Preparation and stabilization mechanism of carbon dots nanofluids for drag reduction

During the development of low or ultra-low permeability oil resources,the alternative energy supply becomes a prominent issue.In recent years,carbon dots(CDs)have drawn much attention owing to their application potential in oil fields for reducing injection pressure and augmenting oil recovery.However,carbon dots characterized of small size,high surface energy are faced with several challenges,such as self-aggregation and settling.The preparation of stably dispersed carbon dots nanofluids is the key factor to guarantee its application performance in formation.In this work,we investigated the stability of hydrophilic carbon dots(HICDs)and hydrophobic carbon dots-Tween 80(HOCDs)nanofluids.The influences of carbon dots concentration,sorts and concentration of salt ions as well as temperature on the stability of CDs were studied.The results showed that HICDs are more sensitive to sort and concentration of salt ions,while HOCDs are more sensitive to temperature.In addition,the core flooding experiments demonstrated that the pressure reduction rate of HICDs and HOCDs nanofluids can be as high as 17.88%and 26.14%,respectively.Hence,the HICDs and HOCDs nanofluids show a good application potential in the reduction of injection pressure during the development of low and ultra-low permeability oil resources.

Experiment and mechanism of dynamic drag reduction in pipeline transportation

Based on the analysis of the disadvantages of traditional methods in reducing pipeline resistance, the new conception of dynamic drag reduction in pipeline transportation has been proposed. The experimental results and mechanism of dynamic reduction of pipeline resistance were also discussed in detail. The main conclusion is that the dynamic reduction of resistance exerts forces on the moving materials along both the radial direction and the axial direction. The radial force throws the materials upwards to depart from the pipe wall to reduce the frictional force, while the axial force directly reduces the resistance by providing the force to overcome the drag.

The Mechanism of Drag Reduction around Bodies of Revolution Using Bionic Non-Smooth Surfaces

Bionic non-smooth surfaces （BNSS） can reduce drag. Much attention has been paid to the mechanism of shear stress reduction by riblets. The mechanism of pressure force reduction by bionic non-smooth surfaces on bodies of revolution has not been well investigated. In this work CFD simulation has revealed the mechanism of drag reduction by BNSS, which may work in three ways. First, BNSS on bodies of revolution may lower the surface velocity of the medium, which prevents the sudden speed up of air on the cross section. So the bottom pressure of the model would not be disturbed sharply, resulting in less energy loss and drag reduction. Second, the magnitude of vorticity induced by the bionic model becomes smaller because, due to the sculpturing, the growth of tiny air bubbles is avoided. Thus the large moment of inertia induced by large air bubble is reduced. The reduction of the vorticity could reduce the dissipation of the eddy. So the pressure force could also be reduced. Third, the thickness of the momentum layer on the model becomes less which, according to the relationship between the drag coefficient and the momentum thickness, reduces drag.

Recent progress in research and design concepts for the characterization,testing,and photocatalysts for nitrogen reduction reaction

The reduction of molecular nitrogen(N_(2))to ammonia(NH_(3))under mild conditions is one of the most promising studies in the energy field due to the important role of NH_(3)in modern industry,production,and life.The photocatalytic reduction of N_(2)is expected to achieve clean and sustainable NH_(3)production by using clean solar energy.To date,the new photocatalysts for photocatalytic reduction of N_(2)to NH_(3)at room temperature and atmospheric pressure have not been fully developed.The major challenge is to achieve high light-absorption efficiency,conversion efficiency,and stability of photocatalysts.Herein,the methods for measuring produced NH_(3)are compared,and the problems related to possible NH_(3)pollution in photocatalytic systems are mentioned to provide accurate ideas for measuring photocatalytic efficiency.The recent progress of nitrogen reduction reaction(NRR)photocatalysts at ambient temperature and pressure is summarized by introducing charge transfer,migration,and separation in photocatalytic NRR,which provides a guidance for the selection of future photocatalyst.More importantly,we introduce the latest research strategies of photocatalysts in detail,which can guide the preparation and design of photocatalysts with high NRR activity.

Active control of turbulence for drag reduction based on the detection of near-wall streamwise vortices by wall information

The spatial relations between the measurable wall quantities （streamwise shear stress τwx, spanwise shear stress τwz, and pressure fluctuations Pw） and the near-wall streamwise vortices （NWSV） are investigated via direct numerical simulation （DNS） databases of fully developed turbulent channel flow at a low Reynolds number. In the stan- dard turbulent channel flow, the results show that all the wall measurable variables are closely associated with the NWSV. But after applying a stochastic interference, the relation based on τwx breaks down while the correlations based on Pw and τwz are still robust. Hence, two wall flow quantities based on Pw and τwz are proposed to detect the NWSV. As an appli- cation, two new control schemes are developed to suppress the near-wall vortical structures using the actuation of wall blowing/suction and obtain 16 % and 11% drag reduction, respectively.

Polymerization Mechanism of α-Linear Olefin

The density functional theory on the level of B3LYP/6-31G was empolyed to study the chain growth mechanism in polymerization process of α-linear olefin in TiCl3/AlEt2Cl catalytic system to synthesize drag reduction agent. Full parameter optimization without symmetry restrictions for reactants, products, the possible transition states, and intermediates was calculated. Vibration frequency was analyzed for all of stagnation points on the potential energy surface at the same theoretical level. The internal reaction coordinate was calculated from the transition states to reactants and products respectively. The results showed as flloes： （i） Coordination compounds were formed on the optimum configuration of TiCl3/AlEt2Cl.（ii） The transition states were formed. The energy di？erence between transition states and the coordination compounds was 40.687 kJ/mol. （iii） Double bond opened and Ti-C（4） bond fractured, and the polymerization was completed. The calculation results also showed that the chain growth mechanism did not essentially change with the increase of carbon atom number of α-linear olefin. From the relationship between polymerization activation energy and carbon atom number of the α-linear olefin, it can be seen that the α-linear olefin monomers with 6-10 carbon atoms had low activation energy and wide range. It was optimum to synthesize drag reduction agent by polymerization.

柔性表皮与鲨鱼体表粘液耦合作用减阻效果数值模拟

本文采用粘流数值模拟方法,通过Workbench搭建双向流固耦合求解器,对粘液析出的柔性平板减阻效果进行数值模拟研究。结果表明,耦合粘液析出与柔性覆盖层可进一步提升减阻效果。粘液与柔性平板耦合之后,起到了进一步减阻的作用。从减阻效果来说,粘液与柔性平板的减阻技术可行,能在粘液减阻基础上进一步减少16.3%~21.20%。

非常规油气开采压裂用减阻剂的研究现状及展望

为降低压裂施工摩阻,提高非常规储层的压裂改造效果,在系统调研国内外关于压裂用减阻剂文献的基础上,综述了减阻剂的类型和减阻机理,分析了减阻性能的影响因素,介绍了减阻剂的现场应用情况和减阻剂主要存在的问题,并提出了减阻剂未来的发展方向。结果表明:目前常用的减阻剂主要存在成本高、性能不稳定、减阻机理不明确的问题;低成本、对储层伤害低、减阻性能高效的多功能型纳米复合减阻剂将是未来减阻剂研究的重点和热点。通过对减阻剂的全面研究,可为目前减阻剂性能的提升、新型减阻剂的研发和非常规油气的开采提供可行性的帮助。

反刍动物甲烷排放测定方法及减排措施研究进展

甲烷(CH_(4))作为三大温室气体之一,占全球温室气体总量的15%。人类生产活动是CH_(4)排放的主要来源。畜牧业生产过程中反刍动物排放的CH_(4)约占人类农业生产的28%。由反刍动物瘤胃微生物发酵排放的CH_(4),不仅会导致饲粮能量的浪费(占饲粮总能的2%~12%),还会造成全球气候变暖。因此,降低反刍动物瘤胃内CH_(4)的生成和排放,对于减少饲粮能量损失和实现“双碳”目标均具有重要意义。本文通过对反刍动物瘤胃CH_(4)生成机理、测定方法及CH_(4)减排措施进行系统阐述,以期为反刍动物的高效、低碳养殖提供理论依据。

封孔器锥面端头与钻孔残留煤渣的力学作用分析及应用

分析封孔器锥面端头与钻孔残留煤渣的力学作用,有助于利用锥面端头的减阻效应,提高封孔器的送入孔深与速度。首先,在锥面端头受力分析基础上,推导了锥面端头移动最小推力计算公式,并通过试验研究验证了其正确性;然后,分析了堆积煤渣承受的侧向力,并揭示了锥面端头减阻机理;最后,应用理论研究结果,提出了锥面端头优化设计思路,改进了封孔器,并开展了现场试验。试验结果表明:锥面端头移动最小推力与端头重力、端头锥面角度、端头锥面与煤渣的最大静摩擦系数、堆积煤渣厚度和端头锥底半径均呈正相关性关系(与锥面角度呈正切函数关系);锥面端头通过降低堆积煤渣厚度及接触面顶端堆积煤渣剪切应力实现减阻;改进型封孔器可以降低阻力、提高送入速度与孔深。

机械损伤对果蔬采后品质的影响及其控制方法

机械损伤是鲜活果蔬采后常见的损伤之一。机械损伤会导致果蔬出现细胞膜破裂、营养与水分流失、果蔬呼吸速率加剧、成熟进程加快、果蔬软化、微生物侵染几率增加,严重影响鲜活农产品的质量和保质期,同时机械损伤会引发果蔬产生相应防御反应。清楚地了解机械损伤机制以及危害对于果蔬采后品质的优化控制至关重要。该文系统论述有关机械损伤对鲜活果蔬采后品质影响的研究进展,综述果蔬机械损伤现有的控制技术,旨在为鲜活农产品的运输贮藏提供理论指导。

食品中杂环胺在机体中的代谢机制和减控措施的研究进展

杂环胺作为一类热诱导形成的有害物,广泛存在于富含蛋白质的高温加工食品中。经体内代谢活化后具有较强的致癌和致突变性,可对机体造成严重危害。该文详细综述了杂环胺的分类、在不同食品中的含量及检测方法、代谢机制、毒性作用及其减控措施,以充分揭示食品有害物杂环胺发挥毒性作用的机理,以期为其毒性控制和探索新型减控措施提供参考。

壁湍流的复合减阻及能流分析

湍流减阻的技术与机理具有重要的科学和工程意义。近年来,研究者对壁湍流的减阻策略和机理开展了多方位探索。本文回顾了摩阻的能流分析框架,该框架将摩阻系数和能量耗散率定量地结合了起来,清晰地给出了驱动能量和控制能量在相干、随机和平均流动中的耗散原理,该框架的分析思路对复杂控制情况仍然适用;介绍了展向对吹射流引发的大尺度环流减阻方法,该方法可有效地完成速度条带的卷并,抑制流向涡的生成,减弱近壁湍流强度,在摩擦雷诺数为180的槽道流中可达到最佳约19%的减阻率,实现了通过输入相干能量减小湍流随机耗散的控制目标;展示了结合大尺度环流和壁面吹吸气的复合控制方法的优势,该方法实现了远超单一控制方法的减阻效果,在摩擦雷诺数为180时达到最佳约33%的减阻率和32%的净能量节省率。在前人研究的基础上,本文检验了在含肋壁面上施加大尺度环流控制的复合方案,验证了大尺度环流控制的鲁棒性,发现壁面小肋能够在一定程度上减小大尺度环流二次涡的影响,从而有效提升壁面小肋的减阻效率。

汽车机械变速器的降噪设计及维修措施研究

由于部分汽车机械变速器会产生一定的噪音,对人们的使用造成了较大影响,为了解决这一问题,针对齿轮、箱体、轴承刚性提出了一系列的降噪措施。并提出了汽车机械变速器维修时存在的问题,包括换挡冲击较大、变速器打滑、变速器异响等等,针对这一问题,提出了提高齿轮精度及强度、提高润滑油油量及质量、及时更换滤清器及油底垫的维修措施。

大口径顶管穿越粉细砂层技术难题及应对措施

本文介绍了某内径4m的钢筋混凝土顶管穿越粉细砂层的工程实例,整个顶管过程中,遇到了顶进机头“磕头”现象、顶进阻力成倍增加和顶进纠偏困难等众多问题,通过重新计算和分析,在顶进过程中通过增加中继间数量和一些减阻措施,并且在机头进洞前采取了加固粉细砂地层的方法,有效地控制了机头的进洞误差,使工程顺利贯通,为相关类似工程提供参考。

小麦机收损失的原因及减损措施

为提升小麦的收割速度,机械化收获成为最重要的收割手段。但机械化收割存在着收获损失的问题。基于此,文章探讨了小麦收割中机收损失产生的主要原因,包括小麦品种、收获时间、收获机技术状态、操作人员技术水平等。进而提出了小麦机收减损的有效措施,包括选择优良小麦品种、做好收获机的养护和调整、提高操作人员水平,建立机械化收获标准和机械设备操作规范,以保证小麦生产的高产高效。

THE INVESTIGATION OF VORTEX METHOD AND ITS APPLICATION TO DRAG REDUCTION TECHNOLOGY

The flow past a circular cylinder and airfoil with varying mathematical roughness function are numerically simulated. A new model about blowing and suction is constructed by using the concept of mathematical roughness function. The flow field and the drag are investigated through this new model. By the numerical study about bluff body, some conclusions are drawn to reduce the drag.

Method of suspender line trajectory design

Based on the mechanical model of an elastic rod,a new trajectory design method was established.The advantages of the suspender line trajectory in reducing drag and torsion were compared,and the main controlling factors of drag and torque and their influence rules were analyzed.Research shows that the suspender line trajectory reduces drag and torque more effectively than the conventional trajectory in a certain parameter interval and has more controllable parameters than that of the catenary trajectory.The main factors affecting the drag reduction and torque reduction of the suspender line trajectory include the friction coefficient,vertical distance,horizontal distance,and deviation angle at the initial point in the suspended section.The larger the friction coefficient and deviation angle,the less the drag reduction and torque reduction.The suspender line trajectory has the best drag reduction effect when the horizontal and vertical distances are more than 3000 m and the ratio is close to 1.5.The drag in sliding drilling can be reduced up to 60%,and the torque in rotary drilling can be reduced by a maximum of 40%.Therefore,the trajectory design of the suspender line has unique application prospects in deep extended-reach wells.

减阻-渗吸-驱泄协同开发技术机理及应用

低渗透油藏是胜利油区重要的产油阵地之一,其储量占油田总储量的20%以上。低渗透储层具有孔喉半径细小、非均质性强的特点,导致水驱过程出现注入压力高、难注入等问题。目前主要采取活性剂降压增注、高压注水、缩小注采井距等措施来提高开发效果,但仍存在有效时间短、单井注入量低、单井采出液量低、波及体积小等生产问题,因此,开展新型高效的开发方式刻不容缓。“十三五”以来,开展了水井增注补能、采油井渗吸增油、注采井间驱泄扩波及协同开发方式,可以实现提高驱替压力梯度、增强水驱、提高采收率的目的。该协同开发模式在纯化油田开展了矿场应用,纯化油田62区块水井的注入压力降低20%,注水量提高25%,对应的采油井单井日产油量由0.45t/d增至5.08t/d,增产效益明显,整体采收率提高8%以上。

平板仿生沟槽表面减阻性能数值模拟研究

本文借助AnsysFluent开展平板仿生沟槽表面减阻性能数值模拟研究,系统分析沟槽形状、几何尺寸等参数对其减阻性能的影响。数值模拟结果表明,平板表面仿生沟槽的存在使得平板表面的剪应力大幅减小,且可以大幅降低平板表面的速度梯度,因而可以起到减阻的效果。另外,通过对比分析3种不同沟槽形状平板的减阻性能发现,V形沟槽的减阻性能较U形和L形减阻性能更优,在后续设计中可考虑V形沟槽。