Numerical Investigation into the Development Performance of Gas Hydrate by Depressurization Based on Heat Transfer and Entropy Generation Analyses

The purpose of this study is to analyze the dynamic properties of gas hydrate development from a large hydrate simulator through numerical simulation. A mathematical model of heat transfer and entropy production of methane hydrate dissociation by depressurization has been established, and the change behaviors of various heat flows and entropy generations have been evaluated. Simulation results show that most of the heat supplied from outside is assimilated by methane hydrate. The energy loss caused by the fluid production is insignificant in comparison to the heat assimilation of the hydrate reservoir. The entropy generation of gas hydrate can be considered as the entropy flow from the ambient environment to the hydrate particles, and it is favorable from the perspective of efficient hydrate exploitation. On the contrary, the undesirable entropy generations of water, gas and quartz sand are induced by the irreversible heat conduction and thermal convection under notable temperature gradient in the deposit. Although lower production pressure will lead to larger entropy production of the whole system, the irreversible energy loss is always extremely limited when compared with the amount of thermal energy utilized by methane hydrate. The production pressure should be set as low as possible for the purpose of enhancing exploitation efficiency, as the entropy production rate is not sensitive to the energy recovery rate under depressurization.     

水流动强化天然气水合物降压分解研究

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。     

水合物藏降压开采实验及数值模拟

建立了降压法开采水合物藏数学模型,考虑了气-水-水合物-冰相多相渗流、水合物相变及分解动力学过程、冰-水相变、热传导、对流过程、渗透率变化等对于水合物分解的影响。三维水合物藏模拟表明:在开采前期阶段,可采用降压法,但随着储层能量消耗,产气速度下降很快,需转变开采方式。分析了一些主要参数,如孔隙度、渗透率、饱和度、压力等对水合物开采的影响。     

Formation and dissociation of gas hydrate inclusions during migration in water

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.     

热力法开采地层天然气水合物的热动力评价

本文在推导热力作用下水合物地层温度分布基础上,发展了评价热力法开采天然气水合物的热效率(用于水合物分解的热量与输入总的热量之比)和能量效率(即输出能量与输入能量之比)的模型.模型分析表明,水合物地层热物性参数以及水合物饱和度决定了热力法开采的能量效率.在注入蒸汽开采初始条件下,能量效率可以达到7.0.     

产水气井井筒温度压力计算方法

应用考虑气液相间滑脱与流体沿井筒截面非均匀分布的漂移模型,结合动量守恒、能量守恒和井筒传热学,建立考虑井斜变化的气井井筒温度、压力耦合预测模型,通过15口实测井数据对模型进行验证.结果表明:所建模型可以准确计算产水气井井筒的温度和压力,计算结果平均绝对误差3.60%,满足工程计算要求.     

Methane combustion in hydrate systems: Water-methane and water-methane-isopropanol

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.     

空调器焓差实验室节能的实验研究

在焓差实验室的室内侧增加一个热回收装置,利用高温高压制冷剂气体对空气经行加热,减少电加热及电加湿;室外侧采用热气旁通,使蒸发温度控制在一个合适的范围内,减少加湿量,达到节能目的。     

深层高温高压气井临界产量计算模型

基于热膨胀效应和环空体积变化效应这两种环空带压机理,结合气井生产过程中井筒温度-压力分布计算方法,考虑油层套管和油管的许可压力值,建立一个深层高温高压气井临界产量计算模型.运用迭代法求解模型,编制相关程序.结果表明:环空压力与主要受温度的影响,气井产量越高,井口温度越高,环空压力越大,油套管安全系数越低,因此需要考虑管柱安全性确定临界流量.利用新疆某深层高温高压气井的实际数据进行实例计算,结果可为深层高温高压气井的合理配产提供依据.     

On hydrate growth in aquatic gas solution

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.     

Inward transport and compression of a positron plasma by a rotating electric field

Inward transport of a magnetized pure positron plasma confined in a Penning-Malmberg trap is produced by applying a rotating electric field to the plasma. Compression is observed over a broad range of frequencies. Compression factors up to 20 in central density were obtained. Positron collisions with a neutral buffer gas are used to counteract the heating due to the rotating electric field. The results have implications for a variety of applications including the production of brightness enhanced positron beams, the study of electron-positron plasmas, and antihydrogen production.     

裂缝性油藏水平井产能计算方法

根据裂缝性油藏水平井渗流特征,将渗流区域等效为近井区域和远井区域.远井区域视为连续均匀介质.在近井区域,基于势叠加、镜像反映原理和微元线汇思想,建立考虑天然裂缝和水平井生产段共同渗流的耦合模型.组合两个流动区域得到裂缝性油藏水平井产能评价模型,并进行求解.实例计算结果表明,由于考虑了裂缝之间的干扰,用建立的模型计算的水平井产能小于用理论公式计算的水平井的产能,与实际产能比较接近;随着裂缝密度增加,产量逐渐增加,但增加的幅度降低.     

静止水滴生成气体水合物的动力学研究

作为喷雾强化方式制备气体水合物的初步研究,本文通过研究静止水滴形成气体水合物过程的传热传质机理,建立气体水合物的生成动力学模型。研究结果表明强化气相与水合物颗粒之间的接触传热对提高水合物的生成速率具有十分重要意义。     

Modelling of decomposition of a single gas hydrate particle in water behind the shock wave front

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.     

Modeling the Water Droplet Evaporation Processes with Regard to Convection,Conduction and Thermal Radiation

A predictive model was developed for investigation of high-temperature heating and evaporation of water droplets. The model takes into account the basic interrelated processes of heat transfer and phase transitions. Typical velocity and temperature profiles were found in the high-temperature gas–water droplet system with external gas medium temperature varied from 100 to 800°C. Various formulations of the problem, significantly different in the type of considered processes and factors, are considered.We analyzed temperature conditions of heating and evaporation of water droplets, which allow the use of simplified models and which need consideration of all complex interrelated processes of heat and mass transfer (including convection, conduction and radiant heat transfer in droplets, and also in the surface vapor–gas layer).     

Spiral phase-change material for enhancing natural circulation solar water heater: An experimental study

This article studies the use of spiral phase-change material as an energy storage to improve the performance of a domestic solar water heater. The heating and cooling tests have been conducted for the vertical and horizontal position of the phase-change material in the water heater tank. The vertical position phase-change material yields better results than horizontal position. The charging energy and system thermal efficiencies of the tank are increased up to 20% and 12%, respectively, when the phase-change material is kept vertically. Also, it is observed that better heat transfer coefficient between water and phase-change material and upgraded thermal stratification during the cooling tests.     

高超声速飞行器前缘疏导式热防护结构的实验研究

针对高超声速飞行器前缘疏导式防热结构的特点,设计前缘内嵌高导热率材料结构和一体化层板热管结构两类对比实验,用于验证前缘疏导式防热结构的可行性.利用球形短弧氙灯作为辐射热源模拟气动加热,分别对钢质前缘、内嵌铜材料的钢质前缘和一体化层板式热管前缘进行加热,测量前缘驻点区域和尾部翼面区域的温度变化.实验结果表明:内嵌高导热率材料的前缘疏导结构能够降低头部驻点区的温度,提高尾部低温区的温度,实现对前缘结构的热防护;以蒸馏水作为工质一体化层板式热管前缘结构,在较低热流条件下也能够实现对前缘驻点区的疏导式热防护,但在较高热流条件下,由于水蒸气压力过大使得层板式前缘结构发生破坏,体现出热管内部工作介质对结构防热效果和应用范围都起到的关键作用.     

用分子动力学模拟甲烷水合物热激法结合化学试剂法分解

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.     

Water vapor desorption and adsorbent regeneration for air conditioning unit using pulsed corona plasma

The dehumidifying action of a dehumidifier or air conditioner was employed to achieve a comfortable and desirable indoor comfort. Water vapor adsorbed on an adsorbent substance needs to be regenerated when the water vapor exceeds the adsorption capacity. The conventional process for adsorbent regeneration or moisture desorption uses the heat by means of the electric heater. In the present study, the water vapor desorption from the adsorbent material was investigated using a pulsed corona plasma for possible replacement of the electric heater. The water vapor desorption for a given power (defined as desorption efficiency) using the pulsed corona plasma was found to be superior over conventional thermal desorption. The gradient of desorption (desorption rate) was found to be significantly higher for plasma desorption, so that faster desorption can be achieved without excessive gas heating. In addition, the plasma desorption was not affected by the initial moisture content in an indoor environment, which leads to more economical, controllable, and flexible air conditioning system.     

Experimental Study of Two Phase Closed Thermosyphon Using Cuo/Water Nanofluid in the Presence Of Electric Field

In this article, the effect of applying an electric field on the performance of a two-phase closed thermosyphon is investigated experimentally. A CuO/water nanofluid is used as the working fluid in the present investigation; 40% of the evaporator volume is filled with the working fluid during the tests. An electric field in various voltages ranging from 5 to 20 kV is applied to the system. Also, the input power supplied to the evaporator varies between 60 to 120 W. The thermal efficiency and the thermal resistance of the two-phase closed thermosyphon are evaluated in various strengths of electric field and different volume fractions. It is found that using the nanofluid and applying an electric field could increase the thermal efficiency by up to 30% as compared with the case in which the working media is pure water and no electric field is applied. To illustrate the effect of the electric field on the heat transfer enhancement, the augmentation Nusselt number, defined as the ratio of the Nusselt numbers after and before applying the electric field, is discussed. The results show that utilizing an electric field is more advantageous when the input power applied to the system is lower.