Laminar Flow In Microchannels Research Articles

Pressure Drop of Fully-Developed, Laminar Flow in Microchannels of Arbitrary Cross-Section

Abstract The pressure drop of fully developed, laminar, incompressible flow in smooth mini- and microchannels of arbitrary cross-section is investigated. A compact approximate model is proposed that predicts the pressure drop for a wide variety of shapes. The model is only a function of geometrical parameters of the cross-section, i.e., area, perimeter, and polar moment of inertia. The proposed model is compared with analytical and numerical solutions for several shapes. Also, the comparison of the model with experimental data, collected by several researchers, shows good agreement.

Influence of Ribbon Structure Rough Wall on the Microscale Poiseuille Flow

The regular perturbation method is introduced to investigate the influence of two-dimensional roughness on laminar flow in microchannels between two parallel plates. By superimposing a series of harmonic functions with identical dimensional amplitude as well as the same fundamental wave number, the wall roughness functions are obtained and the relative roughness can be determined as the maximal value of the product between the normalized roughness functions and a small parameter. Through modifying the fundamental wave number, the dimensionless roughness spacing is changed. Under this roughness model, the equations with respect to the disturbance stream function are obtained and analyzed numerically. The numerical results show that flowing in microchannels are more complex than that in macrochannels; there exist apparent fluctuations with streamlines and clear vortex structures in microchannels; the flow resistances are about 5–80% higher than the theoretical value under different wall-roughness parameters. Furthermore, analysis shows that the effect of roughness on the flow pattern is distinct from that on the friction factor.

Gravity-induced reorientation of the interface between two liquids of different densities flowing laminarly through a microchannel

This paper experimentally quantifies the reorientation of the liquid-liquid interface between fluids of different densities flowing side-by-side in pressure-driven laminar flow in microchannels. A gravity-induced pressure mismatch at the interface will gradually drive the denser fluid to occupy the lower portion of the microchannel. The rate of this process is expected to depend on the interplay of viscous forces--which tend to dominate at the microscale-and inertial and gravitational forces. A correlation that relates the position of such a liquid-liquid interface to physical variables and channel dimensions was derived. The extent of reorientation of the streams was then related to two dimensionless numbers: Fr, the square root of the ratio of inertial to gravitational forces; and Re/Fr2, the ratio of gravitational to viscous forces. Further analysis showed that the reorientation of the streams depends only on the gravitational and viscous forces, but not inertia. The quantitative description of the position of the interface between liquids of different densities described in this paper aids in the rational design of the rapidly growing number of microchemical systems that utilize multistream laminar flow for performing spatially resolved chemistry and biology inside microfluidic channels.

Pressure drops of single and two-phase flows through T-type microchannel mixers

In this paper, preliminary experimental results are presented on pressure drop characteristics of single and two-phase flows through two T-type rectangular microchannel mixers with hydraulic diameters of 528 and 333 μm, respectively. It is shown that both N 2 and water single-phase laminar flows in microchannels, with consideration of experimental uncertainties, are consistent with classic theory, if additional effects, such as entrance effects that will interfere with the interpretation of experimental results, are eliminated by carefully designing the experiments. The obtained pressure drop data of N 2–water two-phase flow in micromixers are analyzed and compared with existing flow pattern-independent models. It is found that the Lockhart–Martinelli method generally underpredicts the frictional pressure drop. Thereafter, a modified correlation of C value in the Chisholm’s equation based on linear regression of experimental data is proposed to provide a better prediction of the two-phase frictional pressure drop. Also among the homogeneous flow models investigated, the viscosity correlation of McAdams indicates the best performance in correlating the frictional pressure drop data (mean deviations within ±20% for two micromixers both). Finally it is suggested that systematic studies are still required to accurately predict two-phase frictional performance in microchannels.

Oscillating laminar electrokinetic flow in infinitely extended rectangular microchannels

This paper has addressed analytically the problem of laminar flow in microchannels with rectangular cross-section subjected to a time-dependent sinusoidal pressure gradient and a sinusoidal electric field. The analytical solution has been determined based on the Debye–Hückel approximation of a low surface potential at the channel wall. We have demonstrated that Onsager's principle of reciprocity is valid for this problem. Parametric studies of streaming potential have shown the dependence of the electroviscous effect not only on the Debye length, but also on the oscillation frequency and the microchannel width. Parametric studies of electroosmosis demonstrate that the flow rate decreases due to an increase in frequency. The obtained solutions for both the streaming potential and electroosmotic flows become those for flow between two parallel plates in the limit of a large aspect ratio.

FRACTAL CHARACTERIZATION OF WALL ROUGHNESS ON PRESSURE DROP IN MICROCHANNELS

A fractal dimension D for wall roughness in microchannels on silicon wafers is calculated. The fractal dimension of wall roughness in these microchannels fabricated at different etching conditions is found to be in the range from 1.02 to 1.69. We propose that the Darcy friction factor for laminar flow in microchannels of a specific cross-sectional area is a function of the Reynolds number Re (based on the hydraulic diameter), the ratio of the wall-roughness height to the hydraulic radius of the microchannel e/r, and the fractal dimension D. A correlation equation in terms of the above parameters is obtained for pressure drop in microchannels with rough surfaces

Microreactor: New Device for Organic and Enzymatic Synthesis

AbstractFor Abstract see ChemInform Abstract in Full Text.

Gradients of substrate-bound laminin orient axonal specification of neurons.

Little is known about the influence of substrate-bound gradients on neuronal development, since it has been difficult to fabricate gradients over the distances typically required for biological studies (a few hundred micrometers). This article demonstrates a generally applicable technique for the fabrication of substrate-bound gradients of proteins with complex shapes, using laminar flows in microchannels. Gradients that range from pure laminin to pure BSA were formed in solution by using a network of microchannels, and these proteins were allowed to adsorb onto a homogeneous layer of poly-l-lysine. Rat hippocampal neurons were cultivated on these substrate-bound gradients. Analysis of optical images of these neurons showed that axon specification is oriented in the direction of increasing surface density of laminin. Linear gradients in laminin adsorbed from a gradient in solution having a slope of nabla [laminin] > about 0.06 microg (ml.microm)(-1) (defined by dividing the change of concentration of laminin in solution over the distance of the gradient) orient axon specification, whereas those with nabla [laminin] < about 0.06 microg (ml.microm)(-1) have no effect.

マイクロリアクター 次世代型合成デバイス

This review summarized recent progress in synthetic chemistry in microchannel reactor, in which the feature of microchannel reactor itself and variety of reactions in microchannel reactor were presented. There is a basic difference between fluidic system in batch scale and that in microchannel which is caused by difference of those geometry. First, solution forms laminar flow in microchannel. Second, short diameter of microchannel enhances the efficiency of transport of mass and heat. Recent reports revealed that microchannel reactor is not only feasible tool for a safe and highly efficient reaction, also feasible tool for highly stereo-controlled or rapid reactions.

Experimental and theoretical scaling laws for transverse diffusive broadening in two-phase laminar flows in microchannels

This letter quantifies both experimentally and theoretically the diffusion of low-molecular-weight species across the interface between two aqueous solutions in pressure-driven laminar flow in microchannels at high Péclet numbers. Confocal fluorescent microscopy was used to visualize a fluorescent product formed by reaction between chemical species carried separately by the two solutions. At steady state, the width of the reaction–diffusion zone at the interface adjacent to the wall of the channel and transverse to the direction of flow scales as the one-third power of both the axial distance down the channel (from the point where the two streams join) and the average velocity of the flow, instead of the more familiar one-half power scaling which was measured in the middle of the channel. A quantitative description of reaction–diffusion processes near the walls of the channel, such as described in this letter, is required for the rational use of laminar flows for performing spatially resolved surface chemistry and biology inside microchannels and for understanding three-dimensional features of mass transport in shearing flows near surfaces.