Capillary force of a novel skew-grooved wick structure for micro heat pipes

In order to improve the capillary force of grooved wick, a novel skew-grooved wick structure was proposed for micro heat pipes. Risen meniscus experiments were carried out to research the capillary force of the skew-grooved and rectangle-grooved wick and a comparison of capillarity between the two wick structures was explored. A theoretical capillary force model of skew-grooved wick structure was also developed to calculate its effective capillary radius by comparing with the rectangle-grooved wick. From the experimental results, the maximum capillary force of the skewed-grooved wick is 8.62% larger than that of the rectangle-grooved wick. From the theoretical analysis, because the skewed-grooved wick has a smaller effective capillary radius, its maximum capillary force is 8.64% larger than that of the rectangle-grooved wick. The results indicate that the skew-grooved wick provides larger capillary force than the rectangle-grooved wick.

Theory and application of numerical simulation method of capillary force enhanced oil production

A kind of second-order implicit upwind fractional step finite difference methods are presented for the numerical simulation of coupled systems for enhanced （chemical） oil production with capillary force in the porous media. Some techniques, e.g., the calculus of variations, the energy analysis method, the commutativity of the products of difference operators, the decomposition of high-order difference operators, and the theory of a priori estimate, are introduced. An optimal order error estimate in the l2 norm is derived. The method is successfully used in the numerical simulation of the enhanced oil production in actual oilfields. The simulation results are satisfactory and interesting.

Simulation and Experiments on the Capillary Force between a Circular Disk and a Parallel Substrate

The capillary force of a liquid bridge with a pinned contact line between a small disk and a parallel plate is investigated by simulation and experiments. The numerical minimization simulation method is utilized to calculate the capillary force. The results show excellent agreement with the Young-Laplace equation method. An experimental setup is built to measure the capillary force. The experimental results indicate that the simulation results agree well with the measured forces at large separation distances, while some deviation may occur due to the transition from the advancing contact angle to the receding one at small distances. It is also found that the measured rupture distance is slightly larger than the simulation value due to the effect of the viscous interaction inside the liquid bridge.

A capillary force model for interactions between two spheres

Based on the method of energy principle, an analytical approach for computing the capillary force for sphere/sphere geometry is presented in this paper. In modeling the capillary force, we consider spheres with both equal and non-equal radii, for both symmetric and asymmetric configurations at liquid/solid interfaces. We use numerical analysis to investigate the validity and efficiency of the derived model. The effect of various parameters including humidity, distance between two spheres, radii of spheres and contact angles on the meniscus force are investigated. Finally the results obtained from the model are compared with experimental measurements, and the accuracy and precision of the presented approach is verified.

Polyelectrolyte Multilayer Patterns Created by Capillary Force and Their Impact on Cell Migration

Cell migration plays a crucial role in a variety of physiological and pathological processes.In this study a method of capillary force lithography was used to treat poly(sodium 4-styrenesulfonate) (PSS)/poly(diallyldimethylammonium) chloride (PDADMAC) multilayers with a PDMS stamp before or after etching by NaC1 solution,yielding physical patterns with various features such as double thin lines,double strips,meniscus-shaped ridges,and high ridges.The ridge height is controllable in the range of 25 and 1100 nm.Migration of smooth muscle cells (SMCs) was restrained by the double-line patterns in a ridge height-dependent manner.By contrast,the mobility of SMCs was controlled by both the hydration ratio of the multilayers and the pattern features.

Capillary bridges and capillary forces between two axisymmetric power-law particles

Capillary interactions are fundamentally important in many scientific and industrial fields. However, most existing models of the capillary bridges and capillary forces between two solids with a mediated liquid, are based on extremely simple geometrical configurations, such as sphere-plate, sphere-sphere, and plate-plate. The capillary bridge and capillary force between two axisymmetric power-law profile particles with a mediated constant-volume liquid are investigated in this study. A dimensionless method is adopted to calculate the capillary bridge shape between two power-law profile particles based on the Young-Laplace equation. The critical rupture criterion of the liquid bridge is shown in four forms that produce consistent results. It was found that the dimensionless rupture distance changes little when the shape index is larger than 2. The results show that the power-law index has a significant influence on the capillary force between two power-law particles. This is directly attributed to the different shape profiles of power-law particles with different indices. Effects of various other parameters such as ratio of the particle equivalent radii, liquid contact angle, liquid volume, and interparticle distance on the capillary force between two power-law particles are also examined.

Regularity analysis of wrinkles under the action of capillary force in an annular thin film

The wrinkling law of annular sheet which is induced by capillary force with inner liquid film is analyzed in this paper.The results show that the inner liquid film can wrinkle the annular sheet when the surface tension of the liquid film reaches a critical value,and the critical value can be dramatically altered by changing the geometry and properties of the annular sheet.The results obtained in this article may hold potential applications in generating three-dimensional structures through capillary effects.

Effect of micro-dimple patterns on capillary pull-off force and friction force of silicon surface

A microtribometer is used to measure and compare pull-off forces and friction forces exerted on （a） micro-dimpled silicon surfaces, （b） bare silicon surfaces, and （c） octadecyltrichlorosilane （OTS） treated silicon surfaces at different relative humidity （RH） levels separately. It is found that above a critical RH level, the capillary pull-off force increases abruptly and that the micro-dimple textured surface has a lower critical RH value as well as a higher pull-off force value than the other two surfaces. A micro topography parameter, namely sidewall area ratio, is found to play a major role in controlling the capillary pull-off force. Furthermore, micro-dimpled silicon surface is also proved to be not sensitive to variation in RH level, and can realize a stable and decreased friction coefficient compared with un-textured silicon surfaces. The reservoir-like function of micro dimples is considered to weaken or avoid the breakage effect of liquid bridges at different RH levels, thereby maintaining a stable frictional behaviour.

Influence of atomic force microscope(AFM) probe shape on adhesion force measured in humidity environment

In micro-manipulation, the adhesion force has very important influence on behaviors of micro-objects. Here, a theoretical study on the effects of humidity on the adhesion force is presented between atomic force microscope （AFM） tips and substrate. The analysis shows that the precise tip geometry plays a critical role on humidity depen- dence of the adhesion force, which is the dominant factor in manipulating micro-objects in AFM experiments. For a blunt （paraboloid） tip, the adhesion force versus humidity curves tends to the apparent contrast （peak-to-valley corrugation） with a broad range. This paper demonstrates that the abrupt change of the adhesion force has high correla- tion with probe curvatures, which is mediated by coordinates of solid-liquid-vapor contact lines （triple point） on the probe profiles. The study provides insights for further under- standing nanoscale adhesion forces and the way to choose probe shapes in manipulating micro-objects in AFM experiments.

油团聚体系中桥液作用机理的研究

试验及计算结果表明,桥液用量决定着体系中起主导作用的力——毛细作用力的大小,直接影响聚团粒度、形状和强度。毛细作用力的本质是由于液一气界面张力及由于桥液优先润湿疏水性矿粒、形成弯曲液面时所产生的附加压力的合力。计算结果还可以对油团聚体系中其它许多现象进行圆满解释,是对DLVO理论的补充、发展。

A collagen-based electrolyte-locked separator enables capacitor to have high safety and ionic conductivity

The conventional liquid electrolytes(LEs) have a high level of ionic conductivity;however, they often suffer from the poor processability and safety risks of potential leakage. Although solid-state electrolytes(SSEs) can solve these inherent problems of LEs, the ionic conductivity of most SSEs is several magnitudes lower than these of LEs. Herein, we report a novel strategy by building liquid ion-transport channels in a solid framework and prepared an electrolyte-locked separator(ELS) using a collagen fiber membrane(CFm). The liquid electrolyte was primarily infiltrated in the smaller voids of CFm, and its ionic conductivity could attain to 9.0×10-3 S cm-1 when the electrolyte absorption(EA) reached up to 112.0%. After centrifuging treatment, the electrolyte retentions(ER) and ionic conductivities of ELS were 108.93% and 8.37×10-3 S cm-1, respectively, which were much higher than those of commercial cellulose separator(CS), exerting excellent liquid-locking performances. In particular, the electrical double-layer capacitors(EDLC) assembled by ELS or CS were characterized and exhibited similar electrochemical performance,demonstrating the satisfactory ability and applicability of ELS for commercial use. In addition, the ELSbased EDLC exhibited favorable flexibility with relative lower loss of capacitance under different angles of bending.

Sweat detection theory and fluid driven methods: A review

In recent years, analyses of sweat have become more popular since it doesn't require invasive sampling procedures. Although blood still remains the golden standards in clinical, analyses of other common body fluids,such as sweat, have become increasingly important. Because the compositions of sweat and blood are osmotically related, the content of certain metabolites in sweat can directly reflect the disease. Sweat detection can be used as an alternative to blood detection and allows continuous monitoring. Increased development of wearable sensors makes it possible for continuous sweat detection. Here, this paper gave a review about the sweat detection methods, such as fluorescence sensing, electrochemical sensing and colorimetric sensing. The advantages and disadvantages of each method and their developing trend in sweat detection were summarized. Then, for the problem of continuous sweat sampling, three methods(capillary force, hydrogel osmotic pump, evaporationdriven micropump) were introduced through different structures of microfluidic chip, and the level of sweat collection and transport achieved by related research was demonstrated. This review aims to provide guidance for future research in sweat detection and stimulate further interest in continuous monitoring of sweat using microfluidic chip.

Water blocking effect caused by the use of hydraulic methods for permeability enhancement in coal seams and methods for its removal

To research techniques for removing the water blocking effect caused by hydraulic applications in coal seams,the use of surfactants is proposed,based on the mechanics of the water blocking effect.Centrifugal experiments were used to validate the effects of using surfactants;the results show that after dealing with vacuum saturation with water,the volume of micropores decreases,which results in a larger average pore size,and the volume of transitional pores,mesopores,macropores and total pores increases.Based on the distribution of pore size,the operation mode of ‘‘water infusion after gas extraction,then continuing gas extraction" is recommended to improve the volume of coal mine gas drainage.When the reflectance of vitrinite in coal samples is less than 1,using the surfactants Fast T,1631,APG,BS can mitigate the damage caused by the water blocking effect.But when the reflectance of vitrinite is larger than 1.4,the damage caused by the water blocking effect can be increased.When the surfactant CMC is used in hydraulic applications,the capillary forces of coal samples are almost negative,which means the capillary force is in the same direction as the gas extraction.The direction of capillary forces benefits the gas flow.So,using CMC can play an active role in removing the water blocking effect.Centrifugal experiments confirm that using CMC can effectively remove the water blocking effect,which has a beneficial effect on improving the gas drainage volume.

Alignment of Nanoscale Single-Walled Carbon Nanotubes Strands

Depositing single-walled carbon nanotubes(SWNTs) with controllable density, pattern and orientation on electrodes presents a challenge in today's research. Here, we report a novel solvent evaporation method to align SWNTs in patterns having nanoscale width and micronscale length. SWNTs suspension has been introduced dropwise onto photoresist resin microchannels; and the capillary force can stretch and align SWNTs into strands with nanoscale width in the microchannels. Then these narrow and long aligned SWNTs patterns were successfully transferred to a pair of gold electrodes with different gaps to fabricate carbon nanotube field-effect transistor(CNTFET). Moreover, the electrical performance of the CNTFET show that the SWNTs strands can bridge different gaps and fabricate good electrical performance CNTFET with ON/OFF ratio around 106. This result suggests a promising and simple strategy for assembling well-aligned SWNTs into CNTFET device with good electrical performance.

Innovative Production of PCMs （Phase Change Materials） Preparation by Vacuum Impregnation： Thermal and Physical Properties

Energy is essential for every human activity for more comfortable life but also consumes more natural resources. In order to control human comfort, temperature usually required when the differences in temperature swing between indoor and outdoor temperatures. PCMs （phase change materials） are the high latent heat materials which can be used in building materials for energy conservation purpose. PCMs can store thermal energy and also can prevent heat to pass through temperature control areas. Paraffin has been used as PCMs are absorbed into the pore of fly ash as paraffin/fly-ash composite and mixed into the buildings materials. Paraffin is an organic material with high melting point （-59℃）, and nonflammable materials therefore paraffin can be used as the building materials for the function of PCMs for energy saving purposes. Composite PCMs can be prepared by vacuum impregnation process. Paraffin in liquid form will be impregnated into the pore of fly ash by vacuum capillary force to form paraffin/fly ash composite PCMs. Vacuum impregnation pressures, vacuum times, impregnation times of liquid paraffin in fly ash pores and temperatures for melting the solid paraffin into the liquid form are all affect on the thermal properties of paraffin/fly ash composite PCMs. Paraffin or PCMs impregnation are also relate to the physical property including the fractal dimensions of the pores of the fly ash particles and paraffin/fly ash composite PCMs. The fractal dimensions of the pore of fly ash and paraffin/fiy ash composites PCMs are between the values of 1.0 and 2.0. Fractal dimensions of paraffin/fly-ash composite PCMs have the same trend as the thermal properties for heat capacity and latent heat of melting. These fractal dimensions technique is a novel method to measure physical property of building material related to latent heat and heat capacity.

Sorption Hysteresis of Hardened Cement Pastes

Mesopores in porous solids can produce a pronounced sorption hysteresis at moderate and high reduced vapor pressures of the ambient gas that is condensed in the pores. Unlike to other conventional porous materials, cement pastes often behave exceptionally. The water sorption hysteresis frequently persists at very low humidity. This hysteresis is reflected in a corresponding hysteresis loop of the solid skeleton volume. We discuss a theoretical model based on the strong compression force exerted by a condensate on the walls of narrow slit pores embedded in an elastic solid. This compression force is shown to be capable of shifting walls of narrow slit pores. Humidity-dependent closing and reopening of slit pores can produce hysteresis loops even at low humidity.

Computational modelling of gas–liquid–solid multiphase free surface flow with and without evaporation

Gas–liquid–solid multiphase systems are ubiquitous in engineering applications,e.g.inkjet printing,spray drying and coating.Developing a numerical framework for modelling these multiphase systems is of great significance.An improved,resolved computational fluid dynamics-discrete element method(CFD-DEM)framework is developed to model the multiphase free surface flow with and without evaporation.An improved capillary force model is developed to compute the capillary interactions for partially floating particles at a free surface.Three well-known benchmark cases,namely drag coefficient calculation,the single sphere settling,and drafting-kissing-tumbling of two particles are conducted to validate the resolved CFD-DEM model.It turns out that the resolved CFD-DEM model developed in this paper can accurately calculate the fluid–solid interactions and predict the trajectory of solid particles interacting with the liquid phase.Numerical demonstrations,namely two particles moving along a free surface when the liquid phase evaporates,and particle transport and accumulations inside an evaporating sessile droplet show the performance of the resolved model.

Unidirectional transport of both wettable and nonwettable liquids on an asymmetrically concave structured surface

Unidirectional liquid transport(UDLT)has been widely used in various fields as an important process for transferring both mass and energy.However,UDLT driven by a structural gradient has been witnessed for a long time only in wettable liquids.For nonwettable liquids,UDLT can hardly proceed merely by a structural gradient.Herein,we propose an asymmetrically concave structured surface(AMC-surface),featuring tip-to-base periodically arranged pyramid-shaped concave structures with a certain degree of overlap,which enables the UDLT of both wettable and nonwettable liquids.For wettable liquids,the capillary force along each corner leads to the UDLT pointing toward the base side of the concave pyramid,while for nonwettable liquids,the UDLT is attributable to the static liquid pressure overwhelming the repulsive Laplace pressure induced by the asymmetric grooves and overlapping part.As a result,both wettable and nonwettable liquids transport spontaneously and unidirectionally on the AMC-surface with no energy input.Moreover,the concave structure endows good mechanical stability and can be easily prepared using a facile nail-punching approach over a large area.We also demonstrated its application in a continuous chemical reaction in a confined area.We envision that the unique UDLT behavior on the as-developed AMC-surface will shed new light on the programmable manipulation of various liquids.

Capillary shrinkage of graphene oxide hydrogels

Conventional carbon materials cannot combine high density and high porosity,which are required in many applications,typically for energy storage under a limited space.A novel highly dense yet porous carbon has previously been produced from a three-dimensional(3D)reduced graphene oxide(r-GO)hydrogel by evaporation-induced drying.Here the mechanism of such a network shrinkage in r-GO hydrogel is specifically illustrated by the use of water and 1,4-dioxane,which have a sole difference in surface tension.As a result,the surface tension of the evaporating solvent determines the capillary forces in the nanochannels,which causes shrinkage of the r-GO network.More promisingly,the selection of a solvent with a known surface tension can precisely tune the microstructure associated with the density and porosity of the resulting porous carbon,rendering the porous carbon materials great potential in practical devices with high volumetric performance.

Experimental simulation of capillary effect on rough flat surfaces

The movement of the liquid column inside the slit was utilized to experimentally simulate the characteristics of the capillary force per unit length for different rough flat surfaces.The movement of the liquid column was achieved by continuously changing the slit interval.The maximum climb height and contact angle of the liquid column were observed during this process to study the relationship between capillary force and contact surface roughness.Based on the assumption that the microstructures on the rough surfaces are of the same form and continuously and uniformly distributed,it is shown that the capillary force per unit length under homogeneous wetting is independent of the roughness.For heterogeneous wetting,the capillary force per unit length is positively correlated with the roughness.The results also indicate that the appearance of"contact line pinning"is caused by insufficient capillary force along the direction of liquid column movement.