共查询到20条相似文献,搜索用时 15 毫秒
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The paper studies the process of floating a gas hydrate particle in liquid. The typical depths when gas bubble floating is accompanied by gas hydrate formation (or with zero gain of hydrate) were calculated. The low depths were identified when floating occurs with hydrate dissociation. The model assumes that the gas hydrate formation is limited by heat transfer from interface to the surrounding liquid. The model for gas hydrate dissociation assumes the rate governed by thermal conductivity of hydrate particle and by convective heat transfer to surrounding water. The temperature of the gas hydrate surface equals the phase transition temperature at the given water pressure. Comparative analysis of thermal conductivity and convective heat transfer effects on hydrate dissociation rate was performed for different initial radius of the particle. 相似文献
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Predicting clathrate hydrate phase equilibria is of interest in the area of natural gas exploitation. This proof of concept study presents the application of a simple lattice gas model and classical density functional theory coupled with van der Waals-Platteeuw theory to predict clathrate hydrate phase equilibria for several different hydrate-forming gas species. The dissociation pressure curve is predicted using adsorption isotherms predicted for the gas species in the crystal hydrate lattice. Comparisons are made between predicted phase equilibria (and other properties) and available experimental data. 相似文献
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A theoretical model for the processes of dissolution and hydrate formation behind a shock wave in a gas-liquid medium with
allowance for convective and molecular gas diffusion in the liquid and convective and conductive heat transfer caused by heat
release at the interphase boundary due to dissolution and hydrate formation is proposed. A comparison of the model calculations
with experimental data is made. 相似文献
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《中国科学:物理学 力学 天文学(英文版)》2010,(8)
Thermally induced evolution of phase transformations is a basic physical-chemical process in the dissociation of gas hydrate in sediment (GHS). Heat transfer leads to the weakening of the bed soil and the simultaneous establishment of a time varying stress field accompanied by seepage of fluids and deformation of the soil. As a consequence, ground failure could occur causing engineering damage or/and environmental disaster. This paper presents a simplified analysis of the thermal process by assuming that thermal conduction can be decoupled from the flow and deformation process. It is further assumed that phase transformations take place instantaneously. Analytical and numerical results are given for several examples of simplified geometry. Experiments using Tetra-hydro-furan hydrate sediments were carried out in our laboratory to check the theory. By comparison, the theoretical, numerical and experimental results on the evolution of dissociation fronts and temperature in the sediment are found to be in good agreement. 相似文献
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用分子动力学模拟方法研究甲烷水合物的热激法,化学试剂法,以及热激法结合化学试剂法分解,系统研究温度为277K和340K时添加液态水(WTR)和30wt%乙二醇(EG)溶液对水合物分解的影响.模拟显示WTR与水合物表面水分子形成氢键,破坏水合物原有的氢键平衡,造成笼状结构坍塌,水合物分解.EG分子中的羟基与水合物表面水分子形成氢键,从而破坏原有的稳定结构,造成水合物笼状结构被破坏,达到促进水合物分解,释放甲烷气体的效果.比较温度为277K和340K时添加WTR和30wt%EG溶液对水合物分解效果得出EG(340K)> WTR(340K)>EG(277K)>WTR(277K),热激法结合化学试剂法能更好促进水合物分解. 相似文献
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水流动强化天然气水合物降压分解研究 总被引:1,自引:0,他引:1
降压法被认为是最经济可行的天然气水合物开采方法,但开采后期驱动力不足、甚至产生水合物的二次生成,因此其应用受到限制。本文将降压法与水流动结合提升水合物分解驱动力,研究不同降压模式和水流动对天然气水合物分解特性的影响。发现当降压结合水流动时,压降为水合物分解提供初始驱动力,且压降越大水合物分解驱动力越大。同时水流动能够加快传热传质过程,为水合物分解提供额外的驱动力。在快速降压结合水流动模式中,较高背压下水流动为水合物分解提供主要的驱动力;在梯度降压结合水流动模式中,降压和水流动共同为水合物提供分解驱动力,对水合物分解的促进作用更加显著。 相似文献
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V. E. Nakoryakov S. Ya. Misyura S. L. Elistratov A. Yu. Manakov A. A. Sizikov 《Journal of Engineering Thermophysics》2013,22(3):169-173
Kinetics of dissociation of synthetic and natural methane gas hydrates, and also double isopropanol-methane hydrate is investigated. Thermal fields of the sample surfaces are measured by means of thermal imaging in combustion of released methane with clathrate dissociation. The dissociation rates of natural hydrate and double hydrate with isopropanol are many times lower than those of synthetic methane hydrate. Methane combustion is accompanied by formation of a thin water film on the powder surface, which has a strong effect on the heat and mass transfer mechanisms. The experiments demonstrated partial self-preservation for methane hydrate and the absence of self-preservation for double isopropanol-methane hydrate. The experimentally observed dissociation rate of double isopropanol-methane hydrate is considerably lower than that of methane hydrate. 相似文献
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V. Sh. Shagapov Yu. A. Yumagulova O. A. Shepelkevich 《Thermophysics and Aeromechanics》2016,23(4):537-542
The solution was obtained for a problem of gas hydrate growth in water with dissolved gas. The rate of hydrate formation depends on gas diffusion to the contact with gas hydrate. Three versions of problem configuration were considered: planar, radial, and spherical symmetry. For these cases, the values of the self-similarity coordinate were obtained: this parameter controls the growth of gas hydrate in water with gas dissolved and the level of top temperature in the hydrate zone. Analysis was performed for temperature fields related to heat release during hydrate formation. 相似文献
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Hydrate plugging is a hidden threat to the safe exploitation of oil and gas. Inorganic salts are widely used as thermodynamic inhibitors to effectively prevent the hydrate formation. This study uses a molecular dynamics method to explore the mechanism of the hydrate dissociation via inorganic salts on the micro-scale. We simulated the dissociating process of methane hydrate under different concentration series of NaCl, KCl and CaCl2 solutions at 273 K, and analysed the changes of ionic structure, transport parameters and kinetic energy in the system of inorganic salt/hydrate. The simulation results successfully revealed the step-by-step dissociation of hydrate, and the differences in dissociation rates among the different inhibitors. The energy needed for hydrate dissociation alters for different inorganic solutions; the energy reaches maximum when KCl is the inhibitor, and lowest when the concentration of CaCl2 exceeds 30% w/w. We calculated the coordination numbers of all components, including oxygen atoms, cations and anions, and also their diffusion coefficients; analysed the effects of the three inorganic salts on the simulated hydrate structure and its transport; in addition, investigated the mechanism of hydrate dissociation via inorganic salts. 相似文献
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After obtaining experimental data of CO2 hydrate formation and dissociation in a porous medium using magnetic resonance imaging (MRI), the purpose of this study was to analyze the different dissociation rate of CO2 hydrate using two heating rates. Images were obtained by using a fast spin-echo sequence, and the field of view was set to 40×40×40 mm. The vessel pressure was monitored during hydrate formation and dissociation, which was used to compare with MRI mean intensity. The result indicated that the MRI could visualize hydrate formation and dissociation, and the MRI mean intensity of water was in good agreement with the vessel pressure changes. The hydrate formation and dissociation rates were also quantified using the MRI mean intensity of water. The experimental results showed that the higher heating rate caused the rapid hydrate dissociation. 相似文献
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S. Ya. Misyura 《Journal of Engineering Thermophysics》2018,27(2):191-195
The kinetics of dissociation of methane hydrate in air at an external pressure of 1 bar was experimentally studied. It is shown that to describe the mechanism of dissociation of gas clathrate, it is necessary to take into account not only the degree of deviation of temperature and pressure from equilibrium values, but also the diameter of granules. As the diameter decreases, the rate of decomposition of methane hydrate increases significantly. Change in the grain size affects formation of pores and dissociation. The experiment demonstrated a self-preservation mechanism for granule diameters of more than 1 mm. In the case of powder with an average diameter of less than 0.3 mm, there was no self-preservation. The rate of dissociation depends on the combined effect of diffusion, crystallization, and creep. 相似文献
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Using the first-principles method based on the density functional theory(DFT),the structures and electronic properties of different gas hydrates(CO_2,CO,CH_4,and H_2) are investigated within the generalized gradient approximation.The structural stability of methane hydrate is studied in this paper.The results show that the carbon dioxide hydrate is more stable than the other three gas hydrates and its binding energy is-2.36 e V,and that the hydrogen hydrate is less stable and the binding energy is-0.36 e V.Water cages experience repulsion from inner gas molecules,which makes the hydrate structure more stable.Comparing the electronic properties of two kinds of water cages,the energy region of the hydrate with methane is low and the peak is close to the left,indicating that the existence of methane increases the stability of the hydrate structure.Comparing the methane molecule in water cages and a single methane molecule,the energy of electron distribution area of the former is low,showing that the filling of methane enhances the stability of hydrate structure. 相似文献
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The mathematical model of decomposition of a spherical gas hydrate particle in water behind a 1D wave of the stepped profile
(rarefaction wave) is suggested. Contribution of the outer and inner heat flux in a particle to the process of hydrate decomposition
is studied. The effect of the gas hydrate particle size, pressure and temperature jumps in liquid on gas hydrate decomposition
is investigated. 相似文献
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R. K. Zhdanov T. P. Adamova O. S. Subbotin A. A. Pomeranskii V. R. Belosludov V. R. Dontsov V. E. Nakoryakov 《Journal of Engineering Thermophysics》2010,19(4):282-288
The properties of methane + ethane and methane + propane hydrates of cubic structures sI and sII are theoretically investigated.
It is shown that the composition of the formed binary hydrate strongly depends on the percentage of a heavier guest in gas
phase. For instance, for a 1% molar ethane concentration in gas phase, even at a low pressure, ethane occupies 60% large cavities
in the hydrate sII, and as the pressure grows to 100 atm, it occupies 80% large cavities at a low temperature. The tendency
remains the same at a temperature of higher than the ice melting point, but the methane concentration in the hydrate decreases
to 30%. In the structure sI, the influence of the component composition of the gas mixture on that of the formed hydrate is
less evident. However, in this case, calculation showed also that for a 1% molar ethane concentration in gas phase, ethane
molecules occupy from 8 to 10% large hydrate cavities, depending on the pressure. This work is concerned with modeling phase
transitions between cubic structures sI and sII of methane + ethane binary hydrates in view of incomplete occupation of cavities
in the hydrate by guest molecules. For an ethane concentration under 2% in the gas mixture, the structure sII becomes more
thermodynamically stable than the structure sI. However, as the ethane concentration grows to 20% in the equilibrium ice-gas-hydrate
and to 40% in the equilibrium water-gas-hydrate, the structure sI becomes more thermodynamically stable. Hence, for low ethane
concentrations in a gas mixture, the structure sI can be formed only as a metastable phase. Phase equilibria of methane hydrate
sI and mixed methane + propane hydrate sII are considered, depending on the gas phase composition. Similar results are obtained
for this equilibrium; this can evidence simultaneous formation of hydrates sI and sII at low propane concentrations. 相似文献