Capillary Flow Behavior Research Articles

Cotton threads encapsulated by thermal contraction tube for point-of-care diagnostics

Passive microfluidic devices based on capillary force are popular choices for point-of-care diagnostics. Paper, threads and cloth have been used to fabricate these microfluidic devices. Here, we introduced a novel method for packaging microfluidic thread-based analytical devices (μTADs) by encapsulating cotton threads in thermal contraction tubes. This package method can help to increase convenience during practice. At first, we investigate the influence of this package method on the capillary flow behavior and water absorption capacity of cotton threads. Then, we show the possibility of this package method in preparing μTADs with complex shapes. Lastly, we successfully use μTADs based on this package method for applications in point-of-care diagnostics including glucose detection in urine, fibrinogen detection in blood plasma, and plasma separation from whole blood samples and hematocrit (HCT) measurement. The package method is promising in expanding the applications of μTADs in point-of-care diagnostics.

Experimental and numerical study of solder bumps impact on the underfill fluid flow under electrohydrodynamic effect

Solder bumps can increase filling time, which is one of the main challenges in electronic packaging reliability. Here, we compare the capillary flow behavior between parallel plates with and without solder bumps to examine how solder bumps affect the length of the underfill fluid flow under the effects of an electric potential. We found that the solder bumps restrained the flow length, while the electric field enhanced it. By enhancing the voltage from 0 to 1000 V, in the case without solder bumps, the flow length increased by up to 30%, and it increased by up to 25% in the case of solder bumps. To determine the optimum bump design, we selected the diameter and pitch size of the solder bumps as the independent variables. The results revealed that larger pitch sizes and smaller diameters show longer fluid flow lengths. The effect of the electric field on varying nozzle positions was also investigated. We found that the fluid flow length increased when the nozzle was between the solder bumps compared to the top of the solder bumps. According to our observations, the nozzle position is also the main factor in determining the fluid flow length compared with the bump diameter and pitch sizes for the design of the underfill packaging process. Numerical simulations were also performed to compare the experimental results, and the average discrepancy between the experimental and numerical results at various time steps for different solder bump parameters was between 5 to 10%. Our findings demonstrate the potential of using electric potential in conjunction with solder bumps to control underfill flow, which can benefit flip-chip packaging applications. Numerical methods can accurately predict underfill fluid flow with solder bumps under the electric field effect.

Modeling Approach to Determine Static Rivulet Height in Regular Polygonal Capillary Tubes.

The rise of partially wetting liquids along the corners of noncircular capillary tubes is observed in many practical science and engineering applications such as wastewater treatment using membranes, remediation, oil recovery from petroleum reservoirs, and blood flow. In this paper, rivulet rise at the corners of polygonal capillary tubes is studied for partially wetting liquids with contact angles below the critical value. The presence of corners changes the distribution of a liquid in an incomplete wetting condition. In this study, geometrical models are proposed to better understand the capillary rise and flow behavior at the corners. A geometrical solution for the capillary rivulet height and profile is derived under gravity in triangular, square, and pentagonal capillary tubes. The effects of several factors including contact angle, number of polygon sides, and liquid properties on the capillary rivulet height are examined. It was found that the ratio of liquid surface tension to density directly affects the corner rise, while it has an inverse relationship with other factors. The maximum rivulet height of 91.6 mm is obtained in the triangular capillary tube with a side length of 1 mm and a contact angle of 30° for polydimethylsiloxane (PDMS-20)-air fluid pair. The minimum capillary rivulet height of 6.2 mm, on the other hand, is achieved in the pentagonal capillary tube, with a side length of 3 mm and a contact angle of 30°. To validate the developed analytical approach, comparisons are made between the model results, literature predictions, and experimental data. In addition, the geometrical model for a square capillary tube is compared with previous published studies, revealing a good agreement. This study provides quantitative results for the influence of capillary tube shape on the flow behavior of fluids in noncircular tubes that can be useful for control and optimization of transport phenomena in corresponding systems.

Characterisation of a vascular self-healing cementitious material system: Flow and curing properties

A series of characterisation studies are reported that provide new data on the behaviour of a self-healing cementitious material (SHCM) system. A ‘model’ material system is selected for study that comprises cyanoacrylate (CA) filled channels in concrete structural elements. The focus of the work is on transport and curing properties of the healing-agent, with the results of four separate studies being presented. The experimental programme encompasses the capillary flow behaviour of CA in a static natural crack, the sorption of healing-agent through a cracked surface into a concrete specimen, the development and progress of a CA curing front adjacent to a concrete substrate and the dynamic flow characteristics of CA in capillary channels. A theoretical relationship is established for each of these processes, which allows meaningful parameters to be determined that help characterise the behaviour of the material system. In all cases, the processes were shown to have a significant degree of variability but, equally, to exhibit strong behavioural trends.

Experimental study for the impacts of flow rate and concentration of asphaltene precipitant on dynamic asphaltene deposition in microcapillary medium

Asphaltenes have been referred to ‘cholesterol of petroleum’ and the heaviest and the most complex components in crude oil. Asphaltene aggregation and deposition have always been a challenging issue on fluid transport in porous media for oil recovery and production processes in industries. Many experimental efforts have been done to study asphaltene aggregation and deposition from crude oil. Most of these works were carried out by coreflood tests or in bulk solution. Only several macroscopic parameters, such as pressure variation and permeability reduction caused by asphlatene deposition, were studied. Few experimental studies have been done to make the direct pore-scale visualization of dynamic asphaltene deposition behavior in capillary flow. In this study, we developed a new experimental approach to directly visualize and measure the dynamic asphaltene deposition process in capillary flow. Effects of concentration of asphaltene precipitant and flowrate were examined. The results indicate that the concentration of precipitant has a significant effect on the dynamic asphaltene deposition in capillary flow. The size of asphaltene deposit increases significantly with elapsed time and size distribution becomes wider at higher precipitant concentration. Higher concentration of asphaltene precipitant could lead to higher deposition rate. The results also indicate that higher flowrate causes faster growth of asphaltene deposits in capillary flow. Larger sizes of asphaltene deposits are formed and number of asphaltene deposits decreases with the elapsed time at higher flowrate. The results produced provide new sights into the dynamic asphaltene deposition in capillary flow at a pore scale. They could contribute to predict the growth rate of arterial asphaltene deposition in porous media and develop accurate numerical simulator for enhanced oil recovery purpose in industries.

Capillary Flow Behavior of Polycarbonate (PC)/Acrylonitrile–Butadiene–Styrene (ABS) Blends

In this work, the flow behavior of polycarbonate / acrylonitrile-butadiene-styrene (PC/ABS) was investigated. The present blends with different ratios of PC and ABS were prepared by means of internal bath mixer. From the results of capillary rheometer, apparent shear rate, apparent shear stress, apparent viscosity, power law index, and flow activation energy at a constant shear rate and shear stress were determined. The results showed that the blends are pseudo plastic in behavior, and PC behaves in a relatively Newtonian manner but ABS exhibited significant shear thinning. In addition, the flow activation energy of the blends decreases with increasing shear rate while it increases with increasing shear stress.

Fine Pore Structure Characterization in Two Gessoes Using Focused Ion Bean Scanning

ABSTRACTThe movement of fluids through a porous medium is a function of the material type and the size and morphology of the voids. In the conservation of painted artworks, the movement of materials (for example, cleaning solutions) is a major factor in how a work reacts to treatments and a large influence on how the work will change with time. Of particular importance in the conservation of painted surfaces is the preparatory layer. This is a highly active transport medium because it is generally highly porous and a comparatively large and uniform component of a painted surface. In this work, a gesso film of calcium carbonate and rabbit skin glue, typical of the preparatory layer of many painted works, and an acrylic-based gesso film were imaged by focused ion beam (FIB) scanning. The gessoes were milled and scanned with gallium ions serially, in sequential planes orthogonal to the plane of the film. This yielded quantifiable measurements of the fine internal structures at a resolution far higher than previously reported for this type of material. This enabled a greater understanding of the geometry of the internal surfaces, increasing the understanding of the mechanics of capillary flow and diffusive behavior in this extremely common and significant material.

CFD modeling of pin shape effects on capillary flow during wave soldering

This paper presents an effective numerical method for evaluating the effect of the pin-through-hole (PTH) shape on the soldering stage using wave soldering technique. Three-dimensional finite volume numerical approach was employed to investigate capillary flow behavior when the PTH component with different pin shapes passes through molten solder (63Sn37Pb). An experiment was carried out on a single circular pin and compared with FLUENT simulation. Various PTH shapes, such as circle, triangle, square, rectangle, and hexagon, were modeled and meshed using computational fluid dynamics pre-processing software GAMBIT. The solder melt front was tracked using the volume of the fluid model. Using the circular PTH pin yielded the fastest front advancement during soldering, whereas the angle-edged PTH component increased the filling time and resulted in an uneven profile. Solder profile prediction was substantiated by experimental results. The current simulation results are expected to provide a better understanding of capillary action in various PTH geometrical shapes during wave soldering.

Effects of solder temperature on pin through-hole during wave soldering: thermal-fluid structure interaction analysis.

An efficient simulation technique was proposed to examine the thermal-fluid structure interaction in the effects of solder temperature on pin through-hole during wave soldering. This study investigated the capillary flow behavior as well as the displacement, temperature distribution, and von Mises stress of a pin passed through a solder material. A single pin through-hole connector mounted on a printed circuit board (PCB) was simulated using a 3D model solved by FLUENT. The ABAQUS solver was employed to analyze the pin structure at solder temperatures of 456.15 K (183°C) < T < 643.15 K (370°C). Both solvers were coupled by the real time coupling software and mesh-based parallel code coupling interface during analysis. In addition, an experiment was conducted to measure the temperature difference (ΔT) between the top and the bottom of the pin. Analysis results showed that an increase in temperature increased the structural displacement and the von Mises stress. Filling time exhibited a quadratic relationship to the increment of temperature. The deformation of pin showed a linear correlation to the temperature. The ΔT obtained from the simulation and the experimental method were validated. This study elucidates and clearly illustrates wave soldering for engineers in the PCB assembly industry.

Thermal Fluid-Structure Interaction in the Effects of Pin-Through-Hole Diameter during Wave Soldering

An effective simulation approach is introduced in this paper to study the thermal fluid-structure interaction (thermal FSI) on the effect of pin-through-hole (PTH) diameter on the wave soldering zone. A 3D single PTH connector and a printed circuit board model were constructed to investigate the capillary flow behavior when passing through molten solder (63SnPb37). In the analysis, the fluid solver FLUENT was used to solve and track the molten solder advancement using the volume of fluid technique. The structural solver ABAQUS was used to examine the von Mises stress and displacement of the PTH connector in the wave soldering process. Both solvers were coupled by MpCCI software. The effects of six different diameter ratios (0.1 &lt; d/ D &lt; 0.97) were studied through a simulation modeling. The use of ratio d/ D = 0.2 yielded a balanced filling profile and low thermal stress. Results revealed that filling level, temperature, and displacement exhibited polynomial behavior to d/ D. Stress of pin varied quadratically with the d/ D. The predicted molten solder profile was validated by experimental results. The simulation results are expected to provide better visualization and understanding of the wave soldering process by considering the aspects of thermal FSI.

Capillary Flow Behavior of the Carbon-black-filled Styrene-butadiene Rubber Compounds

Capillary Flow Behavior of the Carbon-black-filled Styrene-butadiene Rubber Compounds

Effect of carbon fiber on the capillary extrusion behaviors of high-density polyethylene

The capillary extrusion behaviors of high-density polyethylene (PE) containing carbon fibers (CF) were investigated from a viewpoint of their rheological properties. For values of CF content ranging from 0 to 5 wt%, the oscillatory moduli of PE slightly increased with CF content. Transient shear flow measurements showed that the steady shear viscosity and first normal stress difference of PE also slightly increased with the addition of CF. Conversely, the strain hardening behaviors of PE were suppressed by CF addition. It was found that CF becomes well dispersed in the PE matrix and that the elongation of the PE chain can be prevented by the presence of CF. The swell ratio of PE, which is the ratio of the diameters of the extrudate and the die, decreased with CF. Using a wide entrance angle die, PE/CF exhibited helical distortion at a higher output rate than that of PE. Using a narrow entrance angle die, sharkskin failure was observed in PE/CF at a higher output rate than in PE, although the helical distortion of PE was inhibited by CF. We discuss the origin of the helical distortion as an effect of CF on the swell behavior and the flow instabilities of PE in reference to the rheological behavior. We investigated the effect of carbon fiber (CF) on the capillary flow behavior of high-density polyethylene (PE). The presence of CF was found to have much great effect on reducing of the die swell of PE. CF could prevent the helical distortion of PE. The helical distortion of PE also changed to the sharkskin failure by adding CF. The extrusion behavior can be controlled by the addition of a small amount of CF.

Numerical simulation of the capillary flow in the meander microchannel

Pumping in microfluidic devices is an important issue in actuating fluid flow in microchannel, especially that capillary force has received more and more attractions due to the self-driven motion without external power input. However, less 2D simulation was done on the capillary flow in microchannel especially the meander microchannel which can be used for mixing and lab-on-a-chip (LOC) application. In this paper, the numerical simulation of the capillary flow in the meander microchannel has been studied using computer fluid dynamic simulation software CFD-ACE+. Different combinations of channel width in the X-direction denoted as Wx and Y-direction denoted as Wy were designed for simulating capillary flow behavior and pressure drop. The designed four types of meander microchannels (Wx × Wy) were 100 × 100 μm, 100 × 200 μm, 50 × 200 μm, and 50 × 400 μm. In this simulation results, it is found that the capillary pumping speed is highly depending on the channel width. The large speed change occurs at the turning angle of channel width change from Wx to Wy. The fastest pumping effect is found in the meander channel of 100 × 100 μm, which has an average pumping speed of 0.439 mm/s. The slowest average flow speed of 0.205 mm/s occurs in the meander channel of 50 × 400 μm. Changing the meander channel width may vary the capillary flow behavior including the pumping speed and the flow resistance as well as pressure drop which will be a good reference in designing the meander microchannels for microfluidic and LOC application.

3-D Numerical Simulation and Validation of Underfill Flow of Flip-Chips

A 3-D flow model, combined with the volume of fluid method, was developed to track capillary driven epoxy flow front, during the underfill process. Die edge effects and fillet spread based on the effect of process parameters were included in this model. Numerical results were validated against flow visualization data. Full field imaging experiments with quartz die were performed to observe flow front as a function of flow time. Development of this new modeling methodology focuses on predicting the capillary underfill flow behavior both in the first level interconnect area between a die and a substrate, and the area surrounding the die. This paper revealed that the edge flow effect contributes to pulling the overall flow front in the bump field area and formation of the fillet spread, which affects the risk associated with underfill delamination in flip chips. A comparative study, which included modeling results and experimental data, clearly indicated that the die edge effect cannot be neglected in order to capture the right trends of flow front shape evolution and an accurate fill time prediction. These comparisons also showed that the model developed in this paper is adequate to approximately simulate the fillet configuration all around the die after encapsulation of flip chips. The modeling methodology developed in this paper provides a fundamental understanding of underfill flow as a function of dispense process parameters, material properties, and package design parameters.

Wheat gluten‐based materials plasticised with glycerol and water by thermoplastic mixing and thermomoulding

Gluten has been investigated as a source for biodegradable polymeric materials because it is a renewable, available and low-cost raw material. The aim of this study was to evaluate the influence of some variables involved in the two stages of protein/plasticiser thermo-mechanical processing, where a mixture of glycerol and water was used as the plasticiser. Gluten/glycerol/water blends mixed under different thermal conditions (adiabatic starting at 25 °C and isothermal at 60 and 90 °C) exhibited shear thinning capillary flow behaviour, where a marked increase in flow properties was obtained at the highest temperature. Two thermal events, glass transitions related to the plasticiser blend and gluten, were detected by Modulated Differential Scanning Calorimetry (MDSC) and Dynamic Mechanical Analysis (DMA) tests. Moderate moulding temperature led to less resistant materials showing higher ductility, whereas higher mixing and moulding temperatures led to bioplastics with higher mechanical properties. A moulding temperature of 130 °C (close to the denaturation temperature) was found to be suitable for the thermomoulding process. In addition, the use of moderate mixing temperature seems to be convenient for those applications that required materials exhibiting high water absorption behaviour and suitable mechanical properties. Protein extractability results reflect the benefits of combining high shear and high temperature during processing to improve cross-linking reactions.

The Effects of Morphological and Wetting Properties of Porous Transport Layers on Water Movement in PEM Fuel Cells

A parametric study of the effect of wetting and in proton exchange membrane (PFM) fuel cells morphological properties of the cathode porous transport layer (PTL), also known as the gas diffusion layer (GDL), on water transport in proton exchange membrane (PEM) fuel cells has been conducted using a two-dimensional network model that captures the two-phase capillary flow behavior. The effect of PTL wetting properties is explored by considering four contact angle values. The effect of the morphology is analyzed using six pore size distributions. These six pore size distributions are generated by varying the scale and shape parameters in Weibull probability distribution functions. Also, the effect of a microporous layer (MPL) on water transport in the PTL is considered. Inclusion of the MPL resulted in a significant increase in the percolation pressure and a reduction in the PTL water content due to the formation of a few localized fingers which serve as water conduits. When defects in the MPL were considered, the PTL water content remained low with percolation pressures reduced to values similar to a PTL without an MPL.

Experimental study on capillary flow through polymer microchannel bends for microfluidic applications

Microchannel bends of rectangular cross-section were fabricated on polymethylmethacrylate (PMMA) by hot embossing, with a range of channel widths from 55 µm to 400 µm. The capillary movement of the interface between air and dyed water through the microchannels was recorded and analysed. The microfluidic flow behaviour as a function of the channel aspect ratio was studied. The evaluated Reynolds number was always less than 1.0 in each channel of every device. The air–water interface velocity in the devices was proportional to the channel aspect ratio. The air–water interface velocity shows a prominent increase at 90° separation angle. We observed an increasing trend of the air–water interface velocity with increasing channel aspect ratio. We have studied the separation of 10 µm polystyrene microparticles using a simple microchannel bend structure. We have obtained approximately 100% efficiency for the combined separation and clog-free blocking of 10 µm polystyrene microparticles using the above capillary flow behaviour in a modified microchannel bend structure.

A SAXS study of flow alignment of thermotropic liquid crystal mixtures

We report on the capillary flow behaviour of thermotropic liquid crystal mixtures containing 4-n-octyl-4′-cyanobiphenyl (8CB) and 4-n-pentyl-4′-cyanobiphenyl (5CB). The liquid crystal mixtures are studied in the Nematic (N) and Smectic (SA) phases at room temperature. Polarised optical microscopy (POM), rheology and simultaneous X-ray diffraction (XRD)/capillary flow experiments are performed to characterise the system. Polarised optical microscopy reveals a dramatic change in optical texture when the 5CB content is increased from 20 to 30% in the mixtures. X-ray diffraction results show that the system goes through a SA–N phase transition, such that the mixtures are smectic for 10–20% 5CB and nematic for 30–90% 5CB. Smectic mixtures flow with the layers aligned along the flow direction (mesogens perpendicular to flow) while nematic mixtures flow with the mesogens aligned in the flow direction. Simultaneous XRD/shear flow experiments show that the SA–N transition is independent of the flow rate in the range 1–6 ml min−1. The correlation length of the liquid crystal order decreases with increasing 5CB content. Rheology is used to prove that the correlation length behaviour is related to a reduction in the viscosity of the mixture.

β-Lactoglobulin Fibers under Capillary Flow

We describe the capillary flow behavior of gels of beta-lactoglobulin (beta-lg) containing droplets of fibrils and the shear flow alignment of beta-lg fibers in dilute aqueous solutions. Polarized optical microscopy and laser scanning confocal microscopy are used to show that capillary shear flow does not affect the fibril droplet sizes in the beta-lg gels, the system behaving in this respect as a solution of compact colloidal particles under shear flow. Small-angle X-ray scattering (SAXS) on dilute aqueous solutions indicates that the fibers can be initially aligned under capillary shear, but this alignment is lost after 18 min of shear. Transmission electron microscopy experiments on the samples studied by SAXS suggest that the loss of orientation is due to a shear-induced breakup of the swollen fibril network. Dynamic and static light scattering on dilute beta-lg fibril aqueous solutions are used to show that before shear beta-lg fibrils behave as strongly interacting semiflexible polymers, while they behave as weakly interacting rods after 18 min of capillary shear.

Capillary flow behavior of worm-like micelles studied by small-angle X-ray scattering and small angle light scattering

A novel capillary flow device has been developed and applied to study the orientation of worm-like micelles, among other systems. Small-angle X-ray scattering (SAXS) data from micelles formed by a Pluronic block copolymer in aqueous salt solution provides evidence for the formation of worm-like micelles, which align under flow. A transition from a rod-like form factor to a less persistent conformation is observed under flow. Flow alignment of worm-like micelles formed by the low molar mass amphiphile system cetyl pyridinium chloride+sodium salicylate is studied for comparative purposes. Here, inhomogenous flow at the micron scale is revealed by streaks in the small-angle light scattering pattern perpendicular to the flow direction. Copyright © 2006 John Wiley & Sons, Ltd.