The Experts below are selected from a list of 90 Experts worldwide ranked by ideXlab platform
Julia Himmelsbach - One of the best experts on this subject based on the ideXlab platform.
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Influence of High Rotational Speeds on Heat Transfer and Oil Film Thickness in Aero-Engine Bearing Chambers
Journal of Engineering for Gas Turbines and Power, 1994Co-Authors: Sigmar Wittig, Alexander Glahn, Julia HimmelsbachAbstract:Increasing the thermal loading of bearing chambers in modern aero-engines requires advanced techniques for the determination of heat transfer characteristics. In the present study, film thickness and heat transfer measurements have been carried out for the complex two-phase oil/air flow in bearing chambers. In order to ensure real engine conditions, a new test facility has been built up, designed for rotational speeds up to n = 16,000 rpm and maximum flow Temperatures of Tmax = 473 K. Sealing air and lubrication oil flow can be varied nearly in the whole range of aero-engine applications. Special interest is directed toward the development of an ultrasonic oil film thickness measuring technique, which can be used without any reaction on the flow inside the chamber. The determination of local heat transfer at the bearing chamber housing is based on a well-known Temperature Gradient Method using surface Temperature measurements and a finite element code to determine Temperature distributions within the bearing chamber housing. The influence of high rotational speed on the local heat transfer and the oil film thickness is discussed.
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influence of high rotational speeds on heat transfer and oil film thickness in aero engine bearing chambers
ASME 1993 International Gas Turbine and Aeroengine Congress and Exposition, 1993Co-Authors: Sigmar Wittig, Axel Glahn, Julia HimmelsbachAbstract:Increasing the thermal loading of bearing chambers in modern aero engines requires advanced techniques for the determination of heat transfer characteristics. In the present study, film thickness and heat transfer measurements have been carried out for the complex two–phase oil/air flow in bearing chambers. In order to ensure real engine conditions, a new test facility has been built up, designed for rotational speeds up to n = 16000 rpm and maximum flow Temperatures of Tmax = 473K. Sealing air and lubrication oil flow can be varied nearly in the whole range of aero engine applications. Special interest is directed towards the development of an ultrasonic oil film thickness measuring technique which can be used without any reaction on the flow inside the chamber. The determination of local heat transfer at the bearing chamber housing is based on a well known Temperature Gradient Method using surface Temperature measurements and a finite element code to determine Temperature distributions within the bearing chamber housing. The influence of high rotational speed on the local heat transfer and the oil film thickness is discussed.Copyright © 1993 by ASME
Shuichi Satoh - One of the best experts on this subject based on the ideXlab platform.
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growth rate of high quality large diamond crystals
Journal of Crystal Growth, 2002Co-Authors: Hitoshi Sumiya, Naohiro Toda, Shuichi SatohAbstract:Abstract In the diamond growth by Temperature Gradient Method under high pressure and high Temperature, the growth of a high-quality diamond crystal without metal inclusions has been investigated. Large high-quality type IIa diamond crystals without impurities of 7–8 ct (about 10 mm across) can be grown at a high growth rate of 6–7 mg/h by prolonged maintenance of a high-precision Temperature control with an adequate selection of solvent metal and additives. Type Ib diamond crystals containing nitrogen impurities can be grown at higher growth rates up to 15 mg/h by using large seed crystals and adjusting the morphology with Temperature control. This large seed Method is not applicable for growing a type IIa diamond crystal because it is hard to control the crystal morphology of it.
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crystalline perfection of high purity synthetic diamond crystal
Journal of Crystal Growth, 1997Co-Authors: Hitoshi Sumiya, Naohiro Toda, Yoshiki Nishibayashi, Shuichi SatohAbstract:Crystalline quality of high purity synthetic diamond crystals (type IIa) with impurities less than 0.1 ppm grown by a Temperature Gradient Method under high-pressure and high-Temperature has been investigated in detail. The crystal defects and internal strains of the synthetic type IIa diamonds were studied by double-crystal X-ray rocking curve measurement, polarizing microscopy, X-ray topography and Raman spectroscopy. The synthetic type IIa diamonds were found to have high crystalline quality with fewer crystal defects, less internal strain and less variation in defects among crystals than those of natural diamonds or synthetic type Ib diamonds. However, in the synthetic type IIa diamond crystal some line and plane defects were observed. It was found that by using strain-free and low defect crystals for the seeds, the line defects (dislocation bundles) could be removed, thereby improving the crystalline quality of the synthetic type IIa diamonds.
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high pressure synthesis of high purity diamond crystal
Diamond and Related Materials, 1996Co-Authors: Hitoshi Sumiya, Shuichi SatohAbstract:High-purity type IIa diamond crystals of weight 1–2 carats, containing less than 0.1 ppm chemical impurities and few inclusions, have been successfully synthesized by a Temperature Gradient Method at high pressures and Temperatures. The concentration of nitrogen impurities in the diamond crystals was reduced to less than 0.1 ppm by adding an element of the IVa group to the solvent as a nitrogen getter. The boron impurity concentration was reduced to less than 0.1 ppm by using a high-purity graphite (<1 ppm impurities) as the carbon source. Nickel impurities were avoided by using an Fe-Co alloy system for the solvent. Furthermore, by adding elements which can reduce the formation of carbides such as TiC or ZrC in the solvent, inclusions of the carbide or the solvent metal in the diamond crystal were substantially decreased, and consequently good-quality type IIa diamond crystals were obtained even at a growth rate as high as 2–3 mg h−1.
Sigmar Wittig - One of the best experts on this subject based on the ideXlab platform.
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Influence of High Rotational Speeds on Heat Transfer and Oil Film Thickness in Aero-Engine Bearing Chambers
Journal of Engineering for Gas Turbines and Power, 1994Co-Authors: Sigmar Wittig, Alexander Glahn, Julia HimmelsbachAbstract:Increasing the thermal loading of bearing chambers in modern aero-engines requires advanced techniques for the determination of heat transfer characteristics. In the present study, film thickness and heat transfer measurements have been carried out for the complex two-phase oil/air flow in bearing chambers. In order to ensure real engine conditions, a new test facility has been built up, designed for rotational speeds up to n = 16,000 rpm and maximum flow Temperatures of Tmax = 473 K. Sealing air and lubrication oil flow can be varied nearly in the whole range of aero-engine applications. Special interest is directed toward the development of an ultrasonic oil film thickness measuring technique, which can be used without any reaction on the flow inside the chamber. The determination of local heat transfer at the bearing chamber housing is based on a well-known Temperature Gradient Method using surface Temperature measurements and a finite element code to determine Temperature distributions within the bearing chamber housing. The influence of high rotational speed on the local heat transfer and the oil film thickness is discussed.
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influence of high rotational speeds on heat transfer and oil film thickness in aero engine bearing chambers
ASME 1993 International Gas Turbine and Aeroengine Congress and Exposition, 1993Co-Authors: Sigmar Wittig, Axel Glahn, Julia HimmelsbachAbstract:Increasing the thermal loading of bearing chambers in modern aero engines requires advanced techniques for the determination of heat transfer characteristics. In the present study, film thickness and heat transfer measurements have been carried out for the complex two–phase oil/air flow in bearing chambers. In order to ensure real engine conditions, a new test facility has been built up, designed for rotational speeds up to n = 16000 rpm and maximum flow Temperatures of Tmax = 473K. Sealing air and lubrication oil flow can be varied nearly in the whole range of aero engine applications. Special interest is directed towards the development of an ultrasonic oil film thickness measuring technique which can be used without any reaction on the flow inside the chamber. The determination of local heat transfer at the bearing chamber housing is based on a well known Temperature Gradient Method using surface Temperature measurements and a finite element code to determine Temperature distributions within the bearing chamber housing. The influence of high rotational speed on the local heat transfer and the oil film thickness is discussed.Copyright © 1993 by ASME
V D Blank - One of the best experts on this subject based on the ideXlab platform.
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electrical properties of the high quality boron doped synthetic single crystal diamonds grown by the Temperature Gradient Method
Diamond and Related Materials, 2013Co-Authors: V S Bormashov, M S Kuznetsov, S A Terentiev, S A Tarelkin, S G Buga, A N Semenov, V D BlankAbstract:Abstract Temperature dependencies of the resistivity and the Hall coefficient in high-quality boron-doped synthetic single crystal diamonds grown by the high-pressure-high-Temperature (HPHT) Method with different boron contents have been investigated. The concentration of acceptors was varied in the range of 2 × 1015 to 3 × 1017 cm–3 in (001) cut plates by a change of boron content in a growth mixture in a range from 0.0004 to 0.04 atomic percent. A special sample preparation has been used for precise measurements. Thin rectangular plates with uniform boron content and without linear and planar structure defects have been laser cut after X-ray topography and UV-luminescence mapping. The donor and acceptor concentrations in each sample have been calculated from the Hall effect data and capacitance–voltage characteristics. The concentrations correlate with the boron content in a growth mixture. Minimum donor to acceptor compensation ratio slightly below 1% was observed at 0.002 at.% boron content in a growth mixture, while it increased at an increase and decrease of boron amount. Samples grown at such boron concentration had maximum carrier mobility. It was 2200 cm2 / (V × s) at T = 300 K and 7200 cm2 / (V × s) at T = 180 K. The phonon scattering of holes dominates in the entire Temperature range of 180–800 K, while the scattering by point defects such as neutral and ionized impurity atoms is insignificant. Due to a perfect crystal quality and lattice scattering mechanism bulk diamond crystals grown from the mixture containing 0.0005 to 0.002 at.% of boron may serve as reference semiconductor materials.
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the influence of crystallization Temperature and boron concentration in growth environment on its distribution in growth sectors of type iib diamond
Diamond and Related Materials, 2007Co-Authors: V D Blank, M S Kuznetsov, S A Nosukhin, S A Terentiev, V N DenisovAbstract:Abstract Type IIb diamond single crystals of size up to 8 mm were grown using the Temperature-Gradient Method at high static pressure and Temperature in Fe–Al–C system with added boron. The influence of crystallization Temperature and boron concentration in growth environment on its distribution in growth sectors has been investigated using optical techniques. Variation from cubo-octahedral to octahedral habit with an increasing added amount of boron has been noted and explained.
Hitoshi Sumiya - One of the best experts on this subject based on the ideXlab platform.
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large defect free synthetic type iia diamond crystals synthesized via high pressure and high Temperature
Japanese Journal of Applied Physics, 2012Co-Authors: Hitoshi Sumiya, Kenji TamasakuAbstract:Large high-quality type IIa diamond crystals measuring up to 12 mm in diameter were successfully synthesized by the Temperature Gradient Method at high pressure and high Temperature, using high-crystalline-quality (001)-oriented seed crystals, and by controlling the Temperature conditions with high precision. The X-ray projection topograph using a synchrotron radiation beam revealed that the large synthetic diamond crystals are characterized by high-crystalline-quality, having no dislocation or stacking fault in the (001) growth sectors in the upper part of the crystals grown on seeds. Diamond crystals containing a large defect free area of 5 ×5 mm2 or more were successfully produced by controlling the Temperature strictly on the low-Temperature side in the synthesis region for growing type IIa diamond crystals to allow the (001) growth sectors to become dominant.
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growth rate of high quality large diamond crystals
Journal of Crystal Growth, 2002Co-Authors: Hitoshi Sumiya, Naohiro Toda, Shuichi SatohAbstract:Abstract In the diamond growth by Temperature Gradient Method under high pressure and high Temperature, the growth of a high-quality diamond crystal without metal inclusions has been investigated. Large high-quality type IIa diamond crystals without impurities of 7–8 ct (about 10 mm across) can be grown at a high growth rate of 6–7 mg/h by prolonged maintenance of a high-precision Temperature control with an adequate selection of solvent metal and additives. Type Ib diamond crystals containing nitrogen impurities can be grown at higher growth rates up to 15 mg/h by using large seed crystals and adjusting the morphology with Temperature control. This large seed Method is not applicable for growing a type IIa diamond crystal because it is hard to control the crystal morphology of it.
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crystalline perfection of high purity synthetic diamond crystal
Journal of Crystal Growth, 1997Co-Authors: Hitoshi Sumiya, Naohiro Toda, Yoshiki Nishibayashi, Shuichi SatohAbstract:Crystalline quality of high purity synthetic diamond crystals (type IIa) with impurities less than 0.1 ppm grown by a Temperature Gradient Method under high-pressure and high-Temperature has been investigated in detail. The crystal defects and internal strains of the synthetic type IIa diamonds were studied by double-crystal X-ray rocking curve measurement, polarizing microscopy, X-ray topography and Raman spectroscopy. The synthetic type IIa diamonds were found to have high crystalline quality with fewer crystal defects, less internal strain and less variation in defects among crystals than those of natural diamonds or synthetic type Ib diamonds. However, in the synthetic type IIa diamond crystal some line and plane defects were observed. It was found that by using strain-free and low defect crystals for the seeds, the line defects (dislocation bundles) could be removed, thereby improving the crystalline quality of the synthetic type IIa diamonds.
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high pressure synthesis of high purity diamond crystal
Diamond and Related Materials, 1996Co-Authors: Hitoshi Sumiya, Shuichi SatohAbstract:High-purity type IIa diamond crystals of weight 1–2 carats, containing less than 0.1 ppm chemical impurities and few inclusions, have been successfully synthesized by a Temperature Gradient Method at high pressures and Temperatures. The concentration of nitrogen impurities in the diamond crystals was reduced to less than 0.1 ppm by adding an element of the IVa group to the solvent as a nitrogen getter. The boron impurity concentration was reduced to less than 0.1 ppm by using a high-purity graphite (<1 ppm impurities) as the carbon source. Nickel impurities were avoided by using an Fe-Co alloy system for the solvent. Furthermore, by adding elements which can reduce the formation of carbides such as TiC or ZrC in the solvent, inclusions of the carbide or the solvent metal in the diamond crystal were substantially decreased, and consequently good-quality type IIa diamond crystals were obtained even at a growth rate as high as 2–3 mg h−1.
