裂缝性凝析气藏试井解释新方法

通过分析凝析气藏的相图,建立了凝析液饱和度随压力降的变化规律,并回归得出了相应的公式;同时通过对气体压缩因子、黏度随压力、温度的变化,建立了这些参数和无因次压力的关系;在双重介质地层假设的基础上,建立了在试井过程中凝析气相对渗透率随凝析液饱和度变化的凝析气藏试井解释数学模型,采用隐式迭代的方法进行了求解并进行了参数敏感性分析;结果表明:凝析液的饱和度对凝析气藏试井的压力及压力导数曲线有着很大的影响,早期由于凝析液的析出,阻碍了气藏的流动,导致压力及压力导数曲线上升;在凝析液饱和度达到峰值之后,随着凝析液的挥发,凝析气的相对渗透率逐渐恢复,压力及压力导数曲线又回归到正常的径向流位置;由于裂缝和基岩之间的压力差,使得裂缝弹性储容比在测试过程中发生变化,进而影响了压力及压力导数;窜流系数和裂缝弹性储容比的变化决定了窜流段发生的早晚和程度;而基岩中气体黏度的变化使得窜流的发生稍微滞后。     

基于多段压裂的页岩气藏不稳定压力分析

页岩气藏是一种具有吸附解吸作用过程,且储层物性为特低孔渗性的特殊气藏,国内外很多学者从不同的角度出发,对页岩气渗流规律展开了研究,得到了较符合页岩气藏渗流规律的成果。通过考虑页岩气藏的纳米级孔隙特征,页岩气的吸附解吸、扩散渗流特征,结合多段压裂水平井的流体渗流模型,建立了一个新的更适用于页岩气藏的多段压裂水平井的渗流数学模型。通过引入表观渗透率函数、点源函数理论、叠加原理,Laplace变换和Stehfest数值反演等数学方法 ,得到页岩气藏多段压裂水平井井底压力的连续点源解,绘制不同条件下的压力动态曲线,将储层中流体的渗流阶段分为6个阶段,并对相关参数进行了敏感性分析,得出吸附指数、窜流系数和弹性储容比在吸附解吸阶段影响明显。将该渗流数学模型应用于国内某页岩气藏压裂水平井,模型拟合参数和实际储层测井参数误差在3%~5%,说明该模型可为页岩气藏的不稳定产能预测和评价提供理论依据。     

三重介质页岩气藏分形渗流特征

页岩气藏开发中基质、天然微裂缝、人工裂缝同时参与渗流,且其内部还存在着吸附、解吸与滑脱特性,渗流机理复杂,分形理论对复杂系统恰好能比较精确地描述,因此本文引入分形理论,分别运用分形迂曲毛束管模型、分形面缝二叉树模型、分形面缝三叉树模型推导出基质、天然微裂缝、人工裂缝的分形孔隙度及分形表观渗透率,建立分形三重介质页岩气藏数学模型,绘制拟稳态与非稳态下的压力及压力导数响应曲线,划分渗流阶段。结果表明,分形因素影响渗流总径向流阶段,由于分形特征的影响,总径向流阶段压力导数曲线上翘;拟稳态窜流可分为早期纯井筒储集、天然裂缝与人工裂缝窜流、裂缝线性流、基质-天然裂缝窜流及总体径向流5个渗流阶段,非稳态窜流可分为早期纯井筒储集、过渡段、非稳态窜流段、系统线性流段及总径向流5个渗流阶段。     

非牛顿流体的非定常雷诺方程在动载径向滑动轴承中的应用

本文采用对遵从幂律的非牛顿流体近似分析方法,推导了非定常流动幂律流体雷诺方程的修正形式,并采用数值计算方法求取有限长轴承的幂律流体雷诺方程的数值解。计算表明非牛顿流体的特性对油膜压力的分布、承载力、以及动载轴承的轴心轨迹有相当的影响。     

幂律流体饱和多孔介质通道中的粘性耗散效应

针对Darcy-Brinkman-Forchheimer流动模型,分析了幂律型非牛顿流体在填充多孔介质平板通道中强迫对流传热过程充分发展的黏性耗散效应,并比较了三个不同的黏性耗散项Darcy项、Al-Hadhrami项和Forchheimer项对流动传热率的影响。推导出了无量纲轴向流速分布和无量纲温度分布的计算表达式,并在恒热流边界条件下,利用经典Runge-Kutta法进行数值求解。模拟结果表明,布林克曼数Br、达西数Da、综合惯性参数F和幂律指数n等重要参数对无量纲温度分布有着较大的影响,同时发现不同的黏性耗散效应对流动传热特性也有着重要的影响。     

幂律流体饱和多孔介质通道中的黏性耗散效应

针对Darcy-Brinkman-Forchheimer流动模型,分析了幂律型非牛顿流体在填充多孔介质平板通道中强迫对流传热过程充分发展的黏性耗散效应,并比较了三个不同的黏性耗散项Darcy项、Al-Hadhrami项和Forchheimer项对流动传热率的影响。推导出了无量纲轴向流速分布和无量纲温度分布的计算表达式,并在恒热流边界条件下,利用经典Runge-Kutta法进行数值求解。模拟结果表明,布林克曼数Br、达西数Da、综合惯性参数F和幂律指数n等重要参数对无量纲温度分布有着较大的影响,同时发现不同的黏性耗散效应对流动传热特性也有着重要的影响。     

计入非牛顿效应的曲轴轴承的混合润滑分析

分析了剪切变薄的非牛顿流变学特性和两表面都具有的纵向、横向和各向同性粗糙度对动载有限宽径向滑动轴承性能的综合影响。 Ｃｈｒｉｓｔｅｎｓｅｎ 的粗糙表面流体动力润滑的随机模型和 Ｇｒｅｅｎｗ ｏｏｄ Ｔｒｉｐｐ 接触压力的计算模型用于处理粗糙问题,并考虑了磨合对粗糙高度分布的影响。幂律流体模型用来表征剪切变薄的流变学特征,质量守恒的油膜破裂算法用于雷诺方程的求解。计算结果表明,粗糙度总是减小最小名义油膜厚度,并使油膜压力在接触区剧烈振荡,其幅值大于光滑表面时周期内的最大名义油膜压力。名义最小油膜厚度在纵向粗糙时最大,横向粗糙时最小。粗糙纹理相同时,相同粗糙结构下的名义最小油膜厚度在牛顿流体时大于不同粗糙结构时的相应值,在非牛顿流体情况下,结论相反。混合润滑的轴承性能受粗糙纹理和结构、幂律指数、轴承几何结构、轴颈质量及运行工况的综合影响。     

非牛顿流体液滴铺展过程的格子Boltzmann模拟北大核心CSCD

格子Boltzmann可有效模拟气液两相流动,成功应用于牛顿流体动态湿润领域和非牛顿流体单相流动领域的研究。将牛顿流体的两相流动格子Boltzmann模型与非牛顿流体单相流动格子Boltzmann模型相结合,建立了幂指流体两相流动格子Boltzmann模型,模拟了牛顿流体和幂指流体液滴铺展过程,并将液滴半径随时间的变化规律模拟结果与液滴铺展理论模型进行了比较,对两类流体的铺展指数与流变指数变化关系进行了分析讨论。     

颗粒堆积多孔介质内幂律流体流动阻力模型

基于平均水力半径理论、Carman-Kozeny-Blake模型及孔喉通道模型,综合考虑边壁摩擦和边壁空隙对压力降的影响,得到了关于迂曲度、孔隙率、喉孔比、颗粒直径、边壁修正系数及幂律指数等重要参数修正的阻力计算模型。结果表明:新模型在较大流态区间内的阻力预测值与文献吻合较好,证实了边壁对惯性项压力损失的影响与雷诺数和通道颗粒比值D/d的大小密切相关,同时推导出了幂律流体的临界雷诺数、修正渗透率及惯性系数的表达式。     

低催化剂载量直接甲醇燃料电池性能实验研究

利用自行设计的直接甲醇燃料电池实验系统研究了电池温度、阴极侧压力、甲醇溶液浓度和流量、氧气流量对低催化剂载量（阳极Pt-Ru载量为0．4mg／cm^2；阴极Pt载量为0．4mg／cm^2）直接甲醇燃料电池性能的影响。重点分析了运行参数对电池内部传质的影响。实验结果表明提高甲醇溶液浓度和流量不仅会强化甲醇向阳极催化剂层的传递，也会加剧甲醇窜流。另外，还研究了电流变化时电池电压的动态响应，结果表明甲醇窜流对电池动态响应起关键作用。     

Pressure transient analysis for asymmetrically fractured wells in dual-permeability organic compound reservoir of hydrogen and carbon

In this paper, a comprehensive semi-analytical model was presented to investigate pressure transient behavior for asymmetrically fractured wells in organic compound reservoir of hydrogen and carbon with dual-permeability behavior. Stehfest inversion algorithm can be used to transform it back into time domain to obtain pressure solution. The presented solution was validated well with numerical solutions. Flow characteristics for asymmetrically fractured wells in dual-permeability organic compound reservoir of hydrogen and carbon were divided into five regime. The effects of some important parameters on dimensionless pressure and its derivative curves were analyzed in details, including inter-porosity flow coefficient from matrix to natural fractures λ, storage coefficient ω, fracture asymmetry factor θ and permeability ratio κ. The presented model can be used to predict production performance and do well test analysis in the development of dual-permeability organic compound reservoir of hydrogen and carbon.     

Pressure transient analysis for fluid flow through horizontal fractures in shallow organic compound reservoir of hydrogen and carbon

Pure hydrogen does not occur in large quantities in nature, and it is usually locked up in energy-rich organic compound. One of the challenges to sustain the usage of hydrogen energy is to produce sufficient energy-rich organic compound from the organic compound reservoir of hydrogen and carbon, which requires understanding the fluid flow behavior through such reservoir. The horizontal fractures can be created during the hydraulic fracturing process in shallow energy-rich organic compound reservoirs due to the geo-mechanical effect. However, it lacks of a comprehensive analytical model to describe the transient flow behavior through the horizontal fractures. In this paper, an analytical model for horizontal fractures in shallow organic compound reservoirs considering the effects of wellbore storage and skin factor with constant pressure, closed and infinite boundary conditions, are presented to investigate pressure transient behavior and flow characteristics. The analytical solution is derived in Laplace domain, which may require numerical inverse transform to obtain the solution real space. To obtain the explicit form in real space, the approximate solutions for early time, middle time and late time are also presented to investigate the characteristics of type curves. Type curves are established for the transient pressure analysis to recognize the flow characteristics through horizontal fractures. Flow for horizontal fractures can be divided into five stages according to characteristics of dimensionless pseudo pressure derivative curve. The effects of parameters on pressure behavior are discussed in detail, which include wellbore storage coefficient, dimensionless formation thickness, dimensionless vertical location, and skin factor. The results indicate that horizontal fractures are more applicable in thin instead of thick reservoirs.     

泡沫铝通道内瞬态流动的平均换热系数

针对泡沫铝金属填充矩形通道内的对流换热开展了瞬态实验研究,分析了泡沫铝孔径(孔隙率)、流体流量(流速)等关键参数的影响。为了有效地处理实验数据,重新定义并推导了平均换热系数的计算公式,得到了泡沫铝通道内流动的平均换热系数,并引入了基于渗透率的雷诺数和达西数,确定了相关换热、流动准则数关系。实验研究表明,流速的增大有利于对流换热的强化:而平均换热系数对泡沫金属孔径较敏感;对于低孔隙率泡沫金属,渗透率成为影响换热强度的主要因素,相同或接近的孔隙率下,孔径越大,渗透率和达西数越大,越有利于换热,且压损减小。     

Transient free convection of a second-grade fluid flowing in a vertical cylinder

The intention of the present article is to examine the transient effect on the free convection of the second-grade fluid flowing in a vertical cylinder. We have found the analytical solution of the derived governing partial differential equations in nondimensional form corresponding to the velocity as well as the temperature fields by applying the Laplace transformation method in terms of the Bessel function of the first kind. To obtain the impacts of the appropriate parameters related to the given equations, such as the second-grade fluid parameter and the Prandtl number, the numerical values of the velocity are discussed and displayed in graphs. Furthermore, the mass flow rate and the skin friction at the inner surface of the cylinder are given in a tabular form. The influence of the second-grade fluid parameter is to decelerate the velocity as well as the mass flow rate and to enhance the steady-state time.     

相变换热适时动态过程数值模拟

以冷凝器为例，建立了分区和分流型的适时动态分布参数模型，模型建立过程中考虑流体的适时物性参数、湿区含液量、流动压力损失以及管壁蓄热等细节，使模型的准确性和通用性显著提高。在模拟过程中，计算机根据制冷剂状态自动由所建立的物性数据库中查取对应物性参数。模型采用显式方程组，求解速度快。由该模型可进行冷凝换热过程非稳态性能研究，获得换热过程冷、热流体温度、压力和冷凝状态等随时间变化的过程。通过实验验证表明，所建立的模型具有较高的准确性。     

Transient MHD convective flow of a micropolar fluid past a moving vertical plate in the presence of thermal diffusion

In this article, we investigate a transient magnetohydrodynamic convective micropolar fluid flow over a semi-infinite vertical plate embedded in a porous medium in the presence of chemical reaction and thermal diffusion. The dimensionless governing equations are solved by adopting the regular perturbation technique. The impact of various parameters on the velocity, microrotation, temperature, concentration profiles, skin friction, Sherwood number, and Nusselt number over the boundary layer is analyzed using graphs. The fluid velocity and microrotation reduce under the effect of thermal diffusion and chemical reaction. Furthermore, concentration rises due to thermal diffusion (Soret) effect, but concentration falls under the effect of chemical reaction. It is found that the velocity and skin friction fall with enhancing value of magnetic parameter. But Sherwood number increases as the magnetic parameter increase.     

含引水和尾水明渠输水的水电站过渡过程分析

鉴于无压明渠的水力特性直接影响含明渠引水式水电站的过渡过程和运行控制,结合有压输水系统的特征线法,采用明渠瞬变流分析的特征隐式格式和相应的边界条件,构建含非自动调节引水明渠、压力前池、尾水池和尾水明渠的引水式水电站的过渡过程分析模型,研究了明渠流水力特性对水电站过渡过程和稳定性的影响。结果表明,在大波动过渡过程中,明渠流水力特性对机组蜗壳进口内水压力和转速极值的影响很小,而尾水渠水力特性及尾水池最低涌波水位决定了尾水管进口的最小内水压力;考虑明渠瞬变流特性的影响,水力干扰下受扰机组的调节品质变化较为明显,而水力-机械系统小波动调节品质变化较小。     

考虑动态摩阻的管道内水气耦合瞬变流的数值模拟

输水管道系统中经常会发生水气耦合瞬变流,可能会引起异常压力波动,甚至造成爆管事故。目前针对水气耦合瞬变流的研究很少考虑动态摩阻的影响,往往会低估瞬变过程能量衰减。对此,引入一种高效准确的简化加权类动态摩阻模型,建立考虑动态摩阻的水气耦合瞬变流模型。同时,采用虚拟塞法避免了特征线法在水气交界面的动态追踪时数值插值和求解的复杂。对比分析该模型计算结果与不考虑动态摩阻模型计算结果、试验数据,发现考虑动态摩阻的模型能更好地预测气团压力衰减和耗散,与试验压力峰值更为接近;入口压力越大,初始气团越小,动态摩阻对压力波动衰减的影响越大。     

Transient computation fluid dynamics modeling of a single proton exchange membrane fuel cell with serpentine channel

The proton exchange membrane fuel cell (PEMFC) has become a promising candidate for the power source of electrical vehicles because of its low pollution, low noise and especially fast startup and transient responses at low temperatures. A transient, three-dimensional, non-isothermal and single-phase mathematical model based on computation fluid dynamics has been developed to describe the transient process and the dynamic characteristics of a PEMFC with a serpentine fluid channel. The effects of water phase change and heat transfer, as well as electrochemical kinetics and multicomponent transport on the cell performance are taken into account simultaneously in this comprehensive model. The developed model was employed to simulate a single laboratory-scale PEMFC with an electrode area about 20 cm². The dynamic behavior of the characteristic parameters such as reactant concentration, pressure loss, temperature on the membrane surface of cathode side and current density during start-up process were computed and are discussed in detail. Furthermore, transient responses of the fuel cell characteristics during step changes and sinusoidal changes in the stoichiometric flow ratio of the cathode inlet stream, cathode inlet stream humidity and cell voltage are also studied and analyzed and interesting undershoot/overshoot behavior of some variables was found. It was also found that the startup and transient response time of a PEM fuel cell is of the order of a second, which is similar to the simulation results predicted by most models. The result is an important guide for the optimization of PEMFC designs and dynamic operation.