纳米流体强化驱油机理研究进展

纳米流体强化驱油技术对于降低石油开采成本和提高石油采收率具有十分重要的意义。关于纳米流体强化驱油机理的研究,近年来取得了一系列重要成果。本文重点阐述了关于纳米流体驱油机理的相关基础研究工作,在综合不同学术观点和研究成果的基础上归纳了纳米流体强化驱油的四种机理,据此指出在结构分离压力、岩石润湿性改变和油水界面张力降低的共同作用下使得纳米流体在驱油过程中表现出“卷起”与“扩散”的双重特征,从而具有强化驱油作用。最后指出纳米流体在提高石油采收率领域内将具有非常广阔的应用前景,但是对纳米流体的驱油效果以及影响因素还需进行大量的研究。此外,将纳米流体驱油与泡沫驱油有效结合是一种值得探索的提高石油采收率途径。     

凹槽微通道铜-水纳米流体传热与流动分析

对铜-水纳米流体在圆弧型凹槽微通道中的传热与流动特性进行了分析。比较了不同体积分数的铜-水纳米流体在深宽比分别为0.3和0.5的凹槽微通道中的温度和速度分布,分析了体积分数和凹槽深宽比对凹槽微通道中铜-水纳米流体的传热系数和流体输运动力因子的影响。凹槽强化了微通道对流传热,与平板型微通道相比,铜-水纳米流体在圆弧型凹槽微通通内呈现出不同的传热特性。纳米流体体积分数、流体输运动力因子和凹槽深宽比对凹槽强化微通道传热影响较大。分析结果与已有的实验结果符合较好。     

纳米流体强化传热研究分析

文中综述了目前国内外对于纳米流体强化传热技术的研究情况,分析了纳米流体的强化传热机理及添加纳米粒子后对液体的物性参数--粘度、比热、密度、流体流动的影响;说明了石墨/水纳米流体及Fe3O4/水纳米流体导热系数和对流换热系数测量实验的原理及结果,并对结果进行了分析,实验结果表明纳米流体强化了传热.     

Numerical investigation of the effects of geometric parameters of heaters on mixed covection in a lid‐driven cavity filled with different nanofluids

In this paper, the effects of the thicknesses and locations of two rectangular heaters, located on the bottom and one side of on an enclosure, on mixed convection of nanofluid flows in a lid‐driven cavity are numerically investigated. The enclosure is simultaneously heated partially by these two heaters which have similar or different thicknesses and also filled with different nanofluids containing nanoparticles of Cu, Ag, Al₂O₃, and TiO₂ within the base fluid of water. A finite volume approach by the SIMPLE algorithm is used to solve the governing equations. The effects of different Rayleigh numbers (), Reynolds numbers (), solid volume fractions (), heater lengths (), heater locations () and heater thicknesses () on the streamlines, isotherms and the average Nusselt number along two heaters are studied accurately. Also, variations of average Nusselt number of two heaters are considered whenever one heater is fixed and the other heater moves along on the wall. Moreover, variations of the length of one heater on the average Nusselt number are also studied whenever the length of the other heater is fixed. In addition, variations of the thickness of one heater on the average Nusselt number are studied whenever the thickness of the other heater is fixed.     

Flow and heat transfer in a porous medium saturated with a Sisko nanofluid over a nonlinearly stretching sheet with heat generation/absorption

This work is focused on steady flow and heat transfer in a porous medium saturated with a Sisko nanofluid (non‐Newtonian power‐law) over a nonlinearly stretching sheet in the presence of heat generation/absorption. Nonlinear PDEs are transformed into a system of coupled nonlinear ODEs with related boundary conditions using similarity transformation. The reduced equations are then solved numerically using the Runge–Kutta–Fehlberg fourth–fifth order method (RKF45) with Maple 14.0 software. The solutions depend on the power‐law index n and the effect of pertinent parameter such as the Brownian motion parameter, thermophoresis parameter, Lewis number, the permeability, and the heat generation/absorption on the dimensionless velocity, temperature, and nanoparticles volume fraction and also on the skin friction, local Nusselt, and Sherwood numbers are produced for values of the influence parameter. A rapprochement of the numerical results of the actual study with formerly published data detected an excellent agreement.     

中低温环境下Al_2O_3-乙醇纳米流体稳定性的研究

采用"两步法"制备浓度为1.0%且不含分散剂的Al2O3-乙醇纳米流体,研究了中低温环境下温度变化对Al2O3-乙醇纳米流体稳定性的影响。采用紫外吸光度方法评价了纳米流体的稳定性;测试了悬浮颗粒的粒径分布并拟合出不同温度下粒径分布随时间的变化关系,计算了悬浮颗粒的沉降速率并拟合出不同温度下沉降速率随时间的变化关系;从势垒值变化的角度解释了温度影响纳米流体稳定性的原因。结果显示,Al2O3-乙醇纳米流体能在低温下保持较好的稳定性。     

Peristaltic activity of thermally radiative magneto-nanofluid with electroosmosis and entropy analysis

The importance of gold and silver nanoparticles in the blood flow has immense applications in biomedicine for the treatment of cancer disease and wound treatment due to their large atomic number and antimicrobial property. The current study deals with the magnetohydrodynamic and electroosmotic radiative peristaltic Jeffrey nanofluid (blood–silver/gold) flow with the effect of slip and convective boundary conditions in the nonsymmetric vertical channel. The nondimensional governing equations have been solved analytically and the exact solutions have been presented for velocity, temperature, shear stress, trapping, entropy generation, pressure gradient and heat transfer coefficient. The pictorial representations have been prepared for the flow quantities with respect to fluid flow parameters of interest. It is noticed from the current study that the gold-based nanofluids exhibit higher velocity than silver-based nanofluids. Enhancement of thermal radiation decreases the total entropy generation. The size of the tapered bolus decreases with the enhancement of magnetic field strength. The present model is applicable in designing pharmacodynamic pumps and drug delivery systems.     

Impact of volume fraction and fluid layer thickness on heat transfer effectiveness of water-based nanofluids

The heat transfer effectiveness of nanofluids is adversely affected by the delay in convection onset. The lesser effectiveness, when compared to that of base fluid, is observed in a range of nanofluid layer thickness. The heat transfer coefficient of water–Al₂O₃ nanofluid can be enhanced by sustaining the equilibrium between Rayleigh number, temperature, particle volume fraction, and enclosure aspect ratio. In this paper, the specific correlation of fluid layer thickness and the onset of convection, which can significantly dominate the heat transfer characteristics of nanofluids are investigated using the concept of critical Rayleigh number. The water layer thickness for convection onset is first experimentally assessed for different real-life heat flux densities. It is then performed for Al₂O₃–water nanofluid for varying volume fractions. With the increase in volume fraction even though thermal conductivity increases, the overall heat transfer enhancement of the nanofluid is reduced. Temperature involved (heat flux density), the volume fraction of the nanofluid used, nanofluid layer thickness (space availability for the cooling system), and mass of the nanoparticle influence heat transfer enhancement. A higher volume fraction may not always result in enhancement of heat transfer as far as nanofluids are concerned.     

Maxwell nanofluid heat and mass transfer analysis over a stretching sheet

The Buongiorno model Maxwell nanofluid flow, heat and mass transfer characteristics over a stretching sheet with a magnetic field, thermal radiation, and chemical reaction is numerically investigated in this analysis. This model incorporates the effects of Brownian motion and thermophoresis. The governing partial differential equations are transformed into a coupled nonlinear ordinary differential equation by using the similarity transformation technique. The resultant nonlinear differential equations are solved by using the Finite element method. The sketches of velocity, temperature and concentration with diverse values of magnetic field parameter (0.1 ≤ M ≤ 1.5), Deborah number (0.0 ≤ β ≤ 0.19), radiation parameter (0.1 ≤ R ≤ 0.7), Prandtl number (0.5 ≤ Pr ≤ 0.8), Brownian motion parameter (0.1 ≤ Nb ≤ 0.7), thermophoretic parameter (0.2 ≤ Nt ≤ 0.8), Chemical reaction parameter (1.0 ≤ Cr ≤ 2.5) and Lewis number (1.5 ≤ Le ≤ 3.0) have investigated and are depicted through plots. Moreover, the values of the Skin-friction coefficient, Nusselt number, and Sherwood numbers are also computed and are shown in tables. The sequels of this analysis reviewed that the values of Skin-friction coefficient and Sherwood number intensified with hiked values of Deborah number (β), whereas, the values of Nusselt number decelerate as values of (β) improves.     

Unsteady nanofluid flow between two spinning expanding disks with continuous vertical motion under the influence of modified Hall effect

The principle aim of this article is to detect the effects of externally applied magnetic force in the nanofluid flow, flowing between two co-axially rotating and expanding disks where the upper disk is continuously moving vertically upward and downward. Also, the modified Hall Effect has been considered as an effective factor of the flow. The lower disk is vertically static. The rotation and vertical motion of the disks create a three-dimensional flow of nanofluid. Heat and mass density along with the motion of the flow has been analyzed under the variation in magnetic and Hall parameters. The findings have been compared with the results in Von Karman flow of nanofluid between two rotating and stretching disks. The velocity components have been largely influenced by magnetic and Hall parameters in case of downward movement of the upper disk. The fluid temperature is detected higher in case of upward velocity and lower in case of the downward motion of the upper disk. The heat transferability of the disks is effected differently at two different disks with the influence of magnetic force and Hall effect.