Liquid Contact Research Articles

Numerical Investigation of Funicular Liquid Bridge Interactions Between Spherical Particles

AbstractIn industrial processing of wet particulate materials, the liquid governs the formation, growth, and breakup of particle agglomerates. Pendular liquid bridges between two particles have been extensively investigated in the literature. Despite the interest, the complexities in the funicular regime, which involve multiple spheres, have remained mostly uncovered. Validated numerical simulations are utilized herein to examine funicular liquid bridge shapes, interaction forces, and rupture conditions as functions of the liquid volume, pressure difference, interparticle distance, and contact angle for three‐sphere and four‐sphere arrangements, including the presence of a particle of different size. The agglomerate strength is quantitatively characterized for a broad range of conditions.

Wettability of Wood Surface Layer Examined From Chemical Change Perspective

The effect of artificial ageing on spruce (Picea abies), beech (Fagus sylvatica L.), birch (Betula pendula), and sessile oak (Quercus petraea) wood surfaces were investigated using qualitative (total phenolic and total soluble carbohydrate content) chemical examination methods. During ageing (∑240h), the influence of surface chemistry modifications was monitored by contact angle measurements of polar, dispersive (distilled water), and dispersive (diiodomethane) liquids. The results clearly show the relation between the ratio of main chemical components of the wood surface layer and surface wettability during artificial radiation. The identified surface chemistry modifications cause more significant change in the contact angle of polar and dispersive liquid, relative to the change of dispersive liquid contact angle. Chemical changes of the wood surface layer are due to the degradation of the main wood components (cellulose, hemicelluloses, and lignin) which can be properly monitored by total phenolic (TPC) and total soluble carbohydrate content (TSCC) measurements.

Semi-Analytical Correlation for Pool Boiling Heat Transfer Using Nanofluids Based on Fractal Theory

On the basis of fractal dispersion of active nucleation sites on boiling surface, a revised fractal model for nucleate pool boiling of nanofluids was established incorporating microlayer evaporation, nature convection and transient conduction. It has fewer empirical constants than that of traditional ones. Results of model using pure fluids and nanofluids conform to data from previous investigations. Thus, accuracy of model is verified. Effects of liquid properties and contact angle on pool boiling heat transfer coefficient (HTC) using nanofluids are discussed according to the present model. It is found that the HTC of nanofluid and the fractal dimension of nucleation sites decrease with the decreasing contact angle. The effect of liquid properties enhancement due to the presence of nanoparticles, has ignorable influence on HTC of dilute nanofluids while the decreased contact angle plays a more important role. It is also found that the surface with lower contact angle had a higher natural convection component.

Confluence of channel dimensions and groove width dictates slippery hydrodynamics in grooved hydrophobic confinements

Slippery hydrodynamics in grooved hydrophobic microchannels is known to be primarily dictated by the area of the gas–liquid contact surface. Here, we augment this classical notion by bringing out the critical role played by the channel dimensions on the underlying slip mechanisms and the consequent drag reduction. Our analysis, towards this, reveals the non-trivial implication of gas–liquid interface topology and its position inside the groove towards dictating the underlying frictional characteristics, which in turn is largely dependent on the confluence of the channel hydraulic diameter and the groove width. These results may turn out to be of immense consequence towards arriving at preferred frictional drag characteristics of hydrophobic microchannels and nanochannels by judicious choices of the pertinent geometric parameters.

Comparison of Different Commercial Conducting Materials as Ion-to-Electron Transducer Layers in Low-Cost Selective Solid-Contact Electrodes.

Simple, robust, sensitive and low-cost all-solid-state ion-selective electrodes (SCISEs) are of interest in different fields, such as medicine, veterinary, water treatment, food control, environmental and pollution monitoring, security, etc. as a replacement for traditional ion-selective electrodes with liquid inner contact. In spite of their potential advantages, SCISEs remain mainly in the research laboratories. With the motivation of developing simple and low-cost SCISEs with possible commercial applications, we report a comparison study of six different commercial conducting materials, namely, polypyrrole-block-polycaprolactone (PPy-b-PCaprol), graphene/poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) ink, poly(3,4-ethylenedioxythiophene):polyethylenglycol (PEDOT:PEG), high conductivity PEDOT:PSS, polyethylenimine (PEI) with PEDOT:PSS for their possible use as ion-to-electron transducer in polyurethane based pH-SCISEs. Among all studied pH-SCISES, PEDOT:PEG based electrodes exhibited the best results in terms of sensitivity, reproducibility and lifetime. Finally, these sensors were tested in different real samples showing good accuracy.

Microdroplet Contaminants: When and Why Superamphiphobic Surfaces Are Not Self-Cleaning.

Superamphiphobic surfaces are commonly associated with superior anticontamination and antifouling properties. Visually, this is justified by their ability to easily shed off drops and contaminants. However, on micropillar arrays, tiny droplets are known to remain on pillars’ top faces while the drop advances. This raises the question of whether remnants remain even on nanostructured superamphiphobic surfaces. Are superamphiphobic surfaces really self-cleaning? Here we investigate the presence of microdroplet contaminants on three nanostructured superamphiphobic surfaces. After brief contact with liquids having different volatilities and surface tension (water, ethylene glycol, hexadecane, and an ionic liquid), confocal microscopy reveals a “blanket-like” layer of microdroplets remaining on the surface. It appears that the phenomenon is universal. Notably, when placing subsequent drops onto the contaminated surface, they are still able to roll off. However, adhesion forces can gradually increase by up to 3 times after repeated liquid drop contact. Therefore, we conclude that superamphiphobic surfaces do not warrant self-cleaning and anticontamination capabilities at sub-micrometric length scales.

Dynamics of fluid-filled space multibody systems considering the microgravity effects

Many fluid-filled multibody systems have been used in the aerospace field. Many previous studies on the dynamics of these systems did not consider the microgravity acceleration effects. Under the microgravity acceleration action the fluid surface tension plays a dominant role in system's complex sloshing dynamic responses. An integrated computational methodology is proposed to study the nonlinear sloshing dynamics of fluid-filled space multibody systems under the actions of microgravity accelerations. The Smoothed Particle Hydrodynamics (SPH) method is used to describe the fluid and the absolute nodal coordinate formulation (ANCF) is used to describe the flexible bodies. To consider the liquid-gas interaction in the container of the fluid-filled multibody systems, a multiphase SPH model is adopted. The continuum surface force (CSF) model is adopted to treat the liquid-gas interface tension effects. A liquid static contact angle is defined to describe the liquid-solid contact interface. Finally, the effectiveness of the proposed methodology is validated by the four examples. Some new nonlinear sloshing dynamical behaviours of the space liquid-filled flexible multibody systems under the action of different gravitational accelerations are observed.

Evaluation of the gas absorption performance of a flow-type hydrate-based gas uptake system

As a means of assessing the viability of hydrate-based gas separation, this study examined the gas absorption performance of a flow-type gas–liquid contact device with static mixing. Assuming for the sake of simplification that the hydrate-based gas uptake occurred as a result of pseudo gas–liquid contact in a bubble-hydrate slurry solution, overall liquid side volumetric mass transfer coefficients were determined. An R134a–N2 mixture was used as a model gas because the corresponding hydrate readily forms under low pressure/high temperature conditions. At 0.325 MPa and 278 K, the average coefficients were determined to be in the range of 0.088–0.142 s−1. These values were more than ten times greater than those obtained from simple gas dissolution. The results of this work suggest that hydrate-based systems are preferable for the purpose of gas absorption and separation.

Polarisation independent liquid crystal lenses and contact lenses using embossed reactive mesogens

AbstractLiquid crystal lenses have promise in optical systems owing to their tunability combined with low electrical power, cost, and weight. A good example of such a system is switchable contact lenses for the correction of age‐related presbyopia. Sufficiently large phase modulation can be done using nematic liquid crystals in a meniscus lens configuration. However, the birefringent materials are inherently polarisation dependent, usually requiring orthogonal polarisations to be focussed separately. A novel method is presented for producing polarisation independent lenses based on reactive mesogens. Results are presented for a 2‐level and 3‐level diffractive Fresnel lenses, and the promise of the technique for use in refractive lenses such as contact lenses is discussed.

Durable anti-corrosive oil-impregnated porous surface of magnesium alloy by plasma electrolytic oxidation with hydrothermal treatment

Magnesium alloys have been widely employed for structural parts of aircrafts and automobiles to reduce their weight. However, magnesium alloys are easily corroded, thus practical applications always require protective coatings to guarantee satisfactory lifetime. In this study, we applied oil-impregnation and hydrophobizing to traditional plasma electrolytic oxidation (PEO) of magnesium alloy. Nanoporous hydroxide surface structure is fabricated by hydrothermal treatment of PEO-treated Mg alloy, then the self-assembled monolayer of perfluorodecyltrichlorosilane (FDTS) is coated for the hydrophobizing. The immiscible oil impregnation into the PEO-treated oxide layer with hydrothermal treatment and hydrophobizing significantly enhances the corrosion resistance as well as the mobility of water droplet on the surface. In addition, since the oil layer on the nanoporous surface inhibit the direct contact and penetration of corrosive liquid to the oxide layer, the oil-impregnated surface shows less degradation in corrosive liquid with long-term immersion than hydrophobic and superhydrophobic surface without oil-impregnation. These results indicates that oil-impregnated surface of Mg alloy has durable and robust anti-corrosion property.

Investigation of heat transfer coefficients in a liquid–liquid direct contact latent heat storage system

The study presents a latent heat storage system consisting of a phase change material (PCM) and a heat transfer fluid (HTF), placed in direct contact, for storing thermal energy derived from renewable energy sources or industrial waste heat. It is important that the two media are immiscible for the function of such a storage system. In this study the PCM was an eutectic mixture of the two salt hydrates, magnesium nitrate hexahydrate and magnesium chloride hexahydrate and the HTF was a mineral oil. The direct contact leads to intensified heat transfer compared to that in the indirect contact heat storage systems. This intensified heat transfer results in short loading and unloading periods of the storage tank with a high heat exchange performance. Furthermore, a higher storage density is observed in comparison to the sensible storage systems, particularly when combined with low temperature differences between the charged and discharged storage systems. In our study, the heat transfer between liquid PCM and liquid HTF (rises drop-shaped in the PCM) is investigated. For this purpose, a storage tank has been built with only one HTF inlet opening in the bottom. For the time and space resolved data, the axial temperature profile, and the surface temperature of the rising droplet, as well as the PCM temperature, are measured with a specially developed, fast, near infrared sensitive, and fiber-coupled technique. These measurements made it possible to determine a local heat transfer coefficient between the PCM and HTF. With the chosen parameters and materials in this study a heat transfer coefficient of 1845 W/m² K was calculated.

Recent advancements in solid-liquid triboelectric nanogenerators for energy harvesting and self-powered applications.

The abundance of water on earth provides a large window to utilize the mechanical energy within river currents and ocean waves. In this regard, hydropower harvesting through solid-liquid contact electrification has received considerable interest in the recent past. Despite advancements in nanotechnology, liquid energy harvesting devices, especially solid-liquid triboelectric nanogenerators (S-L TENGs), require efficient engineering of the interfacial properties of their substrates to transfer liquid mass and momentum rapidly with the effective generation/transfer of surface charges. To face this challenge, several parameters such as the selection of material, surface morphology and surface properties are currently being studied to develop a better system architecture for energy harvesting and self-powered application platforms with three different interacting modes of liquid contact. Moreover, several parameters of the contact solvents such as the ionic activity and polarity have been studied to understand the practical applicability of S-L TENGs to harvest energy from different natural and artificial resources. In addition, the scope of harvesting mechanical energy from other volatile organic compounds has been studied recently. Self-powered applications of S-L TENGs in various fields have also been demonstrated by different research groups. This work reviews recent progress in the development of S-L TENGs for the first time in terms of the different properties of solid and liquid contact materials along with their respective applications. Furthermore, the work concludes with perspectives, future opportunities, and major challenges of fabricating S-L TENGs as an efficient energy harvester.

Drop impact on hot plates: contact times, lift-off and the lamella rupture.

When a liquid drop impacts on a heated substrate, it can remain deposited, or violently boil in contact, or lift off with or without ever touching the surface. The latter is known as the Leidenfrost effect. The duration and area of the liquid-substrate contact are highly relevant for the heat transfer, as well as other effects such as corrosion. However, most experimental studies rely on side view imaging to determine contact times, and those are often mixed with the time until the drop lifts off from the substrate. Here, we develop and validate a reliable method of contact time determination using high-speed X-ray imaging and total internal reflection imaging. We exemplarily compare contact and lift-off times on flat silicon and sapphire substrates. We show that drops can rebound even without formation of a complete vapor layer, with a wide range of lift-off times. On sapphire, we find a local minimum of lift-off times that is much shorter than expected from capillary rebound in the comparatively low-temperature regime of transition boiling/thermal atomization. We elucidate the underlying mechanism related to spontaneous rupture of the lamella and receding of the contact area.

Surface construction of fluorinated TiO2 nanotube networks to develop uvioresistant superhydrophobic aramid fabric.

Poor ultraviolet (UV) resistance and good hydrophilicity lead to light aging of aramid fabrics and cause heat damage to the human body. This scenario occurs when the absorbed water by the fabric evaporates and forms high-temperature water vapor in a high-temperature fire environment, which may scald the human body. Herein, a superhydrophobic hollow TNT network structure was built on surfaces of aramid fibers by surface coating fluorinated TiO2 nanotubes (TNTs) to develop an air-permeable, UV-protective, and superhydrophobic coating. The as-prepared superhydrophobic aramid fabric exhibited highly superhydrophobic properties against various solutions of sauce, coffee, methylene blue, active red, Au nanoparticles, Ag nanoparticles, HCl, and NaOH with liquid contact angles up to 152–160°. In addition, the superhydrophobic fabric exhibited excellent UV aging resistance (UV protection factor was 100+; 74.58% of strength retention for 24 h of UV radiation compared with 55.15% of untreated fabric), a self-cleaning function against solid soil, and original wearing characteristics, including good breaking strength and air permeability. The developed superhydrophobic coating technology may promote practical application in high-temperature environments for aramid fabrics due to its good UV resistance, chemical resistance, poromericity, superhydrophobicity, anti-fouling, and self-cleaning properties.

Cost Effective Method for Pretreatment of Pearl Millet Biomass using Catalytic Down Flow Liquid Contact Reactor

The quest for alternative sources of energy generation that are inexpensive, eco-friendly, renewable and can re- place fossil fuels is owing to the increasing demands of energy. Production of biofuels from lignocellulosic biomass, holds remarkable potential to meet the current energy demand as well as to mitigate greenhouse gas emissions for a sustainable clean environment. Lignocellulose biomass feedstocks compulsorily undergo pretreatment process to release the fermentable sugars. The most of the existing pretreatment processes is energy intensive and con- sumes more cost. Low cost and effective pretreatment is essential to overcome the hurdles in commercialization of biofuel production from lignocellulose biomass. Catalytic Downflow liquid contact reactor (CDLCR) is an innovative method used to pretreat the lignocellulosic biomass, which consists of pump, electrical motor, circulation tank and pipe accessories. The present study deals with the pretreatment of pearl millet biomass using alkali catalyst (Ca (OH) 2) in a CDLCR under ambient conditions. Results of experimental trial show that there was significant re-duction in lignin and hemicellulose observed for pearl millet biomass. The minimum and maximum total reducing sugars observed at 10 and 60 min. of reaction time were 77.80 and 160.15 mg/g of biomass.

利用飞秒激光照射调控氧化石墨烯表面的浸润性能（特邀）

Modification of material surface morphology and properties based on femtosecond laser irradiation is a novel processing technology developed in recent years, which has shown unique advantages in high-speed, large-area and periodic subwavelength structure fabrications. Here this method was employed to rapidly fabricate uniform subwavelength grating structures on the surface of GO film, and then the processing mechanisms, the change of morphology and liquid wettability were investigated comprehensively. Through using different experimental parameters such as the laser power and the scanning speed, the rGO grating structures with variable depth-width ratios and surface roughness were obtained, leading to the controllable wettability with the liquid contact angles in a range of 15° to 75°, and their contact angles were found to increase by an average of 20° after 20 days in the air. Our work lays a solid foundation for femtosecond laser micro/nano-processing of two-dimensional materials. It is expected to have the future applications in the field of droplet collection, microfluidic control, and so on.

Characterization of the adhesive properties between structural battery electrolytes and carbon fibers

Structural batteries can simultaneously store electrical energy and carry mechanical load, being similar to both laminated carbon fiber composites and lithium ion batteries. The matrix in a structural battery must both conduct ions and transfer load between the fibers, made possible with a phase-separated combination of a solid polymer and a liquid electrolyte. This leads to a trade-off between the polymer contact creating adhesion and liquid contact creating ionic conductivity. Here we investigate the fiber-matrix adhesion between carbon fibres with different sizing and two different matrix systems, using microbond testing supported by transverse tensile tests. The results show that the mechanical adhesion of the fiber-matrix interface is lower than that of a commercial non-ion conducting polymer matrix but sufficient for structural battery applications.

Assessing micro- and nanoscale adhesion via liquid metal-based contact angle measurements in vacuum

Understanding wetting phenomena is of critical importance for various fields in theoretical and applied surface sciences as well as for the functionality of micro- and nanoelectromechanical systems. Contact angle measurement is one of the well-established methodologies for the wettability assessment of a surface. However, it faces major challenges when applied to micro- and nanoscale structures. Here, we exploit the superior properties of liquid metal alloys to contact angle measurement thus creating a methodology that allows for reliable examination of wetting phenomena on small-scale surface sections within the single-digit micrometer range and below. The technique applies electromigration to prepare oxide-free liquid metal droplets with diameters of less than ten micrometers in a vacuum environment, enabling a scanning electron microscope to be used for contact angle measurement. Static and dynamic contact angle measurements can be realized via the targeted manipulation of the droplets. The characterization of microscale surface sections with different nanoscale surface texture is demonstrated. Following this approach, unique characterization of wetting properties on the small scale becomes feasible. The methodology presented is therefore of significant importance for various emerging research fields such as micro- and nanorobotics as well as studies of few asperity contact mechanics on the micro- and nanoscale.

Closing the phosphorus cycle: Multi-criteria techno-economic optimization of phosphorus extraction from wastewater treatment sludge ash

The presence of heavy metals in concentrations above legal limit values is one of the main obstacles preventing closure of the phosphorus (P) cycle through directly applying wastewater treatment sludge ash as a fertilizer. Therefore, an alternative procedure is proposed to recover the valuable P from the sludge ash via wet chemical extraction. This comprehensive study uses several inorganic and organic acids, chelating agents and an alkaline solution to establish optimal and cost-effective conditions for wet P extraction from sludge ash. The optimization takes into account co-extraction of the following heavy metals: Cd, Cr, Cu, Ni, Pb and Zn. Design of experiments results show extraction liquid concentration, liquid/solid ratio and contact time all affect P and heavy metal extraction efficiency, both individually and through interaction. In addition, type of extraction liquid and pH at the end of the extraction procedure also affect P and heavy metal extraction efficiency. Combining results of XRD and SEM-EDX analysis with extraction data shows that at a pH <2, both Ca- and Al-phosphates in the ash dissolve easily. However, at slightly higher pH only Ca-phosphates dissolve well and at alkaline pH only Al-phosphates. The best trade-off between high P extraction, low heavy metal co-extraction and low operational costs is obtained with H2SO4 (0.5 N, 10 ml/g, 120 min) and oxalic acid (0.5 N, 12.8 ml/g, 120 min). H2SO4 outperforms the other extraction liquids in terms of extraction liquid costs per kg P extracted, whereas extraction with oxalic acid results in the lowest heavy metal co-extraction, thus reducing the downstream processing costs. None of the extraction liquids considered is appropriate for heavy metal removal prior to P extraction due to loss of P and insufficient heavy metal removal.

Modeling of capillary pressure in horizontal rough-walled fractures in the presence of liquid bridges

Capillary continuity between adjacent matrix blocks through formation of liquid bridge controls the recovery factor of gravity drainage process in fractured reservoirs. However, stability of liquid bridges as well as related capillary pressure in horizontal rough fractures is not well discussed in the available literature. In this work, new models of rough-walled fracture are developed and the role of roughness size and frequency on formation of liquid bridge and fracture capillary pressure are investigated. The Young-Laplace equation is numerically solved to characterize the liquid bridge formed in the proposed models of rough fractures. Critical fracture aperture for a range of liquid saturations, various roughness models and wettability conditions, is computed. Moreover, an expression is proposed to predict critical fracture aperture as a function of liquid saturation and contact angle for different models of rough fracture. Thereafter, as an interesting result, variation of fracture capillary pressure with liquid saturation, fracture aperture and wettability is evaluated for different models of rough fractures. It has been found that the trend of obtained fracture capillary pressure is similar to a typical matrix capillary pressure curve. The results also revealed that fracture capillary pressures as high as 1 psi (6.9 KPa) are viable when liquid saturation in the fracture is low (<5%) and fracture is sufficiently thin. Increasing wettability to liquid phase decreases the critical fracture aperture and enhances the fracture capillary pressure. At last, a semi-empirical model for capillary pressure as a function of effective fracture aperture, fracture roughness, contact angle and liquid saturation is proposed. The findings of this work help to better understand how liquid bridge stability and fracture capillary pressure may change in rough-walled horizontal fractures.