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W. Zawadzki - One of the best experts on this subject based on the ideXlab platform.
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Magnetic thaw down and Boil-off of electrons in the quantum Hall effect regime due to magnetoacceptors in GaAs/GaAlAs heterostructures
Physical Review B : Condensed matter and materials physics, 2012Co-Authors: I. Bisotto, Christophe Chaubet, Andre Raymond, Jc Harmand, M. Kubisa, W. ZawadzkiAbstract:The quantum Hall effect (QHE) and the Shubnikov-de Haas effect in the QHE regime are investigated experimentally using modulation doped n-type GaAs/GaAlAs quantum wells additionally doped in the well with beryllium. It is known that acceptor states introduced by Be atoms have a localized character in the conduction band due to a combined effect of the well and a magnetic field parallel to the growth direction and that they possess discrete energies above the corresponding conduction Landau levels. It is presently shown that the localized magnetoacceptor (MA) states lead to two observable effects in magnetotransport in the ultraquantum limit: magnetic thaw down and magnetic Boil-off of two-dimensional (2D) electrons. Both effects are related to the fact that electrons occupying localized MA states cannot conduct. Thus in the thaw down effect the electrons fall down from the MA states to the free Landau states, which leads to a shift of the Hall plateau toward higher magnetic fields as a consequence of an increase of the 2D electron density Ns. In the Boil-off effect the electrons are pushed from the free Landau states to the MA states which leads to a dramatic increase of resistance, as a consequence of the decrease of Ns. Differences between the above effects and those induced by magnetodonors in 2D systems are emphasized. We analyze the magnetic Boil-off effect theoretically assuming that it is caused by the quantum Hall electric field present in our experiments. It is demonstrated that a sufficiently strong electric field in the crossed-field configuration can indeed populate localized MA states above the Landau levels.
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Magnetic thaw down and Boil-off of electrons in the quantum Hall effect regime due to magnetoacceptors in GaAs/GaAlAs heterostructures
Physical Review B, 2012Co-Authors: I. Bisotto, Christophe Chaubet, Andre Raymond, Jc Harmand, M. Kubisa, W. ZawadzkiAbstract:International audienceThe quantum Hall effect (QHE) and the Shubnikov-de Haas effect in the QHE regime are investigated experimentally using modulation doped n-type GaAs/GaAlAs quantum wells additionally doped in the well with beryllium. It is known that acceptor states introduced by Be atoms have a localized character in the conduction band due to a combined effect of the well and a magnetic field parallel to the growth direction and that they possess discrete energies above the corresponding conduction Landau levels. It is presently shown that the localized magnetoacceptor (MA) states lead to two observable effects in magnetotransport in the ultraquantum limit: magnetic thaw down and magnetic Boil-off of two-dimensional (2D) electrons. Both effects are related to the fact that electrons occupying localized MA states cannot conduct. Thus in the thaw down effect the electrons fall down from the MA states to the free Landau states, which leads to a shift of the Hall plateau toward higher magnetic fields as a consequence of an increase of the 2D electron density Ns. In the Boil-off effect the electrons are pushed from the free Landau states to the MA states which leads to a dramatic increase of resistance, as a consequence of the decrease of Ns. Differences between the above effects and those induced by magnetodonors in 2D systems are emphasized. We analyze the magnetic Boil-off effect theoretically assuming that it is caused by the quantum Hall electric field present in our experiments. It is demonstrated that a sufficiently strong electric field in the crossed-field configuration can indeed populate localized MA states above the Landau levels
M. Babaelahi - One of the best experts on this subject based on the ideXlab platform.
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thermoeconomic optimization of a cryogenic refrigeration cycle for re liquefaction of the lng boil off gas
International Journal of Refrigeration-revue Internationale Du Froid, 2010Co-Authors: Hoseyn Sayyaadi, M. BabaelahiAbstract:The development of the liquefaction process for the Liquefied Natural Gas (LNG) Boil-off re-liquefaction plants will be addressed to provide an environmentally friendly and cost effective solution for the gas transportation. In this manner, onboard Boil-off gas (BOG) re-liquefaction system as a cryogenic refrigeration cycle is utilized in order to re-liquefy the BOG and returns it to the cargo tanks instead of burning it. In this paper, a thermoeconomic optimization of the LNG-BOG liquefaction system is performed. A thermoeconomic model based on energy and exergy analyses and an economic model according to the total revenue requirement (TRR) are developed. Minimizing of the unit cost of the refrigeration effect as a product of BOG re-liquefaction plant is performed using the genetic algorithm. Results of thermoeconomic optimization are compared with corresponding features of the base case system. Finally, sensitivity of the total cost of the system product with respect to the variation of some operating parameters is studied.
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Exergetic Optimization of a Refrigeration Cycle for Re-Liquefaction of LNG Boil-off Gas
International Journal of Thermodynamics, 2010Co-Authors: Hoseyn Sayyaadi, M. BabaelahiAbstract:The development of a liquefaction process for liquefied natural gas Boil-off re-liquefaction plants will be addressed to provide an environmentally friendly and cost effective solution for gas transport. Onboard Boil-off gas (BOG) reliquefaction is a new technology that liquefies BOG and returns it to the cargo tanks instead of burning it. Exergetic efficiency optimization for a cryogenic refrigeration cycle for re-liquefaction of LNG Boil-off gas is performed. Thermodynamic modeling has been performed based on energy and exergy analyses. Objective problem is developed based on maximization of the plant exergetic efficiency and selected decision variables and constraints. Optimization process is performed using MATLAB genetic algorithm optimization toolbox. The results of exergetic efficiency optimization are compared with the corresponding results of the base case system obtained in the previous study. Finally, effects of some operating parameters on the exergetic efficiency are discussed by sensitivity analysis.
Yves Bréchet - One of the best experts on this subject based on the ideXlab platform.
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Ablative degradation of cryogenic thermal protection and fuel Boil-off: Improvement of using graded density insulators
International Journal of Heat and Mass Transfer, 2011Co-Authors: Jaona Randrianalisoa, Rémy Dendievel, Yves BréchetAbstract:A simple modeling of the heat transfer through insulating bilayers of cryogenic reservoir subjected to surrounding environment or aerothermal flux is presented. The model permits to determine the instantaneous evolution of maximum fuel temperatures and the Boil-off rate as well as the possible insulation ablation. To get a realistic estimation of the maximum fuel temperature and Boil-off loss, the good knowledge of the internal convection coefficient, taking into account the possible fuel ebullition, is indispensable. The aerothermal flux provokes the insulation degradation and its ablation. Because of the ablation, the reservoir becomes less and less thermally protected, which may cause an important fuel Boil-off. Compared to classical insulations with uniform density, those with spatially graded densities appear as potential insulations permitting to meet both light-weight and low Boil-off requirements.
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Ablative degradation of cryogenic thermal protection and fuel Boil-off: Improvement of using graded density insulators
International Journal of Heat and Mass Transfer, 2011Co-Authors: Jaona Randrianalisoa, Rémy Dendievel, Yves BréchetAbstract:A simple modeling of the heat transfer through insulating bilayers of cryogenic reservoir subjected to surrounding environment or aerothermal flux is presented. The model permits to determine the instantaneous evolution of maximum fuel temperatures and the Boil-off rate as well as the possible insulation ablation. To get a realistic estimation of the maximum fuel temperature and Boil-off loss, the good knowledge of the internal convection coefficient, taking into account the possible fuel ebullition, is indispensable. The aerothermal flux provokes the insulation degradation and its ablation. Because of the ablation, the reservoir becomes less and less thermally protected, which may cause an important fuel Boil-off. Compared to classical insulations with uniform density, those with spatially graded densities appear as potential insulations permitting to meet both light-weight and low Boil-off requirements. (C) 2011 Elsevier Ltd. All rights reserved.
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Ablative degradation of cryogenic thermal protection and fuel Boil-off: Improvement of using graded density insulators
International Journal of Heat and Mass Transfer, 2011Co-Authors: Jaona Randrianalisoa, Rémy Dendievel, Yves BréchetAbstract:International audienceA simple modeling of the heat transfer through insulating bilayers of cryogenic reservoir subjected to surrounding environment or aerothermal flux is presented. The model permits to determine the instantaneous evolution of maximum fuel temperatures and the Boil-off rate as well as the possible insulation ablation. To get a realistic estimation of the maximum fuel temperature and Boil-off loss, the good knowledge of the internal convection coefficient, taking into account the possible fuel ebullition, is indispensable. The aerothermal flux provokes the insulation degradation and its ablation. Because of the ablation, the reservoir becomes less and less thermally protected, which may cause an important fuel Boil-off. Compared to classical insulations with uniform density, those with spatially graded densities appear as potential insulations permitting to meet both light-weight and low Boil-off requirements. (C) 2011 Elsevier Ltd. All rights reserved
H Simgen - One of the best experts on this subject based on the ideXlab platform.
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radon depletion in xenon boil off gas
European Physical Journal C, 2017Co-Authors: S Bruenner, Sabine Lindemann, Marrodan T Undagoitia, D. Cichon, H SimgenAbstract:An important background in detectors using liquid xenon for rare event searches arises from the decays of radon and its daughters. We report for the first time a reduction of \(^{222}\)Rn in the gas phase above a liquid xenon reservoir. We show a reduction factor of \(\gtrsim 4\) for the \(^{222}\)Rn concentration in Boil-off xenon gas compared to the radon enriched liquid phase. A semiconductor-based \(\alpha \)-detector and miniaturized proportional counters are used to detect the radon. As the radon depletion in the Boil-off gas is understood as a single-stage distillation process, this result establishes the suitability of cryogenic distillation to separate radon from xenon down to the \(10^{-15}\) mol/mol level.
D W Plachta - One of the best experts on this subject based on the ideXlab platform.
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NASA Cryocooler Technology Developments and Goals to Achieve Zero Boil-off and to Liquefy Cryogenic Propellants for Space Exploration
Cryogenics, 2018Co-Authors: D W Plachta, Jonathan R. Stephens, Wesley L. Johnson, M. ZagarolaAbstract:Abstract NASA’s interest in human exploration of Mars has driven it to invest in 20 K cryocooler technology to achieve zero Boil-off of liquid hydrogen and 90 K cryocooler technology to achieve zero Boil-off liquid oxygen or liquid methane as well as to liquefy oxygen or methane that is produced on the surface of Mars. These investments have demonstrated efficiency progress, mass reductions, and integration insights. A history of the application of cryocooler technology to zero Boil-off propellant storage is presented. A trade space on distributed cooling is shown, along with the progress of reverse turbo-Brayton cycle cryocoolers, where the specific power and specific mass have dropped, decreasing the mass and power of these cryocoolers. Additionally, the cryocooler technology advancements of recuperators and compressors are described. Finally, NASA’s development ideas with respect to zero Boil-off technology are discussed.
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Zero Boil-off system testing
Cryogenics, 2016Co-Authors: D W Plachta, W. L. Johnson, J R FellerAbstract:Cryogenic propellants such as liquid hydrogen (LH2) and liquid oxygen (LO2) are a part of NASA's future space exploration plans due to their high specific impulse for rocket motors of upper stages. However, the low storage temperatures of LH2 and LO2 cause substantial Boil-off losses for long duration missions. These losses can be eliminated by incorporating high performance cryocooler technology to intercept heat load to the propellant tanks and modulating the cryocooler temperature to control tank pressure. The technology being developed by NASA is the reverse turbo-Brayton cycle cryocooler and its integration to the propellant tank through a distributed cooling tubing network coupled to the tank wall. This configuration was recently tested at NASA Glenn Research Center in a vacuum chamber and cryoshroud that simulated the essential thermal aspects of low Earth orbit, its vacuum and temperature. This test series established that the active cooling system integrated with the propellant tank eliminated Boil-off and robustly controlled tank pressure.
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Reduced Boil-off System Sizing
2015Co-Authors: Monica C. Guzik, D W Plachta, J R FellerAbstract:NASA is currently developing cryogenic propellant storage and transfer systems for future space exploration and scientific discovery missions by addressing the need to raise the technology readiness level of cryogenic fluid management technologies. Cryogenic propellants are baselined in many propulsion systems due to their inherently high specific impulse; however, their low boiling points can cause substantial Boil-off losses over time. Recent efforts such as the Reduced Boil-off Testing and the Active Thermal Control Scaling Study provide important information on the benefit of an active cooling system applied to LH2 propellant storage. Findings show that zero-boil off technologies can reduce overall mass in LH2 storage systems when low Earth orbit loiter periods extend beyond two months. A significant part of this mass reduction is realized by integrating two stages of cooling: a 20 K stage to intercept heat at the tank surface, and a 90 K stage to reduce the heat entering the less efficient 20 K stage. A missing element in previous studies, which is addressed in this paper, is the development of a direct method for sizing the 90 K cooling stage. Such a method requires calculation of the heat entering both the 90 K and 20 K stages as compared to the overall system masses, and is reliant upon the temperature distribution, performance, and unique design characteristics of the system in question. By utilizing the known conductance of a system without active thermal control, the heat being intercepted by a 90 K stage can be calculated to find the resultant lift and mass of each active thermal control stage. Integral to this is the thermal conductance of the cooling straps and the broad area cooling shield, key parts of the 90 K stage. Additionally, a trade study is performed to show the ability of the 90 K cooling stage to reduce the lift on the 20 K cryocooler stage, which is considerably less developed and efficient than 90 K cryocoolers.
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design fabrication and test of load bearing multilayer insulation to support a broad area cooled shield
Cryogenics, 2014Co-Authors: Wesley L. Johnson, D W Plachta, G L Mills, L Buchanan, A B KopeloveAbstract:Abstract Improvements in cryogenic propellant storage are needed to achieve reduced or Zero Boil Off of cryopropellants, critical for long duration missions. Techniques for reducing heat leak into cryotanks include using passive multi-layer insulation (MLI) and vapor cooled or actively cooled thermal shields. Large scale shields cannot be supported by tank structural supports without heat leak through the supports. Traditional MLI also cannot support shield structural loads, and separate shield support mechanisms add significant heat leak. Quest Thermal Group and Ball Aerospace, with NASA SBIR support, have developed a novel Load Bearing multi-layer insulation (LBMLI) capable of self-supporting thermal shields and providing high thermal performance. We report on the development of LBMLI, including design, modeling and analysis, structural testing via vibe and acoustic loading, calorimeter thermal testing, and Reduced Boil-off (RBO) testing on NASA large scale cryotanks. LBMLI uses the strength of discrete polymer spacers to control interlayer spacing and support the external load of an actively cooled shield and external MLI. Structural testing at NASA Marshall was performed to beyond maximum launch profiles without failure. LBMLI coupons were thermally tested on calorimeters, with superior performance to traditional MLI on a per layer basis. Thermal and structural tests were performed with LBMLI supporting an actively cooled shield, and comparisons are made to the performance of traditional MLI and thermal shield supports. LBMLI provided a 51% reduction in heat leak per layer over a previously tested traditional MLI with tank standoffs, a 38% reduction in mass, and was advanced to TRL5. Active thermal control using LBMLI and a broad area cooled shield offers significant advantages in total system heat flux, mass and structural robustness for future Reduced Boil-off and Zero Boil-off cryogenic missions with durations over a few weeks.
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Cryogenic Boil-off Reduction System Testing
50th AIAA ASME SAE ASEE Joint Propulsion Conference, 2014Co-Authors: D W Plachta, Wesley L. Johnson, J R FellerAbstract:Cryogenic propellants such as liquid hydrogen (LH2) and liquid oxygen (LO2) are a part of NASA's future space exploration due to the high specific impulse that can be achieved using engines suitable for moving 10's to 100's of metric tons of payload mass to destinations outside of low earth orbit. However, the low storage temperatures of LH2 and LO2 cause substantial Boil-off losses for missions with durations greater than several days. The losses can be greatly reduced by incorporating high performance cryocooler technology to intercept heat load to the propellant tanks and by the integration of self-supporting multi-layer insulation. The active thermal control technology under development is the integration of the reverse turbo- Brayton cycle cryocooler to the propellant tank through a distributed cooling network of tubes coupled to a shield in the tank insulation and to the tank wall itself. Also, the self-supporting insulation technology was utilized under the shield to obtain needed tank applied LH2 performance. These elements were recently tested at NASA Glenn Research Center in a series of three tests, two that reduced LH2 Boil-off and one to eliminate LO2 Boil-off. This test series was conducted in a vacuum chamber that replicated the vacuum of space and the temperatures of low Earth orbit. The test results show that LH2 Boil-off was reduced 60% by the cryocooler system operating at 90K and that robust LO2 zero Boil-off storage, including full tank pressure control was achieved.