Controlling the shape of fluid streams is important across scales: from industrial processing to control of biomolecular interactions. Previous approaches to control fluid streams have focused mainly on creating chaotic flows to enhance mixing. Here we develop an approach to apply order using sequences of fluid transformations rather than enhancing chaos. We investigate the inertial flow deformations around a library of single cylindrical pillars within a microfluidic channel and assemble these net fluid transformations to engineer fluid streams. As these transformations provide a deterministic mapping of fluid elements from upstream to downstream of a pillar, we can sequentially arrange pillars to apply the associated nested maps and, therefore, create complex fluid structures without additional numerical simulation. To show the range of capabilities, we present sequences that sculpt the cross-sectional shape of a stream into complex geometries, move and split a fluid stream, perform solution exchange and achieve particle separation. A general strategy to engineer fluid streams into a broad class of defined configurations in which the complexity of the nonlinear equations of fluid motion are abstracted from the user is a first step to programming streams of any desired shape, which would be useful for biological, chemical and materials automation.
The connection between fluid flow and optical flow is explored in typical flow visualizations to provide a rational foundation for application of the optical flow method to image-based fluid velocity measurements. The projected-motion equations are derived, and the physics-based optical flow equation is given. In general, the optical flow is proportional to the path-averaged velocity of fluid or particles weighted with a relevant field quantity. The variational formulation and the corresponding Euler-Lagrange equation are given for optical flow computation. An error analysis for optical flow computation is provided, which is quantitatively examined by simulations on synthetic grid images. Direct comparisons between the optical flow method and the correlation-based method are made in simulations on synthetic particle images and experiments in a strongly excited turbulent jet.
Recent experimental and theoretical studies demonstrate that pressure driven flow of fluids through nanoscale (d < 10 nm) carbon pores occurs 4 to 5 orders of magnitude faster than predicted by extrapolation from conventional theory. Here, we report experimental results for flow of water, ethanol, and decane through carbon nanopipes with larger inner diameters (43 ± 3 nm) than previously investigated. We find enhanced transport up to 45 times theoretical predictions. In contrast to previous work, in our systems, decane flows faster than water. These nanopipes were composed of amorphous carbon deposited from ethylene vapor in alumina templates using a single step fabrication process.
We consider the problem of liquid and gas flow in micro-channels under conditions of a small Knudsen and Mach numbers, that correspond to continuum model. Data from the literature on pressure drop in circular, rectangle, triangular and trapezoidal micro-channels with hydrodynamic diameter ranging from 1.01 μm to 4010 μm are analyzed. The Reynolds number at transition from laminar to turbulent flow is considered. Attention is paid to comparison between predictions of the conventional theory and experimental data, obtained during the last decade, as well as to discussion of possible sources of unexpected effects which were revealed by a number of previous investigations.
Stylolites-products of intergranular pressure-solution-are laterally extensive, planar features. They are a common strain localization feature in sedimentary rocks. Their potential impact on regional fluid flow has interested geoscientists for almost a century. Prevalent views are that they act as permeability barriers, although laboratory studies are extremely rare. Here we report on a systematic laboratory study of the influence of stylolites on permeability in limestone. Our data demonstrate that, contrary to conventional wisdom, the studied stylolites do not act as barriers to fluid flow. In detail, when a stylolite occurs perpendicular to the direction of flow, the permeability simply follows the same power law permeability-porosity trend as the stylolite-free material. We show, using a combination of high-resolution (4 mu m) X-ray computed tomography, optical microscopy, and chemical analyses, that the stylolites of this study are not only perforated layers constructed from numerous discontinuous pressure solution seams, but comprise minerals of similar or lower density to the host rock. The stylolites are not continuous high-density layers. Our data affirm that stylolites may not impact regional fluid flow as much as previously anticipated.
Light-emitting diodes (LEDs) are widely used in our daily lives. Both light and heat are generated from LED chips and then transmitted or conducted through multiple packaging materials and interfaces. Part of the transmitted light converts into heat along the light propagation; in return, the accumulation of heat leads to the degradation of light output. The accumulated heat negatively influences the reliability and longevity of LEDs, and thus thermal management is critical for LED packaging and applications. On the other hand, in LED packaging processes, many fluid flow problems exist, such as phosphor coating, silicone injection, chip bonding, solder reflow, etc. Among them, phosphor coating is the most important process which is essential for LED performance. Phosphor gel is a kind of non-Newton fluid and its coating process is a typical fluid-flow problem. Overall, since LED packaging and applications present many heat and fluid flow problems, obtaining a full understanding of these problems enables advancements in the development of LED processes and designs. In this review, the emphasis is placed on heat generation in chips, heat flow in packages and application products, fluid flow in phosphor coating process, etc. This is a domain in which significant progress has been achieved in the last decade, and reporting on these advances will facilitate state-of-the-art LED packaging and application technologies.
Thick evaporite sequences deposited in saline giant basins are traditionally viewed as impermeable barriers to fluid flow. This paradigm has recently been challenged by documented evidence of fluid migration pathways through several-km thick series of evaporites, such as the late Miocene (Messinian) sediments in the Mediterranean basin, deposited during the Messinian Salinity Crisis (MSC). Our paper reviews the occurrence of fluid expulsion events in these evaporites in the depocentres of the basin, and analyses their potential as seal-bypass systems. The Messinian salt giant was deposited in peculiar conditions where massive sea-level changes occurred in a relatively limited time interval, and a thick basin-centre evaporitic series was deposited between pre-MSC and post-MSC deep-water sediments. Consequently, rapid water and sediment loading/unloading events contributed to the creation of overpressures up to fracture and possibly lithostatic gradient, causing the fluids to be released in explosive events. Examples of fluid expulsion events are here grouped and classified in relation to the long and short term effects of the Messinian Salinity Crisis, as well as the local controls and pre-conditioning basin factors. While peaks of fluid expulsion activity during the short time-frame of the MSC can be mainly linked to Mediterranean-wide events, local controls appear to play a major role in post-MSC fluid mobilisation. In these cases, evaporite breach is largely dependent on the availability of pre-MSC undersaturated fluid sources and the capability of the pre-MSC sediments to be overpressured. The analysis here presented can be used as a basis to understand the controls on syn- and post-depositional movement of fluids in sedimentary basins. Moreover, the analysis of temporal and spatial distribution of fluid expulsion events can help define hydrocarbon migration style and pathways in deep-seated petroleum plays.
We present a reconstruction of episodic fluid flow over the past similar to 250 k.y. along the Malpais normal fault, which hosts the Beowawe hydrothermal system (Nevada, USA), using a novel combination of the apatite (U-Th)/He (AHe) thermochronometer and a model of the thermal effects of fluid flow. Samples show partial resetting of the AHe thermochronometer in a 40-m-wide zone around the fault. Numerical models using current fluid temperatures and discharge rates indicate that fluid flow events lasting 2 k.y. or more lead to fully reset samples. Episodic fluid pulses lasting 1 k.y. result in partially reset samples, with 30-40 individual fluid pulses required to match the data. Episodic fluid flow is also supported by an overturned geothermal gradient in a borehole that crasses the fault, and by breaks in stable isotope trends in hydrothermal sinter deposits that coincide with two independently dated earthquakes in the past 20 k.y. This suggests a system where fluid flow is triggered by repeated seismic activity, and that seals itself over similar to 1 k.y. due to the formation of clays and silicates in the fault damage zone. Hydrothermal activity is younger than the 6-10 Ma age of the fault, which means that deep (similar to 5 km) fluid flow was initiated only after a large part of the 230 m of fault offset had taken place.
Cytosolic fluid dynamics have been implicated in cell motility(1-5) because of the hydrodynamic forces they induce and because of their influence on transport of components of the actin machinery to the leading edge. To investigate the existence and the direction of fluid flow in rapidly moving cells, we introduced inert quantum dots into the lamellipodia of fish epithelial keratocytes and analysed their distribution and motion. Our results indicate that fluid flow is directed from the cell body towards the leading edge in the cell frame of reference, at about 40% of cell speed. We propose that this forward-directed flow is driven by increased hydrostatic pressure generated at the rear of the cell by myosin contraction, and show that inhibition of myosin II activity by blebbistatin reverses the direction of fluid flow and leads to a decrease in keratocyte speed. We present a physical model for fluid pressure and flow in moving cells that quantitatively accounts for our experimental data.
Laminar liquid–water flow and heat transfer in three-dimensional wavy microchannels with rectangular cross section are studied by numerical simulation. The flow field is investigated and the dynamical system technique (Poincaré section) is employed to analyze the fluid mixing. The results show that when liquid coolant flows through the wavy microchannels, secondary flow (Dean vortices) can be generated. It is found that the quantity and the location of the vortices may change along the flow direction, leading to chaotic advection, which can greatly enhance the convective fluid mixing, and thus the heat transfer performance of the present wavy microchannels is much better than that of straight microchannels with the same cross section. At the same time, the pressure drop penalty of the present wavy microchannels can be much smaller than the heat transfer enhancement. Furthermore, the relative wavy amplitude of the microchannels along the flow direction may be varied for various practical purposes, without compromising the compactness and efficiency of the wavy microchannels. The relative waviness can be increased along the flow direction, which results in higher heat transfer performance and renders the temperature of the devices much more uniform. The relative waviness can also be designed to be higher at high heat flux regions for hot spot mitigation purposes.