Droplet Penetration Research Articles

Effects of position angles in twin-jet spray applications on droplet penetration of hydraulic nozzles

This study was conducted to determine the effects of different position angles in twin-jet spray applications on droplet penetration of different nozzle types. Seven different nozzle types (standard flat fan, ST; narrow flat fan, STN; multirange, LU; low-drift potential, AD; air-induction, IDK; twin-jet air-induction, IDKT) were used and nozzles were positioned +15° along the forward direction, perpendicular to ground surface 0? and reverse direction of forward -15°. Spray experiments at 100 L/ha constant application volume were conducted under controlled conditions of a closed facility. Water sensitive paper (WSP) was used as sampling surface. WSP samples were placed vertically and horizontally over both the metal frames and root collar of artificial plants. The present findings revealed that transport potential of spray droplets was quite lower on vertical planes than on horizontal planes. The greatest coverage was achieved with ST, STN, LU, and SC-type nozzles producing fine droplets. Compared to open targets, the coverage ratios around the root collars were quite low and insufficient. In all spray treatments, coverage ratio on the vertical planes was 86.1% lower than the coverage ratio on the horizontal plane. In other words, coverage ratio on the horizontal plane was 7.2 times greater than the coverage ratio on the vertical plane. Transfer efficiency of medium and coarse droplet-producing nozzles to root collars was greater than the transfer efficiency of fine droplet-producing nozzles. Such a ratio for AD, IDKT, and IDK-type nozzles was determined as 37.06, 37.85, and 41.02% respectively. According to the present findings, effects of nozzle position angle on droplet penetration were not found to be significant. However, nozzle position angle along the forward direction increased coverage ratios on the vertical planes.

Analysis of water droplet penetration in earth plasters using X-ray microtomography

Earth plasters are a very interesting solution for the coating of earthen construction, in terms of embodied energy, technical efficiency, while keeping the hygroscopic properties of the wall, unlike very little permeable coatings, as the cement-based ones. An experimental campaign has been conducted on several earth plasters which differs by their sand granulometry, earth origin and earth to sand ratio, leading to controlled surface topography and bulk properties. A novel X-ray microtomography technique adapted to such material has been relevant to observe directly the penetration of a water damping droplet inside the plaster with the 2D radiograph method, and enhance the understanding of the role of the surface and the bulk structure on it. A 3D scanning method was useful to understand the microstructure of the different samples and analyse their differences in terms of porosity. Two custom-made MATLAB codes have been developed in order to follow the droplet parameters inside the material, such as the spread, the penetration depth and the relative quantity of water along the time. Results show the consistent role of the surface topography on the water inertial penetration, while the penetration rate due to diffusion is directly linked to the bulk properties, and can be assimilated to a classic diffusion solution. The determination of the drying rate in the earth plasters highlights that the plasters which prevent the water to penetrate too deeply are also the ones which dry the slower, leading to a questioning on the role researched in an efficient coating material.

Droplet distributions in cotton harvest aid applications vary with the interactions among the unmanned aerial vehicle spraying parameters

A common problem of unmanned aerial vehicles (UAVs) spraying is that fewer droplets could reach the lower layer, and the depositions among the spray width show a significant difference. However, ensuring the penetration and uniformity of the spray is particularly important in the cotton harvest aid applications. As a new spraying method, poor droplet penetration and uniformity of droplet distribution may lead to inconsistent defoliation among canopy rows and poor defoliation in the lower part of the cotton canopy. The operational parameters of UAVs have remarkable effects on the droplet distribution, which will improve the defoliation rate of cotton. Therefore, full factorial tests were conducted in two experimental locations in the Xinjiang cotton-producing region in 2018 and 2019. The selected operational parameters in 2018 included the spray volume (three levels: 8.7, 12, and 15 L/ha), droplet size Dv50 (three levels: 100, 150, and 200 μm), and flight height (three levels: 1, 2, and 3 m). Meanwhile, the operational parameters in 2019 included the spray volume (three levels: 18, 22.5, and 30 L/ha) and droplet size Dv50 (three levels: 100, 150, and 200 μm). The main effects and interaction effects among the operational parameters were analyzed and discussed. The spray penetration and uniformity of droplet distribution were compared separately. The results show that flight height, spray volume, and droplet size have significant effects on spray penetration. Lowering the flight height of the drone, increasing the spray volume and Dv50 of droplets can improve the distribution of droplets at the bottom of the cotton canopy. As for droplet distribution uniformity, with the increase of the application volume and decrease of the flight height, the uniformity of the droplet distribution becomes worse. The influence of flight parameters on the uniformity of droplet distribution is very limited.

Novel Application of Electroslag Remelting Refining in the Removal of Boron and Phosphorus from Silicon Alloy for Silicon Recovery

With the shortage of high-grade silicon (Si) feedstock due to the rapid development of photovoltaic, electronic information, and organic Si industries, there is an increasing demand to recycle Si waste economically and efficiently. However, the deep removal of B and P from Si has always been a significant challenge for Si waste recycling. A novel application of electroslag remelting (ESR) refining has been developed to remove B and P for the purification and recovery of Si. In addition, industrial tests were performed to recover the diamond wire saw Si powder. The design principle is put forward for the Si alloy electroslag system. A new 35% CaO–30% CaF₂–17.5% Al₂O₃–17.5% SiO₂ electroslag applicable for Si alloy ESR is designed to meet both physical and impurity removal requirements. Furthermore, the conductivity (2.67 Ω–¹·cm–¹), density (2.97 g/cm³), and viscosity (0.05 Pa·s) meet the requirements of ESR. The dynamic refining process of Si alloy passing through the slag layer in the droplet form is the core of ESR refining, and it is found that more than 80% of B and P removal is achieved in the dynamic refining process of the droplet penetration slag. In order to understand the dynamic refining process, the mathematical model of droplet movement and impurity removal model are proposed to study the droplet movement behavior in slag and the competitive influence mechanism of multiple parameters on B removal efficiency during the dynamic refining process. Mathematical models and experimental results show that there is an ultimate velocity of droplet entry into the slag, which increases linearly with the growth of droplet size under the same slag condition. In addition, the specific surface area of the droplet plays a dominant role in the removal of B. The successful industrial experiments of Si alloy ESR prove that the design principle of the Si alloy electroslag system and the size control mechanism of Si alloy are feasible in this work. The removal efficiency of B and P reached 80 and 65%, respectively, within 30 min. It is also believed that ESR will have an application in purification and recovery of Si waste.

Influence of Bulk and Surface Interactions from Thick, Porous, Soil-based Substrates on the Spreading Behavior of Different Viscosity Oils

Crude oils and motor oils are commonly identified in oil spills on land. Controlling and understanding their flow both across and into land is of paramount importance to minimize spread and subsequent damage to the ecosystem. Spreading kinetics and surface energy studies were conducted with these oils over several realistic soil-based matrixes, consisting of topsoil (silt-dominant), sand, clay, and moisture. Spreading area through a 1.3 cm deep matrix was reduced with increased moisture content, densely packed matrixes, and higher viscosity oils. Initial contact angle (CA) measurements for all oils was typically lower on clay matrixes due to its sheet-like structure and high absorption capabilities. Individual droplet penetration took longer at lower MC in direct contradiction to bulk kinetics studies, suggesting different spreading behavior across the surface border. Low viscosity oils recorded the highest lateral spreads, and incomplete wetting profiles were identified for most conditions tested. Importantly, dimensionless profiles of droplet diameter and CA with time did not conform to universal behavior, with statistically significant influences of matrix heterogeneity, oil viscosity, and ill-controlled surface roughness identified. Flow regimes of oil droplets instead conformed to vertical spreading through thick matrixes, and a delayed lateral spreading that occurred quite late into the total penetration time of the droplet. These findings, obtained from studying realistic soil-based matrixes, draws new conclusions regarding the important influences of matrix thickness, variable porosity, and chemical heterogeneity on fluid flow behavior. This new knowledge will assist in the development of future containment efforts surrounding oil spills.

A comparison of bioinspired slippery and superhydrophobic surfaces: Micro-droplet impact

Slippery lubricant impregnated surfaces (SLIPSs/LISs) exhibit remarkable features of repellency and droplet mobility to a broad range of complex fluids. Their performance in micro-droplet repellency has received less attention. In this study, the anti-wetting performance of SLIPSs in comparison to superhydrophobic surfaces (SHSs) is investigated for the micro-droplet impact on different textured surfaces. Different series of square-pillar arrays are modeled to consider the effect of surface morphology on droplet hydrodynamics. A multiphase numerical model in conjunction with an accurate contact angle method has been implemented to analyze details of three immiscible phases during the droplet impact on the SLIPS. Our findings revealed that on the SLIPS with a low-density micro-textured surface where the effect of lubricant is more significant, droplet repellency and mobility are improved compared to SHSs. It was illustrated that on the SLIPS, droplet pinning decreased significantly and in low Weber number cases where the effect of lubricant is more noticeable, partial bouncing occurred. It was also observed that slippery surfaces with a low-density of micro-pillars exhibit bouncing behavior, which indicated the repellency effect of lubricant in droplet hydrodynamics. Although micro-droplets failed to recoil at a higher Weber number (We≃160) on both the SHS and the SLIPS, droplet penetration within the micro-structured surface was considerably smaller on the SLIPS.

Reduced root water uptake of summer maize grown in water-repellent soils simulated by HYDRUS-1D

Soil water repellency (SWR) is an ubiquitous soil property, that has major effects on surface and subsurface water flow, soil erosion, and therefore also affects plant growth and development. Soil water repellency has been recently observed to decrease summer maize growth, especially when the initial persistence of soil water repellency was high. However, mechanics implicated in maize biomass limitations are still unclear due to limited field observations and measurements of plant water use. This research aims to explain the possible mechanisms that impede the growth of summer maize in water repellent soils by examining soil water content, soil water evaporation and root water uptake (RWU) and comparing the measurements to simulations using HYDRUS-1D. Data from five increasing levels of SWR (CK, WR1, WR2, WR3 and WR4) from a two-year experiment were used. The soil hydraulic parameters described with the van-Genuchten model were calibrated inversely based on the observed volumetric soil water content at 26, 47 and 68 days after sowing (DAS) in 2016 and validated by water content values on 33, 62 and 91 DAS in 2017. The results showed the daily and cumulative RWU values ranked in an order of CK > WR1 > WR2 > WR3 > WR4. The RWU rates and cumulative RWU decreased with an increase of initial water droplet penetration time (persistence), which indicated weaker RWU ability of summer maize in the water repellent treatments. Thirty days after sowing, higher evaporation was observed in water repellent soils compared to CK. Weak RWU of summer maize grown in the water repellent soils and strong soil water evaporation were found. This research demonstrates the possible mechanisms that impede summer maize growth in water repellent soils could include weak RWU and high evaporation.

Effects of Crop Protection Unmanned Aerial System Flight Speed, Height on Effective Spraying Width, Droplet Deposition and Penetration Rate, and Control Effect Analysis on Wheat Aphids, Powdery Mildew, and Head Blight

As a new type of crop protection machinery, the Crop Protection Unmanned Aerial System (CPUAS) has developed rapidly and been widely used in China; currently, how to use the CPUAS scientifically has become a top priority. However, the relationships between the operating parameters of the CPUAS and the effective spraying width (ESW), droplet distribution characteristics, and control effects of insect pests and diseases are not clear yet. Therefore, three levels of flight speed (FS) as 3, 4, and 5 m/s, three levels of flight height (FH) as 1.5, 2.0, and 2.5 m, and spraying volume 2.0 L/min experiments were carried out to investigate the effects of FS and FH on the ESW, droplet deposition uniformity (DDU), and droplet penetration rate (DPR) by using an electric single-rotor CPUAS CE20. Based on the obtained results, combined with the insect pests and diseases occurrence agronomic laws, the optimal operation parameters of the CPUAS were selected to control the wheat aphids, powdery mildew, and head blight. The results showed that the ESW of CE20 was not consistent, the maximum value was 5.78 m, and the minimum one was 2.51 m. The FS had a highly significant impact on ESW (p = 0.0033 < 0.01), while the FH and the interaction between FS and FH had no significant impact on ESW. The coefficients of variation (CV) of the droplet deposition were between 23.3% and 34.4%, which meant good deposition uniformity. The FH (p = 0.0019) and the interaction between FS and FH (p = 0.02) had significant impacts on the DDU. The control effects on aphids were 78.71% (1 day), 84.88% (3 days), and 90.42% (7 days), the control effects on powdery mildew were 77.17% (7 days) and 82.83% (14 days), and the control effect on head blight was 88.32% (20 days). This study proved that by the optimization of parameters and the combination of agronomy, good control effects for insect pests and diseases could be achieved by the CPUAS. The research results would provide some technical supports for CPUAS application.

Application of transparent microperforated panels to acrylic partitions for desktop use: A case study by prototyping.

There are various measures currently in place to prevent the spread of coronavirus (COVID-19); however, in some cases, these can have an adverse effect on the acoustic environment in buildings. For example, transparent acrylic partitions are often used in eating establishments, meeting rooms, offices, etc., to prevent droplet infection. However, acrylic partitions are acoustically reflective; therefore, reflected sounds may cause acoustic problems such as difficulties in conversation or the leakage of conversation. In this study, we performed a prototyping of transparent acrylic partitions to which a microperforated panel (MPP) was applied for sound absorption while maintaining transparency. The proposed partition is a triple-leaf acrylic partition with a single acrylic sheet without holes between two MPP sheets, as including a hole-free panel is important to prevent possible droplet penetration. The sound absorption characteristics were investigated by measuring the sound absorption in a reverberation room. As the original prototype showed sound absorption characteristics with a gentle peak and low values due to the openings on the periphery, it was modified by closing the openings on the top and sides. The sound absorption performance was improved to some extent when the top and sides were closed, although there remains the possibility of further improvement. For this study, only the sound absorption characteristics were examined in the prototype experiments. The effects during actual use will be the subject of future study.

The Motion of Strawberry Leaves in an Air-Assisted Spray Field and its Influence on Droplet Deposition

HighlightsA visualization method for the motion of strawberry leaves in an air-assisted spray field is proposed.Strawberry leaves showed two motion states in different critical velocity ranges of the sprayer airflow.The airflow instability and the turbulence effect are considered important factors for the leaf vibrations.A strawberry leaf azimuth angle in the range of 90° to 270° can provide good deposition with smaller droplets.Abstract. The reasonable motion of crop plants in an air-assisted spray field can improve droplet deposition. Therefore, this study focuses on the motion of strawberry leaves and the droplet deposition mechanism in an air-assisted spray field. First, this study proposes a descriptive method for strawberry leaf motion in an air-assisted spray field and clarifies the important influence of strawberry leaf motion on droplet deposition. Second, an experiment was performed on the motion and droplet capture of single strawberry leaves in multi-position postures in an air-assisted spray field. The results showed that the leaves had two motion states (i.e., low amplitude with low frequency and high amplitude with high frequency) at different airflow velocities and inclination angles, and the critical airflow velocity corresponding to the two motion states was determined to be 8.7 m s-1. When the azimuth angle of the strawberry leaves is in the range of 90° to 270°, a reasonable inclination angle of the airflow and the high frequency and high amplitude vibration state of the leaves driven by the airflow will provide good deposition and canopy penetration of droplets with smaller diameters. Keywords: Air-assisted spray field, Droplet deposition, Motion, Spray, Strawberry leaves.

Droplet impacting a superhydrophobic mesh array: Effect of liquid properties

For numerous applications in microfluidic engineering, material science, and drug production, droplets of desired size and distribution are generated through liquid impingement on a perforated substrate. The dynamic process of droplet impact, spread, retraction, penetration, jet formation, and fragmentation into satellite droplets is simulated in a droplet impacting a mesh array configuration using an advanced lattice-Boltzmann method. The Weber number and Ohnesorge number are found to significantly influence the dynamics and outcomes, which can be explained by a qualitative and quantitative analysis based on the force and energy balance.

Lattice Boltzmann simulation of near/supercritical CO2 flow featuring a crossover formulation of the equation of state

In this work, we have incorporated a crossover equation of state into the pseudopotential multiphase Lattice Boltzmann Model (LBM) to improve the prediction of thermodynamic properties of fluids and their flow in near-critical and supercritical regions. Modeling carbon dioxide (CO2) properties in these regions is of increasing interest for industrial processes such as CO2 storage and heat transfer where CO2 is used as a working fluid. Despite the importance of accurately modeling near-critical and supercritical fluids, popular classical cubic equations of state (EoS) are not accurate. The proposed crossover EoS is a proven hybrid equation which uses the original classical EoS far from the critical point where it is valid, and near the critical point, it asymptotically switches to using non-analytic scaling laws. It also transforms into the ideal gas EoS as the density approaches zero. In order to demonstrate the validity and versatility of the crossover approach in the prediction accuracy of LBM in near-critical flows, this formulation was incorporated into the Peng-Robinson (P-R) EoS. First, 2D static droplets of CO2 and water at vapor-liquid equilibrium were modeled using both P-R EoS and its crossover formulation, and the numerically predicted results were then compared against the experimental data. The results demonstrate that the model accuracy in representing the thermodynamic behavior of the fluid in near-critical region is improved after adopting the crossover formulation with respect to the classical analytical EoS. The crossover P-R EoS was further applied to study several two-phase CO2 flows in mini-channels at near-critical temperatures. The flow patterns showed a good qualitative agreement with the experimental data in the near-critical region. The study is further extended to multi-component multiphase systems, specifically to water droplet penetration into porous media filled with CO2.

Fast-ion-induced secondary ion emission from submicron droplet surfaces studied using a new coincidence technique with forward-scattered projectiles.

A mass spectrometric study of secondary ions emitted from droplet surfaces by MeV-energy heavy ion impact was performed to investigate fast-ion-induced molecular reaction processes on liquid surfaces. Herein, a new coincidence technique was developed between secondary ions and scattered projectile ions at a small forward angle. The advantages of this technique were demonstrated by measurement of the collision between 4-MeV C3+ and ethanol droplets. Secondary ion emission probabilities were obtained directly from the coincidence data. Notably, this technique enabled positive fragment ions that had not been identified in previous measurements to be observed by suppressing the strong background originating from gas-phase molecules more than 104-fold. H+, H3O+, C2H5 +, and C2H5O+ were found to be produced as major positive fragment ions, in addition to minor fragments H2 +, C2H3 +, and CH2OH+. Production of these ions suggests that competition between rapid hydrogen ion emission from multiply ionized states and intermolecular proton transfer accompanied by fragmentation through protonated ethanol occurs after fast heavy-ion collisions. Clarification of the positive fragment ions also revealed the characteristic features of negative ions. Negative ions were realized to exhibit higher degrees of fragmentation and reactivity compared with positive ions. Furthermore, the energy loss by forward-scattered ions during droplet penetration was used to evaluate the target thickness at a submicron level. Variations in secondary ion yield, mass distribution, and kinetic energies depending on the penetration length were observed below 1 µm. These results highlight the unknown mechanism of these "submicron effects" observed in secondary ion emission processes as a new phenomenon.

Liquid droplet imbibition into a thin coating layer: Direct pore-scale modeling and experimental observations

In order to control ink droplet movement into the printing-paper layer, a set of pore-scale two-phase flow simulations were performed. The high-resolution three-dimensional pore space of the paper was obtained using focused ion beam scanning electron microscopy (FIB-SEM). Solving Navier-Stokes equations yielded details about dynamic movement of a droplet into the layer. To evaluate simulation results, for the first time, confocal laser microscopy imaging technique was integrated into a FIB-SEM chamber. Doing so, high resolution imaging of the droplet penetration inside paper was conducted and computed volume of penetrated ink at final stage was compared to the imaged volume. The ink penetration and spreading extent showed a good agreement with simulation results. Therefore, the developed simulation case was further investigated to study impact of liquid contact angle, real ink properties, and droplet arrival velocity on paper surface on final print quality. A faster penetration into the paper coating was observed for smaller equilibrium contact angles; meanwhile, more radial wicking was observed. In case of velocity of impact, higher velocity caused creation of irregular shapes of the ink footprint on paper surface. In addition to that, higher velocity caused ink splash which consequently created satellite droplets and lowered the print quality. Comparing ink-like liquid (representing real ink liquid properties) with water, water moves faster than ink-like liquid into the paper. This is mainly due to the higher viscosity and lower surface tension of the ink-like liquid.

Flow visualization of an N95 respirator with and without an exhalation valve using schlieren imaging and light scattering.

This work demonstrates the qualitative fluid flow characteristics of a standard N95 respirator with and without an exhalation valve. Schlieren imaging was used to compare an adult male breathing through an N95 respirator with and without a valve. The schlieren imaging technique showed the flow of warm air passing through these respirators but did not provide information about droplet penetration. For this, strategic lighting of fog droplets was used with a mannequin head to visualize the penetration of droplets through both masks. The mannequin exhaled with a realistic flow rate and velocity that matched an adult male. The penetration of fog droplets was also visualized with a custom system that seals each respirator onto the end of a flow tube. Results of these qualitative experiments show that an N95 respirator without an exhalation valve is effective at blocking most droplets from penetrating through the mask material. Results also suggest that N95 respirators with exhalation valves are not appropriate as a source control strategy for reducing the proliferation of infectious diseases that spread via respiratory droplets.

Study of spontaneous mobility and imbibition of a liquid droplet in contact with fibrous porous media considering wettability effects

In this paper, droplet mobility and penetration into a fibrous porous medium are studied considering different physical and geometrical properties for the fibers. An in-depth insight into the droplet imbibition into the fibrous medium is beneficial for improving membrane products in different applications. Herein, a multiphase lattice Boltzmann method is employed as an efficient numerical algorithm for predicting the multiphase flow characteristics and the interfacial dynamics affected by the interaction between the droplet and fibrous substrates considered. This computational technique is validated by comparison of the present results obtained for different benchmark two-phase flow problems with those reported in the literature, which shows good agreement and confirms its accuracy and efficiency. Droplet spreading and penetration into the fibrous porous geometries are then studied considering various porous topologies, intrinsic contact angles, and fiber sizes. This study shows that the intrinsic contact angle has a great influence on the capillary pressure and, consequently, on the droplet imbibition into the porous medium. The droplet easily penetrates the porous substrate by decreasing the intrinsic contact angle of the fibers, and vice versa. It is also concluded that by coating the fibrous porous medium with a narrow layer of thin fibers, the surface resistance to liquid penetration significantly increases. The present results illustrate that the droplet size impacts the directional wicking ability of the fibrous porous structure used in this study. This property should be considered to produce appropriate two-layer membranes for different applications.

Powder bed 3D printing with quarry waste

With 3D printing, material consumption can be reduced: It allows to place material only where needed, therefore structurally optimized building parts or formworks can be printed. Currently this technique uses an epoxy based resin to glue layer by layer an inert sand bed. However, this material choice holds a large improvement potential from an environmental and health perspective. It was shown previously, that the organic glue, that releases unhealthy volatile organic compounds, can be replaced by a mineralic binder, namely a geopolymer. With geopolymers and alkali activated materials, the embodied energy can be reduced, especially when built from waste materials. In this study, we focus on the replacement of the sand, which is becoming a scarce resource. The waste from a local gneiss quarry in Ticino (Switzerland) could be a good alternative. The powder bed of the 3D printing is made of aggregates of crushed quarry waste mixed with an aluminosilicate powder. The printing liquid is an alkaline solution that activates the aluminosilicate and reacts to a geopolymer. Droplet penetration experiments on different powder mixes were performed to adjust the binder composition. With a custom built powder bed 3D printer, samples with varying compositions and porosities were printed and tested on compression. It could be shown that samples printed with quarry waste perform as well as samples printed with silica sand in terms of compression strength and accuracy. This new material system is promising: with 3D printing of geopolymers and quarry waste, we can combine the environmental benefits of a new building technique with a low carbon intense material. The application of this technique may help the sustainable development of the local quarry sector by consuming the volumes of waste that causes storing and ecological issues and keep small quarries running.

A laboratory-based study examining the properties of silk fabric to evaluate its potential as a protective barrier for personal protective equipment and as a functional material for face coverings during the COVID-19 pandemic.

The worldwide shortage of single-use N95 respirators and surgical masks due to the COVID-19 pandemic has forced many health care personnel to use their existing equipment for as long as possible. In many cases, workers cover respirators with available masks in an attempt to extend their effectiveness against the virus. Due to low mask supplies, many people instead are using face coverings improvised from common fabrics. Our goal was to determine what fabrics would be most effective in both practices. Under laboratory conditions, we examined the hydrophobicity of fabrics (cotton, polyester, silk), as measured by their resistance to the penetration of small and aerosolized water droplets, an important transmission avenue for the virus causing COVID-19. We also examined the breathability of these fabrics and their ability to maintain hydrophobicity despite undergoing repeated cleaning. Laboratory-based tests were conducted when fabrics were fashioned as an overlaying barrier for respirators and when constructed as face coverings. When used as material in these two situations, silk was more effective at impeding the penetration and absorption of droplets due to its greater hydrophobicity relative to other tested fabrics. We found that silk face coverings repelled droplets in spray tests as well as disposable single-use surgical masks, and silk face coverings have the added advantage over masks such that they can be sterilized for immediate reuse. We show that silk is a hydrophobic barrier to droplets, can be more breathable than other fabrics that trap humidity, and are re-useable via cleaning. We suggest that silk can serve as an effective material for making hydrophobic barriers that protect respirators, and silk can now be tested under clinical conditions to verify its efficacy for this function. Although respirators are still the most appropriate form of protection, silk face coverings possess properties that make them capable of repelling droplets.

Rheological properties of carboxymethyl hydroxypropyl cellulose and its application in high quality reactive dye inkjet printing on wool fabrics

In this paper, the effect of rheological properties of pretreatment solutions, using carboxymethyl hydroxypropyl cellulose (CMHPC), sodium carboxymethyl cellulose (CMC), and sodium alginate (SA) as thickeners, on inkjet printing performance of wool with reactive dye inks was examined. Rheological, FESEM, and thickness results showed that fabrics treated with CMHPC solution, which exhibited superior fluidity, dominant elasticity property, and the largest zero-shear viscosity, produced the most continuous films and the lowest fabric thickness. Optical microscopy and XPS analyses confirmed that when compared with SA and CMC treated fabrics, CMHPC treated fabric controlled the excessive spread and penetration of ink droplets at higher effectiveness and produced the highest color strength (K/S value) and sharpest edge. In contrast to this, SA solution exhibited the worst fluidity, the most obvious viscous behavior, and lowest zero-shear viscosity. This resulted in the most discontinuous film, highest fabric thickness, and worst printing performance. Furthermore, wettability analysis demonstrated that the film structure dependent on the rheological property was the main factor that affected the inkjet printing performance of wool fabrics. CMHPC treatment of wool fabric provides an environment-friendly method with lower CMHPC concentration, less urea consumption, and shorter steaming time for higher K/S value.

Lattice Boltzmann simulation of water droplet impacting a hydrophobic plate with a cylindrical pore

The dynamics of a water droplet impacting on a hydrophobic plate with a cylindrical pore is captured by a nonorthogonal multiple-relaxation-time lattice Boltzmann method. Three distinctive regimes of droplet penetration behaviors: hanging, total crossing, and continuous dripping are found. A phase diagram is constructed for the different regimes, with the phase boundaries determined by the balance among the droplet dynamic pressure, capillary pressure, and viscous drag.