天然气水合物成藏体系研究进展

基于近年来国内外冻土区和海域天然气水合物勘探成果,从稳定条件、气源、气体运移、有利储层这几个方面概述了水合物成藏体系的新进展。研究结果表明,地温梯度、海底表层温度、气体组分、孔隙水盐度等多种因素影响并控制了水合物的相平衡条件。全球已发现的水合物气体来源以生物成因气、生物成因−热成因混合气为主,热成因气体对水合物成藏的贡献得到了越来越多的重视。烃类气体以扩散、溶解于水和独立气泡的形式在沉积物中发生迁移,断层、底辟、气烟囱构造等为含气流体运移提供了有效的通道。归纳出六种水合物的产出特征和四种水合物的储层类型。通过对水合物成藏模式的总结对比,认为以地质构造环境差异而进行的成藏模式分类具有更好的代表性。     

天然气水合物导热性能研究现状

天然气水合物导热系数的研究对于模拟自然界天然气水合物的成藏和天然气水合物勘探、开采具有重要意义。本文介绍了获取天然气水合物导热系数的实验测试和模拟计算方法,分析了气体水合物导热特性、导热机理以及水合物复合体系导热。总结了水合物导热规律,即外界温压条件和晶穴占有率对水合物的导热产生影响,且水合物的导热具有相似的温度压力依赖关系,并呈玻璃体的导热特性。水合物玻璃体导热特性由水合物笼型结构决定,而客体分子的存在强化了水合物导热的玻璃体属性。指出非稳态下天然气水合物导热性能变化研究对分析天然气水合物在常压下的稳定性、确定甲烷水合物等最佳储存温度、从导热角度探讨自保护效应机理等具有重要意义。     

基于VB语言的水合物相平衡预测软件开发研究

为了对天然气水合物相平衡进行相关研究,实现对不同压力（温度）条件下水合物临界生成温度（压力）的迅速计算,有必要研究和开发天然气水合物相平衡预测软件.利用VB语言面向对象可视化的特点,并结合分子热力学模型法,编制纯水中水合物相平衡预测软件;同时利用软件对混合组分气体生成水合物的相平衡进行分析比较.软件界面简洁,操作简单,通过简单的输入输出操作,可在短时间内完成相应的计算.结果表明,软件对于混合组分天然气水合物的相平衡预测较为准确,其相对误差控制在1％以内,对工程实践有较强的指导意义.     

布莱克海台天然气水合物油气系统

系统论成为水合物成藏研究的趋势,水合物的勘探活动证明,海域水合物的形成不仅受到温度、压力、水深等条件的影响,其产出状态和分布规律还受到气体组分、气体来源、沉积条件、流体运移条件等的控制。以布莱克海台作为主要研究区域,运用天然气水合物油气系统的方法,通过对这一区域水合物稳定条件、气体组分和来源、有利沉积体特征和含气流体运移等方面进行分析,总结了其水合物油气系统的特征。研究结果表明,布莱克海台区域温度和压力等条件非常适合水合物的形成,丰富的生物成因气体是水合物形成的主要气体来源,强烈的等深流沉积和区域背斜构造对水合物的形成相当有利,为水合物的赋存提供了潜在的储集类型和聚集空间等有利的沉积体系,盐底辟、断层等为含气流体的运移提供了有利的通道。利用水合物油气系统,有利于指导我国南海水合物勘探研究工作,以便最终解决南海水合物在哪里富集,以及规模成藏等关键问题。     

甲烷水合物及其沉积层导热特性的研究现状

总结了近年来国内外甲烷水合物及其沉积层导热特性的研究现状,从实验测试和模拟研究两方面分析了甲烷水合物及其沉积层的导热影响因素、相关规律和导热机理。研究结果表明：纯质水合物的导热性能与外界温度、压力、客体分子数量、多孔介质、笼形结构等因素有关,其值大小主要由主体水分子形成的笼形结构决定;而水合物沉积层导热系数的大小主要依赖于实验样品的组成成分、初始水饱和度、各组分分布,与温度、压力以及垂直有效应力关系不大。最后,指出了现存研究方法中一些值得改进的地方,并对今后的研究工作进行了展望。     

应用于土遗址博物馆的太阳能照明装置光学性能研究

土遗址博物馆的照明是文物保护工作的重要内容之一,文章提出了一种太阳能照明装置,利用气泡对光线的散射作用来实现对土遗址博物馆的自然光照明。文章介绍了该照明装置的工作原理,并在光学暗室中对气泡幕的光线散射性能进行了性能测试,分析了气泡幕厚度、产生气泡的气体压力、入射光照度等对含气泡幕水体的光线透过率、侧表面照度的影响。结果表明,太阳光通过含气泡幕的水体可以对土遗址博物馆内进行照明,光线透过率随产生气泡的气体压力的增大而减小,侧表面照度随产生气泡的气体压力、入射光照度和水中高度的增大而增大,光线透过率与产生气泡的气体压力呈指数函数关系。     

气体水合物分解热的研究进展

气体水合物作为新一代蓄冷介质,在空调蓄冷领域有良好的应用前景.其分解热是重要的热物性之一,对蓄冷系统的设计至关重要.介绍了国内外气体水合物分解热的研究进展,列出了气体水合物分解热的测量、计算方法以及影响气体水合物分解热的主要因素和影响机理,并指出气体摩尔分数和添加剂摩尔分数均会影响水合物的分解热,且气体分子直径是影响水合物分解热的主要因素.研究为水合物的开采利用、稳定性研究以及蓄冷系统的设计提供了理论基础.     

具有线性温度分布的射流失稳研究

基于线性稳定性理论,针对具有线性温度分布的液体射流分裂过程,建立了射流扰动控制方程,给出了扰动方程在气/液分界面上应满足的边界条件,推导出了描述存在温度扰动的圆柱形液体射流自由表面三维扰动发展的色散关系;模型中同时考虑了空化气泡、射流周围气体的旋转以及射流和周围气体的可压缩性;对建立的数学模型及相应的求解方法进行了验证.在此基础上,分析了非轴对称扰动下具有线性温度分布的射流表面扰动波数和扰动增长率的演化,讨论了存在温度扰动时,空化气泡、气体旋转以及射流和气体可压缩性对射流稳定性作用的变化.结果表明:温度扰动的存在不仅会对液体射流稳定性产生较大影响,使得最大扰动增长率明显增大,扰动波波数范围显著拓宽,而且还会对空化气泡、气体旋转以及射流和气体可压缩性对射流稳定性的作用产生一定的影响.     

不同表面活性剂对甲烷水合物生成的影响

为探究表面活性剂对于水合物生成的促进机理,文章选取了阴离子表面活性剂十二烷基硫酸钠(SDS),阳离子表面活性剂十二烷基三甲基溴化铵(DTAB)和非离子表面活性剂脂肪醇聚氧乙烯醚(AEO)进行甲烷水合物的生成实验。测试了表面活性剂的特性(如临界胶束浓度)、表面活性剂溶液在反应釜内表面的润湿性对水合物生成过程的影响,并对DTAB进行搅拌增强实验。实验结果表明:以DTAB和AEO为促进剂时,促进机理为胶束作用,水合物在反应釜底部生成;以SDS为促进剂时,水合物在气/液/固三相交界处开始生成,由于形成多孔结构的水合物,可以利用毛细作用不断的促使反应液与气体保持接触,从而使其对水合物生长的促进效果更佳。     

微狭缝中甲烷吸附特性的分子动力学模拟

为了研究甲烷在纳米尺度狭缝中的吸附特性,采用分子动力学模拟的方法研究了温度、压力以及狭缝表面的水滴对甲烷吸附情况的影响。研究表明:降低温度和增大压力均能使吸附相的密度增大、吸附层的层数增加、吸附区扩大;升高压力将使吸附作用减弱,温度较低时,升高温度将使吸附作用增强,温度较高时,升高温度将使吸附强度减弱;狭缝表面存在水滴时,狭缝对甲烷的吸附作用被明显削弱。     

Influences of bubble formation on different types of heat exchanger fouling

In this paper, a systematic comparison is performed to investigate fouling of suspended particles under forced convective and subcooled flow boiling heat transfer. For this purpose, two different types of fouling are separately considered: crystallization fouling of dissolved CaSO₄ particles in water and particulate fouling of suspended Al₂O₃ particles in n–heptane. The effect of hydraulic parameters such as fluid velocity and also bubble generation under subcooled flow boiling are studied. Results of the experiments demonstrate that creation of boiling condition in the heat exchanger has opposite influence in these two types of fouling. It means that bubble generation on the heat transfer surface promotes scale formation under crystallization fouling. This is due to the fact that increased bubble generation creates higher supersaturation beneath the vapor bubble, therefore, increasing the crystal concentration in the boundary layer. On the other hand, boiling condition inhibits the scale formation under particulate fouling because the suspended particles are repelled from the boundary layer by the strong turbulences created by the swarm of bubbles.     

Injection and boiling of liquid CO2 with a hydrate coating

We elucidated the effect of a hydrate film on the CO₂ droplet size when the droplet was injected into high-pressure water. The factors that influence the droplet size and shape are the injection rate, nozzle diameter, temperature, and also the tension and propagation velocity of the hydrate thin film. We also found that the hydrate film on the droplet will promote the boiling of liquid CO₂ when the pressure decreases. These results can be applied to the release of liquid CO₂ droplets in the ocean for CO₂ sequestration: for example, when the drops rise above 500-m in the ocean, boiling due to decompression should occur.     

静态闪蒸过程汽泡生长的理论与实验研究

本文针对去离子水静态闪蒸时单汽泡的动态生长过程开展了可视化实验观察及理论分析，研究了过热度和闪蒸腔压力对汽泡生长的影响。理论模型考虑了汽泡成核点附近固体壁面对汽泡生长的影响，通过与实验结果的对比表明，壁面效应对汽泡生长影响显著，尤其是汽泡生长速率较小时，引入壁面效应后的理论模型能更好的与实验结果相吻合。通过分析汽泡生长过程的动力学特征可知，相同闪蒸腔压力但过热度较大时，汽泡生长过程具有较短的表面张力控制阶段，并在过渡阶段和传热控制阶段均具有较大的生长速率；而相同过热度但较小闪蒸腔压力时，汽泡在早期的惯性控制阶段生长速率较小，但在后期的传热控制阶段生长速率较大。     

A numerical study of air entrapment during the droplet impact on a solid substrate

A numerical investigation is conducted to study the air entrapment phenomenon when two different liquids such as water and diesel droplet are impacted on the solid surface. The beginning of the air entrapment process was observed during droplet impact on a solid substrate forming a dimple underneath the droplet. The air film thus trapped underneath the droplet started evolving into the air bubble. This journey of evolution mainly comprises phases like an inertial retraction of air film, contraction, and pinch-off of the secondary droplet inside the air bubble for a water droplet impact case. The volume of fluid approach has been utilized to track the progress of air film evolution. The influence of surface wettability has been observed on the evolution of air film into the air bubble by taking four different values of contact angle pertaining to the hydrophilic surface (θ = 10° and 35°) and hydrophobic surface (θ = 90° and θ = 120°). The air bubble was found to get detached from the substrate for the hydrophilic surface (θ = 35°) and observed to remain attached to the substrate for the hydrophobic surface. The variation of pressure underneath the droplet was also investigated as the droplet reaches the substrate. The effect of surface tension has been studied on the evolution of air film by impacting the diesel droplet on the same substrate keeping the same wettability condition (θ = 35°). The lower surface tension of the diesel droplet as compared to the water droplet delayed the process of air film evolution and consequently decreases the retraction speed of air film. Also, the air bubble remains attached to the surface. Furthermore, the air bubble detaches from the surface for an even higher wettability condition (θ = 10°). Thus surface wettability and surface tension become two important factors governing the development of entrapped air film and bubble elimination in many practical applications.     

Experimental investigation of bubble behaviors in subcooled flow boiling

The experimental investigation on vapor bubble growth is performed for analyzing subcooled boiling in a vertical annular channel with inner heating surface and upward water flow under atmospheric pressure. Bulk liquid mass flux ranges from 79 kg/m2s to 316 kg/m2s, and subcooling is from 40 K to 60 K. The bubble behaviors from inception to collapse are captured by High-speed photography. The performance of bubble growth recorded by the high-speed photography is given in this paper. The bubble behaviors, effect of the bubble slippage on the heat transfer, and various forces acting on the bubble are discussed.     

An experimental investigation on spreading of droplets with evaporation and nucleation

An experimental investigation was conducted to visually observe the dynamic characteristics of water droplets with evaporation and nucleation on stainless steel and polished silicon surfaces. The water droplet diameter, contact area, and spreading speed were measured using a high‐speed CCD camera at surface temperatures ranging from 110^°C to 190^°C, and a model was proposed to describe the dynamic behavior of droplet spreading. The spreading of water droplets under evaporation and nucleate boiling is highly dependent on the dynamic bubble behavior in the droplets, particularly bubble volume, bubble interaction, as well as the surface properties and temperature. Water droplets were easiest to spread at the surface temperature of 130 ^°C, and the spreading tendency increased with increasing surface coarseness. © 2008 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.20231     

Dynamic water transport and droplet emergence in PEMFC gas diffusion layers

The dynamics of liquid water transport through the gas diffusion layer (GDL) and into a gas flow channel are investigated with an ex situ experimental setup. Liquid water is injected through the bottom surface of the GDL, and the through-plane liquid pressure drop, droplet emergence and droplet detachment are studied. The dynamic behaviour of water transport in and on the surface of the GDL is observed through fluorescence microscopy, and the through-plane liquid pressure drop is measured with a pressure transducer. With an initially dry GDL, the initial breakthrough of liquid water in the GDL is preceded by a substantial growth of liquid water pressure. Post-breakthrough, droplets emerge with a high frequency, until a quasi-equilibrium liquid water pressure is achieved. The droplet emergence/detachment regime is followed by a transition into a slug formation regime. During the slug formation regime, droplets tend to pin near the breakthrough location, and the overall channel water content increases due to pinning and the formation of water slugs. Droplets emerge from the GDL at preferential breakthrough locations; however, these breakthrough locations change intermittently, suggesting a dynamic interconnection of water pathways within the GDL. The experiments are complemented by computational fluid dynamics (CFD) simulations using the volume of fluid method to illustrate the dynamic eruption mechanism.     

The Influence of System Pressure on Bubble Coalescence in Nucleate Boiling

Boiling is one of the most effective heat transfer mechanisms. In spite of a long time of research, the physical fundamentals are still not sufficiently understood. Pursuing the objective to predict heat transfer based on physical and geometrical properties, experimental and numerical investigations are conducted at the institute of the authors. The focus of the presented research is the coalescence of two single bubbles under varying pressure conditions. In the experiment a thin stainless-steel foil is used as a Joule heater. The experiments were performed in a pressure range of 300–1000 mbar using FC72 as working fluid. Two types of heaters with a distance between two artificial nucleation sites of 300 μm (type 3) and 500 μm (type 5) were used. The experimental results indicate a strong dependence of the occurrence of bubble coalescence on pressure. For the type 5 heater, a Gaussian distribution for the coalescence frequency when plotted over pressure is observed. Experimental results with the type 3 heater show a similar distribution of the frequency with a shifted maximum. Further, it is shown that during bubble coalescence a small droplet can remain inside the bubble and enhance the heat transfer, which is attributed to an additional thin film region. The formation of this remaining droplet is sensitive to system pressure. Numerical investigations of bubble coalescence were conducted with the computational fluid dynamics (CFD) software OpenFOAM. In OpenFOAM, dynamic mesh handling allows high spatial resolution at the phase boundary, which is captured with the volume-of fluid method. Evaporation and a subgrid microscale model were implemented in the flow solver to account for evaporation at the phase boundary and the three-phase contact line. The results show a strong dependence of bubble dynamics and coalescence on contact angle and bubble growth rate. Although it was possible to observe the creation of the residual droplet, more effort needs to be put into finding appropriate initial conditions.     

Visualization of Effects of Ultrasound on Liquid Droplet Solidification and Frost Formation on Cold Flat Surface

An experimental study was conducted to study the effect of ultrasonic vibrations on frost suppression on a cold flat surface in atmospheric air flow. A microscopic visualization on the liquid droplet solidification and frost formation process with and without the effect of 20-kHz ultrasound was made. The water droplets solidification and frost crystal growth on the solidified water droplet surface were comparatively observed. Meanwhile, the frost thickness variations were comparatively analyzed. It was found that almost no difference can be seen between the water droplet solidification onset time with the effect of ultrasound and that without the effect of ultrasound. However, after the water droplet solidifies, almost no growth of the frost crystal can be observed on the solidified water droplets surface with the effect of ultrasound. In addition, during the whole frost formation progress, very small growth of the frost layer can be seen on the flat surface with the effect of ultrasound. The experimental results showed that the frost growth process on the cold flat surface can be significantly restrained due to the effect of ultrasound.