共查询到18条相似文献，搜索用时 171 毫秒
1.
明渠是指人工渠道、天然河道以及非满管水流的管道,明渠水流具有共同的水力特征,即具有自由表面,且自由表面上的气体大气压,依靠重力能流动。明渠水流分为恒定流与非恒定流,明渠恒定流又分为明渠均匀流与明渠非均匀流。 相似文献
2.
明渠恒定非均匀渐变流水面线问题是非均匀流问题的关键也是教学的难点,文章对水面线的定性分析的教学过程做汇总整理,将这部分内容的教法做介绍。 相似文献
3.
非均匀流可分为渐变流和急变流。在明渠中渐变流的水深可能沿程逐渐增大,也可能逐渐减小,从而形成常见的壅水曲线或降水曲线;而明渠中急变流的水深可以在局部急剧增大,也可以在局部突然降低,从而形成常见的水跃或水跌。 相似文献
4.
通过建立数学模型,从能量守恒方程出发,合理简化沿程水头损失,研究恒定流量下水位沿程变化规律,然后根据上下游边界断面水位反算流量,从而推导出矩形明渠恒定非均匀流流量的简化算法。该方法反映了流场的场强为压强,流量恒定时水位仅随流程变化,方法简单可行,在可作为工程计算的估算解。 相似文献
5.
城市水系规划中水利计算具有断面汇水面积不易确定,水力交换复杂,流向不易确定,存在往复流现象,受水系边界条件影响显著,水系上控制建筑物种类繁多不能忽略等特点,传统的水利计算方法不能很好的适用于城市水系的水利计算。一维非恒定流水力计算是基于对水流运动的数学方法描述动态反映河网水流运动状态的方法,能很好满足城市水系规划对水利计算的要求。以广东省佛山市南海区里水水系整治规划中的水利计算为例,说明非恒定流方法在城市水系规划水利计算中的应用。 相似文献
6.
引水渠道明渠均匀流计算中通常采用的方法为试算法或图解法，本文介绍利用工程数学的迭代计算方法将明渠均匀流的常用计算公式转换成迭代计算公式，很方便地求解。该方法计算简单，结果精确，容易掌握，适合于多个渠道断面比选的计算。 相似文献
7.
以流线、流面、汇点的概念为基础,通过对稳定流双井干扰和直线隔水边界附近涌水量理论公式的对比分析,提出虚拟界面Ⅰ,运用流线、流面的性质,流线方程等给出证明。同时探讨其在基坑中的应用. 相似文献
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9.
沙坪二级水电站施工导流采用分期拦断河床、明渠导流方式,围堰全年挡水,导流运行时间长、流量大,需要通过导流模型试验对导流各项水力条件进行研究。通过1：70整体水力学模型,对导流明渠过水后的水流流速流态,上游围堰、下游围堰及下游河床等部位的冲刷情况进行了研究。研究表明：原设计方案在设计流量下,上、下游围堰堰顶不能满足挡水要求,导流明渠出渠水流归槽较差,下游冲刷严重。结合实验结果,作出增加明渠底宽,降低从坝轴线处明渠底高程,扩大明渠进口宽度、顺直出口右侧,调整上、下游围堰位置等优化措施。试验表明：新方案明显改善了原设计方案下出现的水力学问题。 相似文献
10.
黑石碛是长江上游典型的卵石滩险,具有急,浅,险的复杂水流条件。自向家坝水电站运行以来,在下游产生新的非恒定流,水位变化剧烈,水流条件复杂。根据多年的测图资料,对比分析红灯碛在向家坝水电站运行后的地形冲淤变化、深泓线变化、滩险演变和典型断面地形变化,并提出了相应的整治措施,为今后的整治提供了参考。 相似文献
11.
Harisha Ramachandraiah Sahar Ardabili Asim M. Faridi Jesper Gantelius Jacob M. Kowalewski Gustaf M?rtensson Aman Russom 《Biomicrofluidics》2014,8(3)
Passive particle focusing based on inertial microfluidics was recently introduced as a
high-throughput alternative to active focusing methods that require an external force field to
manipulate particles. In inertial microfluidics, dominant inertial forces cause particles to move
across streamlines and occupy equilibrium positions along the faces of walls in flows through
straight micro channels. In this study, we systematically analyzed the addition of secondary Dean
forces by introducing curvature and show how randomly distributed particles entering a simple
u-shaped curved channel are focused to a fixed lateral position exiting the curvature. We found the
lateral particle focusing position to be fixed and largely independent of radius of curvature and
whether particles entering the curvature are pre-focused (at equilibrium) or randomly distributed.
Unlike focusing in straight channels, where focusing typically is limited to channel cross-sections
in the range of particle size to create single focusing point, we report here particle focusing in a
large cross-section area (channel aspect ratio 1:10). Furthermore, we describe a simple u-shaped
curved channel, with single inlet and four outlets, for filtration applications. We demonstrate
continuous focusing and filtration of 10 μm particles (with >90% filtration
efficiency) from a suspension mixture at throughputs several orders of magnitude higher than flow
through straight channels (volume flow rate of 4.25 ml/min). Finally, as an example of high
throughput cell processing application, white blood cells were continuously processed with a
filtration efficiency of 78% with maintained high viability. We expect the study will aid in the
fundamental understanding of flow through curved channels and open the door for the development of a
whole set of bio-analytical applications. 相似文献
12.
Electrokinetic transport of cylindrical cells under dc electric fields in a straight microfluidic channel is experimentally and numerically investigated with emphasis on the dielectrophoretic (DEP) effect on their orientation variations. A two-dimensional multiphysics model, composed of the Navier–Stokes equations for the fluid flow and the Laplace equation for the electric potential defined in an arbitrary Lagrangian–Eulerian framework, is employed to capture the transient electrokinetic motion of cylindrical cells. The numerical predictions of the particle transport are in quantitative agreement with the obtained experimental results, suggesting that the DEP effect should be taken into account to study the electrokinetic transport of cylindrical particles even in a straight microchannel with uniform cross-sectional area. A comprehensive parametric study indicates that cylindrical particles would experience an oscillatory motion under low electric fields. However, they are aligned with their longest axis parallel to the imposed electric field under high electric fields due to the induced DEP effect. 相似文献
13.
In this paper, 3D particle focusing in a straight channel with asymmetrical expansion–contraction cavity arrays (ECCA channel) is achieved by exploiting the dean-flow-coupled elasto-inertial effects. First, the mechanism of particle focusing in both Newtonian and non-Newtonian fluids was introduced. Then particle focusing was demonstrated experimentally in this channel with Newtonian and non-Newtonian fluids using three different sized particles (3.2 μm, 4.8 μm, and 13 μm), respectively. Also, the effects of dean flow (or secondary flow) induced by expansion–contraction cavity arrays were highlighted by comparing the particle distributions in a single straight rectangular channel with that in the ECCA channel. Finally, the influences of flow rates and distances from the inlet on focusing performance in the ECCA channel were studied. The results show that in the ECCA channel particles are focused on the cavity side in Newtonian fluid due to the synthesis effects of inertial and dean-drag force, whereas the particles are focused on the opposite cavity side in non-Newtonian fluid due to the addition of viscoelastic force. Compared with the focusing performance in Newtonian fluid, the particles are more easily and better focused in non-Newtonian fluid. Besides, the Dean flow in visco-elastic fluid in the ECCA channel improves the particle focusing performance compared with that in a straight channel. A further advantage is three-dimensional (3D) particle focusing that in non-Newtonian fluid is realized according to the lateral side view of the channel while only two-dimensional (2D) particle focusing can be achieved in Newtonian fluid. Conclusively, this novel Dean-flow-coupled elasto-inertial microfluidic device could offer a continuous, sheathless, and high throughput (>10 000 s−1) 3D focusing performance, which may be valuable in various applications from high speed flow cytometry to cell counting, sorting, and analysis. 相似文献
14.
Chang H 《Endeavour》2007,31(1):7-11
Every schoolchild learns that, under standard pressure, pure water always boils at 100 degrees C. Except that it does not. By the late 18th century, pioneering scientists had already discovered great variations in the boiling temperature of water under fixed pressure. So, why have most of us been taught that the boiling point of water is constant? And, if it is not constant, how can it be used as a 'fixed point' for the calibration of thermometers? History of science has the answers. 相似文献
15.
Tam Vu Ali Rahimian Gulnaz Stybayeva Yandong Gao Timothy Kwa Judy Van de Water Alexander Revzin 《Biomicrofluidics》2015,9(4)
Monocytes represent a class of immune cells that play a key role in the innate and adaptive immune response against infections. One mechanism employed by monocytes for sensing foreign antigens is via toll-like receptors (TLRs)—transmembrane proteins that distinguish classes of foreign pathogens, for example, bacteria (TLR4, 5, and 9) vs. fungi (TLR2) vs. viruses (TLR3, 7, and 8). Binding of antigens activates a signaling cascade through TLR receptors that culminate in secretion of inflammatory cytokines. Detection of these cytokines can provide valuable clinical data for drug developers and disease investigations, but this usually requires a large sample volume and can be technically inefficient with traditional techniques such as flow cytometry, enzyme-linked immunosorbent assay, or luminex. This paper describes an approach whereby antibody arrays for capturing cells and secreted cytokines are encapsulated within a microfluidic device that can be reconfigured to operate in serial or parallel mode. In serial mode, the device represents one long channel that may be perfused with a small volume of minimally processed blood. Once monocytes are captured onto antibody spots imprinted into the floor of the device, the straight channel is reconfigured to form nine individually perfusable chambers. To prove this concept, the microfluidic platform was used to capture monocytes from minimally processed human blood in serial mode and then to stimulate monocytes with different TLR agonists in parallel mode. Three cytokines, tumor necrosis factor-α, interleukin (IL)-6, and IL-10, were detected using anti-cytokine antibody arrays integrated into each of the six chambers. We foresee further use of this device in applications such as pediatric immunology or drug/vaccine testing where it is important to balance small sample volume with the need for high information content. 相似文献
16.
Inertial microfluidics has brought enormous changes in the conventional cell/particle detection process and now become the main trend of sample pretreatment with outstanding throughput, low cost, and simple control method. However, inertial microfluidics in a straight microchannel is not enough to provide high efficiency and satisfying performance for cell/particle separation. A contraction–expansion microchannel is a widely used and multifunctional channel pattern involving inertial microfluidics, secondary flow, and the vortex in the chamber. The strengthened inertial microfluidics can help us to focus particles with a shorter channel length and less processing time. Both the vortex in the chamber and the secondary flow in the main channel can trap the target particles or separate particles based on their sizes more precisely. The contraction–expansion microchannels are also capable of combining with a curved, spiral, or serpentine channel to further improve the separation performance. Some recent studies have focused on the viscoelastic fluid that utilizes both elastic forces and inertial forces to separate different size particles precisely with a relatively low flow rate for the vulnerable cells. This article comprehensively reviews various contraction–expansion microchannels with Newtonian and viscoelastic fluids for particle focusing, separation, and microfluid mixing and provides particle manipulation performance data analysis for the contraction–expansion microchannel design. 相似文献
17.
The architecture of microfluidic networks can significantly impact the flow distribution within its different branches and thereby influence tracer transport within the network. In this paper, we study the flow rate distribution within a network of parallel microfluidic channels with a single input and single output, using a combination of theoretical modeling and microfluidic experiments. Within the ladder network, the flow rate distribution follows a U-shaped profile, with the highest flow rate occurring in the initial and final branches. The contrast with the central branches is controlled by a single dimensionless parameter, namely, the ratio of hydrodynamic resistance between the distribution channel and the side branches. This contrast in flow rates decreases when the resistance of the side branches increases relative to the resistance of the distribution channel. When the inlet flow is composed of two parallel streams, one of which transporting a diffusing species, a concentration variation is produced within the side branches of the network. The shape of this concentration gradient is fully determined by two dimensionless parameters: the ratio of resistances, which determines the flow rate distribution, and the Péclet number, which characterizes the relative speed of diffusion and advection. Depending on the values of these two control parameters, different distribution profiles can be obtained ranging from a flat profile to a step distribution of solute, with well-distributed gradients between these two limits. Our experimental results are in agreement with our numerical model predictions, based on a simplified 2D advection-diffusion problem. Finally, two possible applications of this work are presented: the first one combines the present design with self-digitization principle to encapsulate the controlled concentration in nanoliter chambers, while the second one extends the present design to create a continuous concentration gradient within an open flow chamber. 相似文献
18.
Vivian O&#x;Brien 《Journal of The Franklin Institute》1975,300(3):225-230
Solutions for pulsatile fully developed flow of Newtonian viscous fluid in a straight rectangular channel can be synthesized from analytic solutions of steady flow and oscillatory flow. A new steady solution is presented that is valid for all duct aspect ratios. Also new oscillatory solutions are given, showing dependence on a “viscous diffusion length”, the square root of the kinematic viscosity divided by frequency. 相似文献