Recent progress in the development of high-performance, 0.6-eV Ga0.32In0.68As/InAs0.32P0.68 thermophotovoltaic (TPV) converters and monolithically interconnected modules (MIMs) is described. The converter structure design is based on using a lattice-matched InAs0.32P0.68/Ga0.32In0.68As/InAs0.32P0.68 double-heterostructure (DH) device, which is grown lattice-mismatched on an InP substrate, with an intervening compositionally step-graded region of InAsyP1-y. The Ga0.32In0.68As alloy has a room-temperature band gap of {approx}0.6 eV and contains a p/n junction. The InAs0.32P0.68 layers have a room-temperature band gap of {approx}0.96 eV and serve as passivation/confinement layers for the Ga0.32In0.68As p/n junction. InAsyP1-y step grades have yielded DH converters with superior electronic quality and performance characteristics. Details of the microstructure of the converters are presented. Converters prepared for this work were grown by atmospheric-pressure metalorganic vapor-phase epitaxy (APMO VPE) and were processed using a combination of photolithography, wet-chemical etching, and conventional metal and insulator deposition techniques. Excellent performance characteristics have been demonstrated for the 0.6-eV TPV converters. Additionally, the implementation of MIM technology in these converters has been highly successful.
Date: December 15, 1998
Creator: Wanlass, M. W.; Carapella, J. J.; Duda, A.; Emery, K.; Gedvilas, L.; Moriarty, T. et al.
Partner: UNT Libraries Government Documents Department

Thermophotovoltaic Cells on Zinc Diffused Polycrystalline GaSb

Description: For the first time, it has been demonstrated that thermophotovoltaic cells made of polycrystalline GaSb with small grain sizes (down to 100 x 100 {micro}m) have similar characteristics to the best Zinc diffused single crystal GaSb cells with identified device parameters. The grain boundaries in polycrystalline GaSb do not degrade TPV cell parameters, indicating that such material can be used for high-efficiency thermophotovoltaic cells.
Date: May 1, 2000
Creator: Sulima, O.V.; Bett, A.W.; Dutta, P.S.; Ehsani, H. & Gutmann, R.J.
Partner: UNT Libraries Government Documents Department

A thermovoltaic semiconductor device including a plasma filter

Description: A thermovoltaic energy conversion device and related method for converting thermal energy into an electrical potential are disclosed. An interference filter is provided on a semiconductor thermovoltaic cell to pre-filter black body radiation. The semiconductor thermovoltaic cell includes a P/N junction supported on a substrate which converts incident thermal energy below the semiconductor junction band gap into electrical potential. The semiconductor substrate is doped to provide a plasma filter which reflects back energy having a wavelength which is above the band gap and which is ineffectively filtered by the interference filter, through the P/N junction to the source of radiation thereby avoiding parasitic absorption of the unusable portion of the thermal radiation energy.
Date: December 1, 1997
Creator: Baldasaro, Paul F.
Partner: UNT Libraries Government Documents Department