共查询到18条相似文献,搜索用时 312 毫秒
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CO2置换开采天然气水合物以及水合物法气体储运技术是当前科学家们研究的热点,而水合物的稳定性对其长时间储存和长距离运输至关重要。因此必须提高二氧化碳水合物储存能力和寻求水合物高效稳定的储存条件,然而科学家们发现一些促进剂可以使水合物在温和的条件下长时间存储。本文从“自保护”效应的3种机制、温度、压力以及粒径、促进剂和水合物形态这些因素分析了其对二氧化碳水合物稳定性的影响,证明气体水合物普遍在260~270K和0.1~0.4MPa的条件下稳定性较好,并且同种促进剂在冰点上下对水合物稳定性的影响不同,最后指出了水合物稳定性方面今后的研究方向。 相似文献
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水合物的生长和分解规律对开发海洋天然气水合物资源,实现深水天然气水合物气液固多相管道输送都具有重要意义。为了进一步揭示水合物的生长和分解特性,本文采用高压全透明反应釜装置,进行了温度0~30℃、压力3.35~8.16MPa和搅拌速率200~1000r/min范围内的16组甲烷水合物生长和分解动力学实验研究。结果表明:实验过程可分为水合物诱导期、快速生长期、缓慢生长期以及分解期这4个阶段。在水合物快速生长阶段,获得了温度、压力、搅拌电机扭矩和水合物生长速率随时间的变化规律,观察到了水合物颗粒的均相和非均相分布状态。通过加热促使水合物分解,揭示了分解阶段温度、压力和分解速率等关键参数的变化规律以及水合物块的分解形态。分析表明,水合物颗粒的分布状态与水合物浆液的流动性直接相关;水合物块的静态分解过程受到分解气传质控制。 相似文献
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二氧化碳置换法开发天然气水合物的实验研究 总被引:1,自引:0,他引:1
考察了温度在270.15~278.15 K,压力在2.3~4.0 MPa条件下应用CO2置换天然气水合物中CH4的置换过程.结果表明,温度和压力是置换反应速度和效率的重要影响因素.温度和压力越高,越有利于反应的进行.而压力的影响没有温度的影响明显.同时,置换过程中进入水合物相的二氧化碳的摩尔量与气相中CH4增加的摩尔量的比率超过了1:1,这可能是由于纯水水合物的甲烷含气量并未达到理论含气量,置换的同时有部分二氧化碳分子进入水合物的空孔穴和游离水中,形成二氧化碳水合物和水溶液. 相似文献
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利用自行搭建的热线法液体热导率和热扩散系数装置测试了两种咪唑型离子液体([C6mIm][BF4]和[C4mIm][BF4])在不同温度下的热导率和热扩散系数。根据文献报道的密度数据获得了样品的比热容。结果表明:两种离子液体的热导率与温度的相关性不大;两种阳离子结构相似的离子液体热扩散率相近, 热扩散率随温度的升高有明显的变化, 本文认为离子液体内部的离子动量分布与温度紧密相关, 离子间的动量交换随温度的升高而增加, 离子动量分布随温度升高逐渐趋于一致, 离子间碰撞产生的动量交换不再明显改变离子的动量, 导致热扩散率的变化随温度升高而减小。 相似文献
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采用分子动力学模拟方法Green-Kubo理论计算了263.15 K、3 MPa,sⅠ乙烷水合物、乙烯水合物的导热,给出密度和热导率值。从主客体分子和晶体结构(致密性、规整程度)对导热的影响等角度研究了烃类水合物(甲烷水合物、乙烷水合物、乙烯水合物)导热的特性。结果显示化学性质相似、分子量相差不大的烃类形成的水合物,其导热具有相似的温度压力依赖关系和晶体结构相关关系。对于sⅠ型水合物,水分子对水合物导热的影响远远超过客体分子对导热的影响。水合物的分子量越大,水合物密度越大,热导率越大。水合物晶体越致密、晶格越规整,热导率越大。 相似文献
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A study on the apparent thermal conductivity of polyurethane foam was carried out. A HCFC (hydrochlorofluorocarbon) gas and carbon dioxide were used as the physical blowing agent and ultrasonic excitation was applied to increase the rate of bubble nucleation. The thermal conductivity of the binary gas mixture was predicted theoretically to estimate the apparent thermal conductivity of the polymer foam. Effects of conduction and radiation on the apparent thermal conductivity of the cellular polyurethane were considered with respect to the cell size and the effect of convection was neglected because of the small cell size. A laboratory RIM machine was designed and built for foaming experiments. The foaming experiments were performed at various processing conditions, and density, apparent thermal conductivity, number of cells, and cell sizes were measured. Best results such as low thermal conductivity and small bubbles were obtained when the polyol was mixed with the HCFC gas and saturated with carbon dioxide at 0.3 MPa, and foamed with ultrasonic nucleation. 相似文献
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The new experimental apparatus capable of observing the clathrate hydrate formation kinetics was developed in this study.
Experimental data on the kinetics of carbon dioxide hydrate formation were carefully measured. The experiments were carried
out in a semi-batch stirred tank reactor with stirring rate of 500 rpm at three different temperatures between 275.2 and 279.2
K and at pressures ranging from 2.0 to 3.5 MPa. The kinetic model was adopted to predict the growth of hydrates with only
one adjustable parameter which represented the rate constant for the hydrate particle growth. The model was based on the crystallization
theory coupled with the two-film theory for gas absorption into the liquid phase. The model predictions matched the experimental
data very well with the largest deviation of 7.18%, which is within experimental error range. This study is the first for
the kinetic data of carbon dioxide hydrate formation and important in developing carbon dioxide fixation process using clathrate
hydrate phenomenon. 相似文献
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《分离科学与技术》2012,47(15):2498-2506
ABSTRACTA series of experiments on CO2 hydrate formation were carried out in the presence of titanium dioxide (TiO2), silicon dioxide (SiO2), multi-walled carbon nanotubes (MWNTs) nanoparticles. The effects of these nanoparticles on induction time, final gas consumption, and gas storage capacity have been investigated at the temperature of 274.15 K and the initial pressure of 5.0 MPa.g. The induction time of CO2 hydrate formation was remarkably shortened to 12.5 min in the presence of 0.005 wt% MWNTs nanoparticles. The high thermal conductivity and heat capacity of MWNTs nanoparticles presented better heat transfer, and large surface area provided more suitable sites for heterogeneous nucleation of CO2 hydrate. 相似文献
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V.P. Melnikov A.N. Nesterov A.M. Reshetnikov V.A. Istomin 《Chemical engineering science》2011,66(1):73
In this study, the dissociation of isolated carbon dioxide hydrate particles of sizes in the range 0.25–2.5 mm was investigated. It was found that below the ice melting point, the hydrates dissociated into supercooled water (metastable liquid) and gas. The formation of the liquid phase during CO2 hydrate dissociation was visually observed, and the pressures of the hydrate dissociation into supercooled water and gas were measured in the temperature range 249–273 K. These pressures agreed well with the calculated data for the supercooled water–hydrate–gas metastable equilibrium (Istomin et al., 2006). In the P–T area on the phase diagram bounded by the ice–hydrate–gas equilibrium curve and the supercooled water–hydrate–gas metastable equilibrium curve, hydrates could exist for a long time because the metastable phase and their stability are not connected to the self-preservation effect. The growth of the metastable CO2 hydrate film on the surface of supercooled water droplets formed during the hydrate dissociation was observed at pressure above the three-phase supercooled water–hydrate–gas metastable equilibrium pressure but still below the three-phase ice–hydrate–gas equilibrium pressure. It was found that the growth rate of the metastable CO2 hydrate film was higher by a factor of 25 and 50 than that for methane hydrate and propane hydrate, respectively. 相似文献
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Philip H. McCluskey Robert K. Williams Ron S. Graves Terry N. Tiegs 《Journal of the American Ceramic Society》1990,73(2):461-464
Thermal diffusivity and conductivity values for several Al2 O3 -SiC whisker composites were determined. The thermal diffusivity values spanned the range from 373 to 1473 K, and thermal conductivity data wre obtained between 305 and 365 K. The thermal diffusivity decreased with increasing temperature and increased with SiC-whisker content. An estimate of the thermal conductivity of the whiskers was obtained from the direct thermal conductivity measurements, but attempts to derive whisker conductivity values from the thermal diffusivity data were not successful because the laser flash method lacks the required accuracy and precision. Specimens were subjected to two different thermal quench experiments to investigate the effect of thermal history on diffusivity. In the most severe case, multiple 1073- to 373-K quenches, radial cracks were observed in the test specimens; however, there was no change in diffusivity. The lack of sensitivity to thermal cycling appears to be related to the sample size. 相似文献
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《Journal of the European Ceramic Society》2005,25(4):393-400
Better thermal insulation of the hot path components is needed in state-of-the-art gas turbines and diesel engines, because of the increasing demands of the higher process temperatures. In these processes, thermal barrier coatings (TBCs) and various cooling techniques mainly control the component surface temperatures. For this reason low thermal conductivity of the TBCs are extensively studied. One of the main factors determining the TBC thermal conductivity is the coating microstructure, with specific attention to the porosity content, as well as to its morphology and orientation. One important feature of TBCs is the stability of their thermal properties as a function of time at service conditions. In fact the prolonged exposure to high temperature can promote shrinkage phenomena within the TBC, which make the coating less strain tolerant and more heat conductive. This leads to a drastic reduction of the functional effectiveness of this ceramic protective top layer.In order to study the evolution of thermal properties of TBC, as a function of time and temperature, thermal diffusivity evaluation by laser flash method has been performed. The measurements have been performed on freestanding yttria-stabilized zirconium oxide (YPSZ) TBCs. In particular, measurements have been carried out at five different temperatures in the range 900–1300 °C, for different ageing times (from 1 up to 150 h). The data show a significant increase of the thermal diffusivity also after exposures of few hours, especially at the highest testing temperatures. Microstructural analysis carried out by optical and electron microscopy clearly showed that the observed thermal diffusivity variations can be ascribed to sub-micrometric crack healing and sintering neck formation. Mechanical testing confirmed the microhardness increase of TBC as well. Finally the data have been summarised in order to experimentally define a “functional life” curve of the TBC, as a function of ageing time and temperature. 相似文献
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Guochang Zhang 《Chemical engineering science》2008,63(8):2066-2074
This paper details creation of methane sI hydrates that are much more stable at 1 atm and 268.2 K than any previously reported. Extraordinarily stable natural gas sII hydrates at 1 atm and 268.2-270.2 K are reported for the first time. Test innovations that achieved ultra-stabilities give insight into hydrate self-preservation mechanisms. Water-surfactant liquid solutions were used to nucleate hydrate crystals that adsorbed as extremely small particles on surfaces of high thermal conductivity. The small hydrate particles packed and consolidated symmetrically upon Al or Cu cylindrical surfaces, minimizing internal void spaces and fractures in the accumulated 250-400 g hydrate mass. Resulting hydrate stability window is 268.2-270.2 K at 1 atm. Methane sI, as well as natural gas sII, hydrates exhibit only minimal decomposition upon reducing confining system pressure to 1 atm in the 268.2-270.2 K stability window. Total gas that evolved after 24 h at 1 atm in the stability window typically amounted to less than 0.5% of originally stored gas, and this ultra-stability was shown to persist when the test was allowed to run 256 h before terminating. The entire methane sI or natural gas sII hydrate mass remains stable during pressure reduction to 1 atm, whereas previous reports defined hydrate anomalous stability for only about 50% of fractional hydrate remnants. 相似文献
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S. Takeya M. Kida H. Sakagami N. Takahashi V. Soloviev N. Biebow A. Salomatin 《Chemical engineering science》2006,61(8):2670-2674
We report on the structural properties of natural gas hydrate crystals from the Sea of Okhotsk. Using powder X-ray diffraction (PXRD), it was determined that sediments from four locations contained type I gas hydrate, which encage mostly methane (96-98%) and a small amount of carbon dioxide. For all hydrates, the lattice constant was estimated to be at 113 K, which approximately equals that of pure methane hydrate. The result is in good agreement with the structure of artificially synthesized methane + carbon dioxide mixed-gas hydrates. These results suggest that the lattice constant of the natural gas hydrate does not change due to a change of CO2 gas content. In addition, the thermal expansion of the sampled hydrate was measured for the temperature range of 83-173 K, and the resulting density of the hydrate crystal at 273 K was estimated to be . These results are essential for applying natural gas hydrates as an alternative natural fuel resources. 相似文献