相变温控技术在航天热控领域中的应用现状及展望

由相变储能技术发展而来的相变温控技术作为一种新兴热控技术越来越受到航天领域的广泛关注。分析了相变温控技术及相变材料在热控领域的研究现状,对一种含有Cerrolow-136合金的相变温控装置进行温控实验。结果表明,金属类相变材料具有导热性好、密度大、化学性质稳定等特点,更适合应用于相变温控领域。最后展望了含金属相变材料相变温控装置在航天热控领域的应用前景,提出了潜在的研究方向。

高铬铸铁变温马氏体相变与摩擦诱发马氏体相变关系的研究

对三种含Mn、Si、Mo亚共晶高铬铸铁的变温马氏体相变进行了DSC分析,并对表层的摩擦诱发马氏体做了X射线衍射分析。结果表明,变温马氏体相变前期,马氏体形核、长大阻力较大。在M_s温度相近的情况下,变温马氏体相变形核、长大速率快的,其摩擦诱发马氏体量也多。

材料力学性质细观各向异性对变温马氏体相变瞬态温度场影响的计算分析

变温马氏体相变是重要相变,其温度场的计算是相变模拟关键环节.本文通过有限元方法计算,分析了材料力学性质细观各向异性对温度场的影响.结果表明:材料力学性质细观各向异性对温度场分布有影响,但对于45#钢这类材料,材料力学性质细观各向异性对其影响不大.

基于细观各项异性弹塑性理论的变温马氏体相变的数值模拟

马氏体相变是改善钢铁材料力学性能的1种重要途径。本文考虑了晶粒的随机分布(即细观各项异性),在0-1相变模型的基础上,采用热弹塑性有限单元法,以45#细长钢棒的淬火处理为例,进行了变温马氏体相变的数值模拟。

螺旋管内天然气冷凝流动传热数值模拟

针对螺旋管内天然气混合工质冷凝过程,在Lee模型的基础上,引入温度滑移因子,提出一种变温相变新模型,分别用新模型和Lee模型进行不同压力工况下的冷凝流动换热模拟。结果表明,新模型计算得到的温度沿流动方向下降很明显,反映了天然气温度滑移的影响,可以更好地反映出实际天然气冷凝过程中的物性变化,气液两相分布图中可明显观测到二次流扰动现象。为了同时考虑质量扩散热阻的影响,用Silver方法修正了新模型的模拟结果,修正后平均传热系数值与试验测定值的误差在10.7%~14%,预测精度优于Lee模型25%的误差精度。修正后的变温相变新模型适用于螺旋管内天然气混合工质的冷凝流动传热计算。

Isothermal and athermal type martensitic transformations in yttria doped zirconia

The phase transformation from the high temperature tetragonal phase to the low temperature monoclinic phase of zirconia had been long considered to be a typical athermal martensitic transformation until it was recently identified to be a fast isothermal transformation. The isothermal nature becomes more apparent when a stabilizing oxide, such as yttria, is doped, by which the transformation temperature is reduced and accordingly the transformation rate becomes low. Thus it becomes easy to experimentally establish a C-curve nature in a TTT （Time-Temperature-Transformation） diagram. The C-curve approaches that of well known isothermal transformation of Y-TZP （Yttria Doped Tetragonal Zirconia Polycrystals）, which typically contains 3mol% of Y2O3.In principle, an isothermal transformation can be suppressed by a rapid cooling so that the cooling curve avoids intersecting the C-curve in TTT diagram. Y-TZP is the case, where the stability of the metastable tetragonal phase is relatively high and thus the tetragonal phase persists even at the liquid nitrogen temperature. On the other hand, the high temperature tetragonal phase of pure zirconia can never be quenched-in at room temperature by a rapid cooling; instead it always turns into monoclinic phase at room temperature. This suggests the occurrence of an athermal transformation after escaping the isothermal transformation, provided the cooling rate was fast enough to suppress the isothermal transformation. Thus, with an intermediate yttria composition, it would be possible to obtain the tetragonal phase which is not only metastable at room temperature but athermally transforms into the monoclinic phase by subzero cooling. The objective of the present work is to show that, with a certain range of yttria content, the tetragonal phase can be quenched in at room temperature and undergoes isothermal transformation and athermal transformation depending on being heated at a moderate temperature or under-cooled below room temperature. Because both of the product phases are essentially the same monoclinic phase, both transformations are regarded as martensitic transformation, i.e. isothermal and athermal martensite. In some steels such as Fe-Mn-Ni and Fe-Ni-C, the occurrence of both isothermal and athermal martensitic transformations has been reported. However, in these cases, the isothermal transformation occurs at temperatures slightly above the Ms （Martensite start） temperatures, and thus these transformations are considered to conform the same C-curve. On the other hand, the Ms temperature of the present material is well below the C-curve, which suggests that completely different mechanisms are controlling the kinetics of these two modes of transformations. Other aspects on these transformations are also to be reported..

Transitional Process of Ploy（N-isopropylacrylamide） in Deuterated Solution

The fast phase-transitional process of ploy（N-isopropylacrylamide） （PNIPAM） in deuterated solution was studied by laser induced temperature jump technique combined with time-resolved mid-infrared absorbance difference spectroscopy on nanosecond level. The multi-peaks of amide I＇band of PNIPAM among the energy range of 1565-1700 cm^-1 was experimentally resolved to three groups （i, ii, iii） for the first time, while the distinct threestage procedure in the phase transitional process of long-chain PNIPAM was observed firstly too. Furthermore, proper assignments were also made for the three group peaks in amide I＇band and the three steps in the kinetics process of long-chain PNIPAM.

Interannual Variability of Sea Surface Temperature in the Northern Indian Ocean Associated with ENSO and IOD

The Northern Indian Ocean （NIO） sea surface temperature （SST） warming, associated with the E1 Nifio/Southern Oscillations （ENSO） and the Indian Ocean Dipole （IOD） mode, is investigated using the International Comprehensive Ocean-Atmosphere Data Set （ICOADS） monthly data for the period 1979-2010. Statistical analy- ses are used to identify respective contribution from ENSO and IOD. The results indicate that the first NIO SST warming in September-November is associated with an IOD event, while the second NIO SST warming in spring-summer following the mature phase of ENSO is associated with an ENSO event. In the year that IOD co-occurred with ENSO, NIO SST warms twice, rising in the ENSO developing year and decay year. Both short- wave radiation and latent heat flux contribute to the NIO SST variation. The change in shortwave radiation is due to the change in cloudiness. A cloud-SST feedback plays an important role in NIO SST warming. The latent heat flux is related to the change in monsoonal wind. In the first NIO warming, the SST anomaly is mainly due to the change in the latent heat flux. In the second NIO warming, both factors are important.

Dual fermion condensate and phase transition in QED_3

In this paper,we investigate the behaviors of dual fermion condensate in QED 3 under variation of temperature.By means of Dyson-Schwinger equation for the fermion propagator,we extract the dual fermion condensate and compare its behavior with the ordinary chiral fermion condensate and the chiral susceptibility.It is found that the dual fermion condensate cannot be regarded as the order parameter for the confinement-deconfinement phase transition in QED 3.Furthermore,the change of the dual fermion condensate around the chiral phase transition point observed in the present work must therefore be interpreted as solely induced by the chiral transition.

A thermally tunable terahertz bandpass filter with insulator- metal phase transition of VO_2 thin film

A terahertz bandpass filter with the sandwich structure consisting of thermally tunable vanadium dioxide(VO2) thin film,silica substrate and subwavelength rectangular Cu hole arrays is designed and theoretically analyzed.The results show that the transmittance of the filter can be actively tuned by controlling the temperature of VO2,the narrow band terahertz(THz) waves with the transmittance from 85.2% to 10.5% can be well selected at the frequency of 1.25 THz when the temperature changes from 50 ℃ to 80 ℃,and the maximum modulation depth of this terahertz bandpass filter can achieve 74.7%.