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The Multilayer Insulation (MLI) Blanket
Published in Juan Cepeda-Rizo, Jeremiah Gayle, Joshua Ravich, Thermal and Structural Electronic Packaging Analysis for Space and Extreme Environments, 2021
Juan Cepeda-Rizo, Jeremiah Gayle, Joshua Ravich
Bakeout. Bakeout reduces the risk of contamination prior to testing in a vacuum as well as lowers the risk of hardware contamination. Blanket materials tend to harbor water vapor, especially from the Dacron scrim. Typical bakeout duration may vary according to temperature, and the material provider should be consulted.
Controlling Indoor Air Problems: How to Keep the Building Working Well
Published in H.E. Burroughs, Shirley J. Hansen, Managing Indoor Air Quality, 2020
H.E. Burroughs, Shirley J. Hansen
Bake-outs were frequently suggested early-on as part of the commissioning process to control VOC contaminants in new construction. Elevated temperatures were thought to speed VOC emissions. The bakeout was, therefore, expected to accelerate the off-gassing process prior to occupancy and thus reduce the pollution levels after the building is occupied. A bake-out was controlled by adjusting three parameters; the duration of the bake-out, the indoor air temperature during the bakeout, and the ventilation rate during the process. In 1989, J. Girman and his colleagues reported reduction of selected VOCs as a result of the bake-out process. He also confided in verbal reporting that the research building suffered substantial physical damage to wall coverings, concrete foundation, and millwork. Researchers, headed by C. Bayer, at the Georgia Institute of Technology, later reported that total counts of VOCs were “about the same before and after the bake-out,” but they found that numerous specific compounds had shifted to other totally new organic compounds. Bayer theorized that the higher levels of VOCs had transported to sorption sites and from these “sinks” re-emitted sometimes as new compounds. The bake-out process must be performed after the building is totally furnished and ready for occupancy. Yet, there must be no occupancy during the process. This creates tremendous financial burden to the owner who must delay the useful start time of the asset.
Extreme High Vacuum
Published in Pramod K. Naik, Vacuum, 2018
A high-temperature (up to 450°C) bake of the vacuum system can be used by employing an oven that can supply heat with uniform temperature distribution. It has been discussed previously in Section 3.1.4 why high-temperature bakeout is essential to minimize the outgassing rates from the walls of the system exposed to vacuum. The maximum bakeout temperature is limited by the materials used in the system. Bakeout at 450°C for a few hours is adequate to significantly reduce the outgassing rates from the walls of all-metal systems with glass gauge-heads. Bakeout temperatures of higher than 450°C could be harmful for borosilicate glass generally used for gauge-heads. Uniform heating of the system has to be ensured to avoid temperature gradients. In metal and glass systems, mostly water vapour, CO and H2 are released during the bakeout. Outgassing rates after bakeout can be estimated upon isolating the pump from the rest of the system and then by measuring the rate of rise of pressure in the system of known volume and surface area. Hobson21 obtained outgassing rate of 2.5 × 10 –13 Pa·m·s –1 for alumina silicate glass after baking at 500°C for 18 hours, followed by 600°C for 2 hours, 700°C for 2 hours and 500°C for 10 hours.
MEPhIST-0 Tokamak for Education and Research
Published in Fusion Science and Technology, 2023
S. Krat, A. Prishvitsyn, A. Alieva, N. Efimov, E. Vinitskiy, D. Ulasevich, A. Izarova, F. Podolyako, A. Belov, A. Meshcheryakov, J. Ongena, N. Kharchev, A. Chernenko, R. Khayrutdinov, V. Lukash, D. Sinelnikov, D. Bulgadaryan, I. Sorokin, K. Gubskiy, A. Kaziev, D. Kolodko, V. Tumarkin, A. Isakova, A. Grunin, L. Begrambekov, R. Voskoboinikov, A. Melnikov
The vacuum is achieved by two Leybold Turbovac 350i turbomolecular pumps, with the total effective pumping rate of 200 L/s. The ultimate pressure is ~3 × 10−7 mbar, achieved after around 1 day of pumping. Currently, no chamber heating technique has been implemented, however glow discharge can be used for wall conditioning. To make it possible to bake out the vacuum vessel in the future, the vessel is anchored to a supporting frame by three points located in the midplane of the tokamak. The anchoring points can freely move in the radial direction. This means that when the vessel expands due to baking, the anchoring to the support frame won’t apply additional stresses to the vessel.
Hydride Bed Helium-3 Recovery and Partial Regeneration
Published in Fusion Science and Technology, 2021
P. J. Foster, Z. J. Trotter, S. A. Schaufler, J. L. Clark, G. C. Staack, J. E. Klein
The amount of 3He in the desorbed gas is another way to monitor the long-term impact of the bake-out. Prior to the bake-out, the desorption temperature was reduced to prevent 3He release from the material. Following the bake-out, the bed was heated to normal desorption temperatures, and the amount of 3He release has been well within the required thresholds. It is expected that the significant improvement in performance will decrease over time as the bed continues to be exposed to tritium and 3He accumulates in the material. However, additional bake-outs could potentially restore bed performance.
The evolution of He+ irradiation-induced point defects and helium retention in nuclear graphite
Published in Journal of Nuclear Science and Technology, 2019
Mingyang Li, Chuanqing Shi, Henk Schut, Zhengjun Zhang, Zhengcao Li
The TDS technique has been used to monitor the release of helium gas atoms from the implanted samples during ramp heating. The TDS measurement was performed on the DEGA desorption setup at Delft University of Technology. In order to reduce the background contribution caused by the adsorbed gas on the specimens and vacuum chamber walls, an overnight bake-out at a temperature of approximately 400 K was performed. During the TDS measurement, the samples were heated up to 1200 K at a constant ramping rate of 0.5 K s−1, and the release of He was monitored using a Pfeiffer Quadrupole Mass spectrometer.