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971.
972.
重力辅助环路热管稳态运行特性的实验研究 总被引:4,自引:1,他引:4
随着环路热管应用领域不断扩展,其可能在各种姿态下运行,包括重力辅助姿态。对环路热管在重力辅助姿态下的稳态运行规律和特性进行了实验研究,并同平放及反重力条件下的运行特性进行了比较。通过实验可得出,在重力辅助姿态下,环路热管存在两种驱动模式,即重力单独驱动模式和毛细力与重力共同驱动模式。当热载荷较小时,环路热管工作在重力单独驱动模式,蒸汽管线内为气液两相工质,回流液体对储液器的冷却作用加强,运行温度明显低于平放及反重力条件下之值,热导显著增大;当热载荷大于某一临界值,环路热管工作在毛细力与重力共同驱动模式,蒸汽管线内为单相蒸汽,运行温度同平放及反重力条件下之值基本一致。最后,从环路热管系统压力平衡和储液器能量平衡的角度对上述实验现象进行了解释和分析。 相似文献
973.
采用置换原子的热力学模型,计算了Ni-Al-Ta/Mo合金的层错能.分析了Ni-Al-Ta/Mo合金中各元素浓度及温度对层错能的影响.结果表明:Ni-Al-Ta/Mo合金的层错能随Al含量的增加而明显降低,其中,随Al浓度提高,合金中原子偏聚自由能(ΔGγ→εs)降低,可促进γ′有序相的形成是使合金层错能降低的主要原因.随Mo/Ta含量的提高,可引起置换原子自由能(ΔGγ→εb)降低,原子偏聚自由能(ΔGγ→εb)升高;随温度提高,Ni-Al-Ta/Mo合金中的置换原子自由能(ΔGγ→εb)增加,表明合金中发生原子置换需要外部供给能量,而引起原子偏聚自由能(ΔGγ→εs)升高,表明高温不利于溶质原子的偏聚. 相似文献
974.
Herbert I. M. Lichtenegger Helmut Lammer Yuri N. Kulikov Shahin Kazeminejad Gregorio H. Molina-Cuberos Rafael Rodrigo Bobby Kazeminejad Gottfried Kirchengast 《Space Science Reviews》2006,126(1-4):469-501
The heating of the upper atmospheres and the formation of the ionospheres on Venus and Mars are mainly controlled by the solar
X-ray and extreme ultraviolet (EUV) radiation (λ = 0.1–102.7 nm and can be characterized by the 10.7 cm solar radio flux).
Previous estimations of the average Martian dayside exospheric temperature inferred from topside plasma scale heights, UV
airglow and Lyman-α dayglow observations of up to ∼500 K imply a stronger dependence on solar activity than that found on
Venus by the Pioneer Venus Orbiter (PVO) and Magellan spacecraft. However, this dependence appears to be inconsistent with
exospheric temperatures (<250 K) inferred from aerobraking maneuvers of recent spacecraft like Mars Pathfinder, Mars Global
Surveyor and Mars Odyssey during different solar activity periods and at different orbital locations of the planet. In a similar
way, early Lyman-α dayglow and UV airglow observations by Venera 4, Mariner 5 and 10, and Venera 9–12 at Venus also suggested
much higher exospheric temperatures of up to 1000 K as compared with the average dayside exospheric temperature of about 270
K inferred from neutral gas mass spectrometry data obtained by PVO. In order to compare Venus and Mars, we estimated the dayside
exobase temperature of Venus by using electron density profiles obtained from the PVO radio science experiment during the
solar cycle and found the Venusian temperature to vary between 250–300 K, being in reasonable agreement with the exospheric
temperatures inferred from Magellan aerobraking data and PVO mass spectrometer measurements. The same method has been applied
to Mars by studying the solar cycle variation of the ionospheric peak plasma density observed by Mars Global Surveyor during
both solar minimum and maximum conditions, yielding a temperature range between 190–220 K. This result clearly indicates that
the average Martian dayside temperature at the exobase does not exceed a value of about 240 K during high solar activity conditions
and that the response of the upper atmosphere temperature on Mars to solar activity near the ionization maximum is essentially
the same as on Venus. The reason for this discrepancy between exospheric temperature determinations from topside plasma scale
heights and electron distributions near the ionospheric maximum seems to lie in the fact that thermal and photochemical equilibrium
applies only at altitudes below 170 km, whereas topside scale heights are derived for much higher altitudes where they are
modified by transport processes and where local thermodynamic equilibrium (LTE) conditions are violated. Moreover, from simulating
the energy density distribution of photochemically produced moderately energetic H, C and O atoms, as well as CO molecules,
we argue that exospheric temperatures inferred from Lyman-α dayglow and UV airglow observations result in too high values,
because these particles, as well as energetic neutral atoms, transformed from solar wind protons into hydrogen atoms via charge
exchange, may contribute to the observed planetary hot neutral gas coronae. Because the low exospheric temperatures inferred
from neutral gas mass spectrometer and aerobraking data, as well as from CO+
2 UV doublet emissions near 180–260 nm obtained from the Mars Express SPICAM UV spectrograph suggest rather low heating efficiencies,
some hitherto unidentified additional IR-cooling mechanism in the thermospheres of both Venus and Mars is likely to exist.
An erratum to this article can be found at 相似文献
975.
976.
977.
978.
真空聚苯乙烯泡沫绝热材料用于制冷保温节能效果的实验研究 总被引:1,自引:0,他引:1
通过对真空聚苯乙烯泡沫和聚胺脂进行对比实验和理论分析,证明了作为制冷保温绝热材料,真空聚苯乙烯泡沫的保温绝热效果明显优于聚胺脂。 相似文献
979.
根据2000年第31届ICT国际年会的报告及交流内容,结合近年来国内外的有关文献报道,对新型含能材料及其在推进剂中应用的研究,按照高能氧化剂、含能粘合剂、高能燃料等分别进行了较详细的介绍和述评。 相似文献
980.