VES—CO2清洁泡沫压裂液携砂性能实验研究

在大型高压泡沫压裂液实验回路上,对VES—C02清洁泡沫压裂液的携砂性能进行了实验研究。分析了携砂泡沫压裂液流动时临界沉降速度的产生原因,并根据实验结果分析了温度、泡沫质量及支撑剂浓度对临界沉降流速的影响。临界沉降流速随温度的升高而增大,随泡沫质量和支撑剂体积浓度的增大而减小,研究发现当支撑剂浓度大于0．25时,开始出...     

改良干法压裂液摩擦阻力特性实验研究

对改良的干法压裂液这种非牛顿流体的摩擦阻力特性的正确认识,关系着干法压裂技术的有效实施.为此,本文在大型高压泡沫压裂液实验回路上,考察了在模拟实际施工条件下的改良干法压裂的摩擦阻力特性.实验表明:改良后的干法压裂液摩擦阻力系数随压力、温度的升高和泡沫质量的增加而增大,随流速的增加而减小.在实验范围内,温度对摩擦阻力系数的影响不大.实验得到了改良的干法压裂液摩擦阻力系数与广义雷诺数的关联式,平均计算误差为9.19%.     

竖管中CO2泡沫压裂液的管流阻力特性

CO2泡沫压裂液具有非牛顿流体性质,其在实际施工条件下的油管流动特性直接影响到对井底射孔处的压力确定,从而对进行准确的裂缝预测、压裂效果评估具有重要的意义。对垂直下降管中CO2泡沫压裂液的管流阻力特性进行了实验研究,二氧化碳泡沫压裂液的摩擦阻力随着流速的增大而增大,随着温度和压力的增大而减小;并通过实验研究得出了泡沫压裂液在垂直下降管中流动时的摩擦阻力系数的计算关联式,其在本文实验工况下的平均计算误差为14.8％。     

压裂液返排冲刷支撑剂颗粒的DEM-CFD模拟研究

支撑剂回流是压裂液返排过程中重点问题之一。目前普遍认为压裂液返排流速对于支撑剂颗粒堆的稳定性具有重要影响,并有研究明确了压裂液返排的临界流速条件。本文通过计算流体力学和离散颗粒元(CFD-DEM)的耦合仿真,对目前已有的支撑剂回流临界返排流速计算模型进行验证,研究了支撑剂颗粒参数(粒径和密度)和流道次缝对于临界返排流速的影响并揭示了相应的流动机理。研究结果可为优化压裂液返排流程提供理论指导。     

亚临界压力区垂直上升管内传热特性实验研究

本文开展了亚临界压力下垂直上升内螺纹管中水的传热特性的实验研究,并与对应条件下光管内水的传热特性进行了对比、分析.结果发现:内螺纹管和光管中两相饱和流动沸腾换热随热流密度的增加或压力的升高而增大,基本不随质量流速的变化而变化;相同工况下内螺纹管的饱和沸腾换热系数大约为光管的1.1～1.2倍。内螺纹管和光管的过冷沸腾起始干度都随质量流速的减小或者压力的升高或者热流密度的增大而增大;在相同工况下本文实验内螺纹管中的过冷沸腾起始干度比光管中的要小至少0.2。光管中主要发生偏离核态沸腾(DNB),临界干度随热流密度的减小或质量流速的增加或压力的降低而增大;内螺纹管中主要发生烧干,运行参数对临界干度的影响不大。     

液滴在管间气流作用下的偏移特性

为研究蒸发器内液滴的偏移特性,采用理论分析和实验参数结合的方法推导新的关系式。计算了不同液滴直径或喷淋密度下,对应不同蒸汽流速时液滴液柱的偏移距离。给出了不同工况下能保证液滴下落到下一根管上的临界蒸汽流速。计算结果表明觉随蒸汽流速的增大,偏移距离逐渐增加;临界流速随液滴直径的增大而增加,但其随饱和温度的升高而降低。     

多孔细径微肋管内CO2流动蒸发换热特性的研究

对亚临界二氧化碳在带有微肋的微细通道内的蒸发换热特性进行了实验研究.实验段为长0.6 m,内径1.7 mm的八孔带0.16 mm高微肋的铝制扁管.实验中参数的变化为:蒸发温度1～15 ℃,质量流速100～300 kg/m2s,热流密度1.67～8.33 kW/m2,干度0.1～0.9.实验结果表明,二氧化碳在带有微肋的微细通道中的蒸发换热系数高于其在光滑微细通道内的换热.二氧化碳的流动蒸发换热系数主要受热流密度和蒸发温度的影响,基本上是换热系数随热流密度及蒸发温度的增加而增加,但同时临界干度前移及滞后,而质量流速对换热系数的影响较弱;压力损失随质量流速和热流密度的增加以及蒸发温度的降低而增加.     

砂粒与复杂流体压裂液在裂缝中的流动特性研究

在矩形裂缝通道中,应用高速摄像技术,研究了复杂流体压裂液水平流动过程中砂粒的沉降速度,测试了复杂流体的流变学特性,分析了复杂流体的水平流动如何影响砂粒的沉降.研究结果表明,流性指数不等于1的复杂流体,其水平流速影响砂粒的沉降规律,砂粒在裂缝中水平流动过程的沉降速度不仅随复杂流体表观粘度的减小而增大,同时随复杂流体水平流速的增大而增大,是静止沉降速度的数倍至十数倍.     

水–酒精混合工质Marangoni凝结液珠表面温度随液珠尺寸变化研究

基于红外测温技术,开展了水平表面水–酒精混合工质Marangoni凝结实验,研究了液珠表面温度随液珠尺寸的变化规律,分析了射流水温、酒精蒸气质量浓度及蒸气压力等因素的影响。研究发现:液珠表面平均温度随液珠半径的增大而增大,并且同一工况下具有良好的相关性。当射流水温升高时,液珠表面温度分布曲线朝着更小半径和更高温度方向移动。当酒精蒸气质量浓度从0.5%增大到10%时,液珠表面平均温度整体下降约4.5℃。随着蒸气压力增大,表面温度分布向着更高温度及更大半径方向发展。     

超临界CO2-DME混合物竖直圆管内传热特性数值研究

本文采用RNG k-ε湍流模型对超临界CO₂/DME(二甲醚)二元混合工质在竖直圆管内的传热特性进行了数值模拟研究。管径4 mm,管长为1000 mm;CO₂/DME浓度配比分别为97/3、95/5、92/8、90/10、85/15、以及70/30;质量流速为125~200 kg·m^-2.s^-1;热流密度为15~30 kW.m^-2,入口温度295~308 K,入口压力8~15 MPa。不同浓度配比的混合工质在各自临界压力下应用时,随着DME浓度的增加,换热系数的峰值逐渐减低,但在温度大于310 K时混合工质的换热系数会高于纯CO₂。压力相同时,随着DME浓度的增大,拟临界温度升高,换热系数峰值点也随之向温度升高的方向移动。混合工质的换热系数随质量流速的增大而增大。在拟临界点前,增大热流密度及降低压力对管内传热有利,而在拟临界点之后,换热系数随热流密度的升高以及压力的降低而降低。     

Separation efficiency and pressure drop of SiC ceramic and Mellapak structured packings

This paper describes application of SiC ceramic foam to distillation. The investigated foam SiC ceramic packing and smooth SiC ceramic packing parameters in geometrical characteristics are similar to the Mellapale structured packing parameters. The hydrodynamic performance parameters including pressure drop for dry and wet packing, flood velocity, and liquid hold-up, which are determined in a plexiglas tower of a 100-mm internal diameter. The mass transfer efficiency is measured in another glass tower of a 100-mm internal diameter by total reflux experiments, using a mixture of n-heptane and cyclohexane at atmospheric pressure. The experimental results show that the foam SiC ceramic structured packing has a higher dry and wet pressure drop, higher liquid hold-up, higher mass transfer efficiency, and unchanged flood velocity, comparing with a smooth SiC ceramic structured packing with the same shape. Comparison of the experimental data on the separation efficiency and relative pressure drop was performed for foam/smooth SiC ceramic and metal Mellapak structured packings.     

矩形管内临界爆轰动力学数值分析

 对矩形管内临界爆轰动力学特征进行了数值分析。采用基元反应描述爆轰化学反应过程,采用二阶附加半隐的龙格-库塔法和5阶WENO格式求解二维反应欧拉方程。对于25%氩稀释化学计量比的氢氧预混气体,当管道宽度为30 mm、初温为300 K时,产生临界爆轰的预混气体初压为3.5 kPa。在此临界条件下,获得了临界爆轰胞格结构、沿壁面的速度和峰值压力曲线及流场波系演变特征。着重对比分析了矩形管内临界爆轰与普通爆轰在爆轰波速度、平均速度、胞格宽长比、横波结构、未反应气囊及旋涡结构之间的差异,深入认识了临界爆轰的不稳定性和化学反应动力学特征。     

Detonation of explosive Proppant: RDX-containing water-saturated sand

The results of experimental investigations and thermodynamic calculations of the detonation of explosive proppant, an RDX-containing water-saturating sand, are reported. The material studied is of interest for use as an explosive additive to propping material injected into hydraulic fractures of oil-bearing beds. The tests were conducted in duralumin casings with cylindrical or planar inner channels. The dependences of the detonation velocity on the RDX content in the mixture in the range of 14 to 74 wt %, RDX and sand particle size, and initial temperature are examined. The critical detonation diameter of the charge decreases with increasing content RDX in the mixture, being only several millimeters at RDX contents of 30 wt % and above. Polydisperse RDX provides a high detonability of such mixtures; use of narrow particle size RDX fractions, especially coarse (0.4–0.7 mm), significantly increases the critical detonation diameter. As the initial temperature of the mixture is increased from 20 to 90°C, the critical detonation width decreases severalfold. The detonation of mixtures in a convergent planar channel occurs at a constant rate, which differs little from the detonation velocity measured in a cylindrical channel. Reaching the place where the opening of the channel is less than the critical width, detonation fails abruptly. Thermodynamic calculations of the detonation characteristics of the explosive proppant are performed using the BKWS equation of state under the assumption that the sand component behaves as an inert additive, being in mechanical equilibrium with the detonation products of the RDX-water mixture. A satisfactory agreement with the experimental data on the detonation velocity and its dependence on the RDX content is demonstrated. This makes it possible to conclude that RDX mixed with water-saturated sand detonates within a narrow reaction zone without significant convective heat transfer to the inert additive.     

Filamentation Instability in a Current‐Carrying Plasma in the Presence of Quantum Effects

The filamentation instability of a current‐carrying plasma under the diffusion condition is investigated taking into account the Bohm potential and the Fermi electron pressure. Using quantum hydrodynamic equations, the dispersion relation and growth rate of the instability is obtained. It is found that the filamentation instability, in the presence of quantum effects, depends on various characteristic parameters such as: electron Fermi velocity, plasma number density, ion thermal velocity and electron drift velocity. Moreover, the wavelength region in which the instability occurs is more restricted and the minimum size of filaments is larger, in comparison with the classical case. It is also found that the growth rate of the instability is smaller in the presence of quantum effects. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Wind noise measured at the ground surface

Measurements of the wind noise measured at the ground surface outdoors are analyzed using the mirror flow model of anisotropic turbulence by Kraichnan [J. Acoust. Soc. Am. 28(3), 378-390 (1956)]. Predictions of the resulting behavior of the turbulence spectrum with height are developed, as well as predictions of the turbulence-shear interaction pressure at the surface for different wind velocity profiles and microphone mounting geometries are developed. The theoretical results of the behavior of the velocity spectra with height are compared to measurements to demonstrate the applicability of the mirror flow model to outdoor turbulence. The use of a logarithmic wind velocity profile for analysis is tested using meteorological models for wind velocity profiles under different stability conditions. Next, calculations of the turbulence-shear interaction pressure are compared to flush microphone measurements at the surface and microphone measurements with a foam covering flush with the surface. The measurements underneath the thin layers of foam agree closely with the predictions, indicating that the turbulence-shear interaction pressure is the dominant source of wind noise at the surface. The flush microphones measurements are intermittently larger than the predictions which may indicate other contributions not accounted for by the turbulence-shear interaction pressure.     

垂直上升管泡状流压力波动的多尺度分析

从理想的单气泡运动物理模型和离散正交小波与统计相结合的信号处理技术研究了泡状流压力波动的机理与多尺度时频规律,得到以下结论:泡状流的压力波动主要来源于气泡的运动和诱导湍流及液相湍流,其中在低流速下前者产生的压力波动幅度大于后两者;存在一个临界频率,低于该频率压力信号均方根随频率的增加而增加,高于该频率压力信号均方根随频率的增加而减小;发生流型转变时压力信号的时频特征发生明显改变,最大均方根出现在更低的频率区。     

Influence of Vertical Foam Flow Liquid Drainage on Tube Bundle Heat Transfer Intensity

The results of an experimental investigation of staggered tube bundle heat transfer to upward and downward moving vertical foam flow are presented in this article. It was determined that a dependency exists between tube bundle heat transfer intensity on foam volumetric void fraction, foam flow velocity and direction, and liquid drainage from foam. In addition to this, the influence of tube position of the bundle on heat transfer was investigated. Experimental results were summarized by criterion equations, which can be applied in the design of foam type heat exchangers.     

Numerical simulations of two-dimensional foam by the immersed boundary method

In this paper, we present an immersed boundary (IB) method to simulate a dry foam, i.e., a foam in which most of the volume is attributed to its gas phase. Dry foam dynamics involves the interaction between a gas and a collection of thin liquid-film internal boundaries that partition the gas into discrete cells or bubbles. The liquid-film boundaries are flexible, contract under the influence of surface tension, and are permeable to the gas, which moves across them by diffusion at a rate proportional to the local pressure difference across the boundary. Such problems are conventionally studied by assuming that the pressure is uniform within each bubble. Here, we introduce instead an IB method that takes into account the non-equilibrium fluid mechanics of the gas. To model gas diffusion across the internal liquid-film boundaries, we allow normal slip between the boundary and the gas at a velocity proportional to the (normal) force generated by the boundary surface tension. We implement this method in the two-dimensional case, and test it by verifying the von Neumann relation, which governs the coarsening of a two-dimensional dry foam. The method is further validated by a convergence study, which confirms its first-order accuracy.     

Experimental characterization of novel SiC foam corrugated structured packing with varied pore size and corrugation angle

In our study, SiC foam material has been applied to produce corrugated structured packing in distillation. Three kinds of novel packing with different pore size and corrugation angle have been developed and tested in pilot scale, respectively, to investigate the influence of structural parameters on the performance of SiC foam corrugated structured packing. Hydraulic parameters including pressure drop for dry and wet packing and flooding velocity are determined in an organic glass tower of 600 mm internal diameter, using gas–water. Mass transfer efficiency (HETP) is measured by total reflux experiments in a column with a 310 mm diameter at atmospheric pressure, using a mixture of n-heptane and cyclohexane. The experimental results indicate that SFP-500YD3 with a smaller pore size has higher dry and wet pressure drop, lower flooding velocity and higher mass transfer efficiency compared with SFP-500Y-D5. SFP-500X-D3 with a 30° corrugation angle exhibits lowest pressure drop and highest separation efficiency among all three packings. This study reveals the influence of structural characteristics of SiC foam corrugated structured packing on its performance.