Spreading Diameter Research Articles

The spreading and sliding characteristics of droplet impingement on an inclined hydrophobic surface at low Weber numbers

Droplet sliding after impingement on an inclined superhydrophobic surface has very broad applications, but the investigations of this variable process are surprisingly lacking in the literature. In this paper, the spreading and sliding characteristics of a water droplet impinging on an inclined hydrophobic surface at low Weber numbers (We≲ 50) are investigated via a numerical approach. The influences of surface inclined angle α, impact velocity, and droplet diameter on droplet spreading diameter and maximum spreading diameter (Ds and Ds_max), sliding lengths of droplet, droplet leading and trailing edges (Ld, Llea and Ltra) are thoroughly examined. Results show that droplet displays markedly distinct behaviors when α≥ 60° as the maximum spreading diameter is noticeably larger and droplet oscillation becomes stronger and more unstable, which are contributed from the accumulated liquid mass at droplet head associated with the drastic growth of the tangential inertial force. However, the instability at α≥ 60° disappears when We≥ 40, resulting from the liquid mass at droplet head dominating the sliding process, which demonstrates that droplet motion at a high inclined angle is primarily determined by droplet leading edge. The nondimensionalized maximum spreading diameter (Ds_max∗) is found to scale with the normal Weber number (WeN) according to a power law (Ds_max∗∝WeNα1), and a universal scaling law of Ld_total∗∝WeT0.6 between the nondimensionalized total sliding length (Ld_total∗) and the tangential Weber number (WeT) is discovered. The relationship between the four distinct post-impingement regimes identified in this work and the Weber and Bond numbers are presented and explained. These results offer fresh insight into the currently insufficient understanding of droplet sliding process on inclined hydrophobic surfaces.

Water-Droplet Impact and Sliding Behaviors on Slippery Surfaces with Various Weber Numbers and Surface Inclinations

The dynamic behaviors of water droplets on a slippery surface are significant to practical anti-icing applications. Herein, the impact and sliding behavior of water droplets on lubricant-infused surfaces (LISs) were investigated with a high-speed camera. LISs were prepared by infusing perfluoropolyether oils into anodized porous surfaces. The results show that the maximum spreading diameter and retraction velocity of the impact droplet increased with the We number. For LIS-100, the spreading factor at 2.5 ms increased from 2.00 to 3.88 with We increasing from 30 to 267. Low-viscosity lubricant facilitated the retraction speed and rebound of droplet impact on the surface, while high-viscosity lubricant contributed to the lubricant stability of the LIS. Additionally, high inclination angle (θ) facilitated the rapid shedding of water droplets on the surface. The velocity increased rapidly from 1.04 to 4.66 mm/s with θ increasing from 15° to 45°. The LIS prepared with low-viscosity lubricant had a high sliding velocity, and the sliding velocity of water droplets on LIS-100 was about seven times faster than that on LIS-104. This work reveals the impacting law of water droplets on LISs and provides useful information for the design of LISs under drop impact conditions.

Dynamical behaviors of aluminum droplets impinging on horizontal and inclined surfaces

Aluminum (Al) droplets collide with the wall of the combustion chamber in a solid rocket motor at different angles of incidence and velocities, which exhibit rebounding, splashing, and other behaviors. It increases the loss of two-phase flow to degrade the performance of the engine and poses a challenge to the thermal protection system. In this study, an experimental system in which molten Al droplets impact the walls of the chamber is designed. The size of the Al droplets produced by the generator ranged from 120 μm to 2000 μm while their speeds of impact ranged from 0.85 m/s to 9 m/s. This was used to examine the process of impact of Al droplets on flat and inclined walls. The residence time and spreading diameter of the droplets were quantified to reveal their mechanism of collision. Their empirical correlations were obtained by regressing the experimental data, and the predictive error of the model was within 20% of the experimental values. Furthermore, a theoretical model was developed to analyze energy distribution during the collision between the droplets and the wall. It showed that the effect of viscous dissipation energy on droplet flow was negligibly small, but the adhesion energy of the droplet increased significantly with its initial energy. In addition, the dimensionless sliding distance was S≈8 when the tangential Weber number was greater than 90, where this was related to the high surface tension of the Al droplets. The results here provide a theoretical basis for the design of thermal protection system of solid rocket motors.

Effect of mixture flowability on strength and fiber distribution of Ultra High-Performance Fiber Reinforced Concrete

The uniformity of distribution and the orientation factor of steel fibers are crucial parameters that determine the strength and uniformity of properties of Ultra High-Performance Fiber Reinforced Concrete (UHPFRC). The paper considers the influence of flowability and the method of casting the concrete mixture on the strength and fracture energy in bending of UHPFRC. The flowability was determined by the spread diameter of the mixture from the Hägermann cone, which was 270, 300, and 350 mm. It was found that the compressive strength of UHPFRC increases from 142 to 155 MPa with an increase in the mixture spread diameter. The strength and fracture energy in bending of UHPFRC near the ends of the mold are on average 14.5 and 17.7% less than in the central part. A relationship has been established between the flexural strength of UHPFRC and the fracture energy as a function of the relative area of the fiber in the cross-section. The optimal flowability range of UHPFRC (270…290 mm) was established analytically and experimentally, in which there is no critical decrease in strength properties and the ability of the mixture to self-leveling is maintained. Negative effects were established when changing flowability, outside the specified range.

Impact of different organic and inorganic sources of nutrients on vegetative growth of marigold (<em>Tagetes erecta</em> L.) under agro-climatic conditions of Ajmer zone

The present investigation was conducted at Bhagwant University Ajmer, Rajasthan during the rabi season of years 2019-20 and 2020-21 to find out the combined application of different organic and inorganic sources of nutrients on growth behaviour of Marigold (Tagetes erecta L.) under Agro-climatic conditions of Ajmer Zone. Total ten treatments were used in Randomized Block Design (RBD) and replicated three times. The treatments namely T1- Control, T2- 100% RDF (N:P: K @ 120:80:60 kg/ha), T3-100% RDF + 25% VC, T4- 100% RDF + 25% FYM, T5- 75% RDF + FYM + Biofertilizers, T6- 75% RDF + VC + Biofertilizers, T7- 75% RDF + FYM + VC + Biofertilizers, T8- 50% RDF + FYM + VC + Biofertilizers, T9- 50% RDF + FYM + Biofertilizers and T10- 50% RDF + VC + Biofertilizers. Total 30 treatment combinations were formulated in present experiment. During the experimentation, observations were recorded on various growth characters like plant height, number of primary branches, number of secondary branches, plant spread and stem diameter at various successive stages of growth. Though, the maximum growth and flowering was found in T7- 75% RDF + FYM + VC + Biofertilizers as compared to T8- 50% RDF + FYM + VC + Biofertilizers.

Prospects for using amorphous ferromagnetic alloy microwire for reinforcement of cement mortar

Traditionally, fibers for fiber-reinforced concrete are made of metal, polypropylene, basalt or glass. На сегодняшний день для строительства актуально использование волокон с уникальными электрофизическими свойствами. The possibilities of using a microwire made of an amorphous ferromagnetic alloy based on cobalt with a shell of borosilicate glass in concrete technologies are studied in this paper. The influence of the content of fibers of different sizes (length 7 and 15 mm) on the rheological and physico-mechanical properties of the solution was established. The deterioration of the workability of mixtures and the average density of the composite with the introduction of the studied fiber is shown. It has been established that the spread diameter of the mortar mixture with a fiber content of 0.5...3.0 % by weight of Portland cement is reduced by 9.8...26.1% compared to the control composition. It is shown that the short fiber (7 mm) at the maximum content (3 %) leads to a more significant decrease in the average density (up to 9.6 %) compared to the long fiber (15 mm) of the same concentration (reduction is no more than 4 %). A positive effect on the flexural strength and crack resistance of the solution was established. The increment of flexural and compressive strength ranges from 1.11 to 1.54 and from 0.99 to 0.78 respectively with increasing fiber concentration. The presence of fiber in the composition of the solution allows you to increase the crack resistance from 0.098 to 0.164. The increase in the crack resistance coefficient for compositions with a fiber 7 mm long is 51...68 % and compositions with a fiber 15 mm long is 22...37 %. The possibility of using such microwire based on a ferromagnetic alloy for dispersed reinforcement of cement solutions opens up prospects for the creation of “smart” materials.

Lubricant Droplets Can Bounce on Wetted Cylinders

In this work, the droplet bounce phenomenon of polyalphaolefin, olive oil, silicone oil, and paraffin oil on wetted cylinders was reported. With a uniform oil film with a thickness of 0.06 mm formed on the cylinder, typical categories of spread, maximum, retract, deposit, and bounce existed. The ratio of the maximum spreading diameter and the initial diameter was negatively corrected with the viscosity due to the viscous resistance. The effect of tangential velocity from 0 m/s to 0.75 m/s on the spreading was investigated, which shows a strong promotion for it. The force analysis explained the mechanism of bouncing caused by the compressed air film, and oil droplets would bounce if the support force was larger than the combined force of gravity and inertia force. The findings in the work provide a basic understanding of droplets impact on wetted and rotating surfaces and design concepts for applications in modern industry.

An Experimental Investigation on Workability and Bleeding Behaviors of Cement Pastes Doped with Nano Titanium Oxide (n-TiO2) Nanoparticles and Fly Ash

In this study, the workability of cement-based grouts containing n-TiO2 nanoparticles and fly ash has been investigated experimentally. Several characteristic quantities (including, but not limited to, the marsh cone flow time, the mini slump spreading diameter and the plate cohesion meter value) have been measured for different percentages of these additives. The use of fly ash as a mineral additive has been found to result in improvements in terms of workability behavior as expected. Moreover, if nano titanium oxide is also used, an improvement can be obtained regarding the bleeding values for the cement-based grout mixes. Using such experimental data, a multi-layer perceptron artificial neural network model has been developed (5 neurons in the hidden layer of the network model have been developed using a total of 42 experimental data). 70% of the data employed in this model have been used for training, 15% for validation and 15% for the test phase. The results demonstrate that the arti- ficial neural network model can predict Marsh cone flow time, mini slump spreading diameter and plate cohesion meter values with an average error of 0.15%.

Droplet lift-off from hydrophobic surfaces from impact with soft-hydrogel spheres

Droplet impacts on superhydrophobic surfaces may result in complete bouncing, with the absence of contact hysteresis and viscous dissipation leading the droplet to fully rebound off the surface. This rebound usually happens in the retraction phase, when the droplet retracts back after reaching a maximum spread diameter. Here, we present experimental evidence of a bouncing phenomenon where a sessile droplet on a hydrophobic surface bounces off the surface in its spreading phase when a soft deformable hydrogel sphere axisymmetrically impacts the droplet. We term this as ‘Lift-Off’ and propose a simple force balance based on the deformation characteristics of the hydrogel sphere to explain the out-of-plane jump of the droplet during spreading. We observe three different impact regimes, and propose their dependency on a modified elastic ‘Mach’ number (Ma*) with Ma* ≈ 0.1 corresponding to the onset of lift-off. We also report on the unique acoustic signatures of lift-off cases, associated with the capture of air-bubbles through the air-borne retracting droplet rim. These results may have potential applications for drainage and surface cleaning, non-stick surface coating, industrial mixing and plant disease spreading.

Low thermal conductivity substrate accelerates droplet evaporation in transition boiling regime: An abnormal Leidenfrost phenomenon

We investigate droplet evaporation on heater surface with different thermal conductivities. The complete droplet evaporation curves are obtained using the phase change lattice Boltzmann model, including four regimes of film evaporation, nucleate boiling, transition and Leidenfrost. Three thermal conductivities of substrate heater (λs) are paid attention. We found that higher λs does not always accelerate droplet evaporation. In the regimes excluding transition regime and Leidenfrost regime, higher λs increases droplet evaporation rate. However, in transition regime, lower λs enhances droplet evaporation, explained by that lower λs triggers second contact of droplet and heater and decreases vapor film thickness underneath droplet. Detailed droplet characteristic features including droplet spreading diameter, projected diameter of suspended drop, and vapor thickness in transition boiling regime are investigated in detail. The droplet oscillation in vertical direction during transition boiling for low thermal conductivity heater is found numerically for the first time. We conclude that low thermal conductivity material is benefit for heat transfer improvement due to the triggering of second contact (TSC) between droplet and solid surface.

Experimental study on the slump-flow underwater for anti-washout concrete

The workability of underwater anti-washout concrete (UWC), especially the flowability in particular application environments, was always a critical and controversial issue. In this paper, a new test device and approach have been proposed to study the behavior of underwater flowability of UWC and establish a relationship with laboratory slump-flow tests. Further, the effects of different mix proportions, such as aggregates, superplasticizer (SP), water-cement ratio (W/C), anti-washout agents (AWAs) type and dosage, beside yield stress and plastic viscosity of UWC were investigated. The differences (Δd) between the spread diameter of the samples in air and underwater were compared. The results indicate that the flowability of concrete underwater is less than that in air, and it was proved that there is significant association between the yield stress and Δd. Also, various factors that affect the spread diameter difference are prioritized to optimize the rheological properties and limit the underwater flowability loss as much as possible. Combined with the Roussel's flow model and stress equilibrium differential equations, the theoretical formula of interpreting UWC's underwater flowability loss by yield stress was deduced, which can certify that the buoyancy underwater counteracts part of the gravity that keeps the UWC flowing freely and reduces its maneuverability. Additionally, an empirical formula of underwater spread diameter of UWC was proposed according to the variation law that the spread diameter difference decreases due to the increase of yield stress. Finally, the outcomes provided basic theoretical reference to filling capacity of UWC when casting underwater.

Binder Jetting Additive Manufacturing: Spreading and Permeation of Multiple Micron Droplets in Porous Media

AbstractThe penetrating behavior of binder droplets has a substantial effect on the dimensional correctness and strength of the manufactured components. In this article, a physical model and a mathematical model of multiphase flow are created, computationally computed, and experimentally validated to predict the spreading and penetration behavior of multi‐drop binder in a powder bed. The findings indicate: 1) The spreading diameter and penetration depth of the binder increase as the number of droplets grows. However, the size of the rise reduces as the number of droplets grows. 2) The binder is spread symmetrically in the powder bed, with greater saturation in the middle area than margins on both sides, and a higher saturation in the upper region than the lower. 3) Repeated drops of binder in various areas may improve the saturation of the peripheral region while ensuring that the core area is not oversaturated. 4) It is discovered that as the number of ink jet drops rises, the size of the sample grows, and the growth in sample size reduces with the number of ink jet drops. This paper's findings provide light on the mechanics behind light‐cured binder jet additive manufacturing.

Vegetative Growth, Yield and Quality of Broccoli As Influenced by Application of Gibberellic Acid

Field experiments on broccoli cv. ‘BARI Broccoli-1’ was carried out during two consecutive rabi seasons of 2014-15 and 2015-16 at the field of Plant Physiology Section of HRC, BARI. 30 days old seedlings were treated before transplanting by dipping their roots for 24 h in different concentrations of GA3 (Gibberellic acid) viz., 20, 40, 60, 80 and 100 ppm along with control (distilled water). The experiment was laid out in a Randomized complete block Design with three replications. GA3 concentrations significantly influenced the growth parameters, yield and yield attributes and quality parameters of broccoli. In regard to the average data of two years, GA3 @ 60 ppm gave the maximum leaf length (46.58 cm), spread diameter (52.38 cm), head circumference (38.2cm cm), head length (16.60 cm), head diameter (15.45 cm), primary and secondary head weight/plant (289.85 g and 192.80 g). The maximum head yield (18.82 t/ha in 2014-15 and 21.39 t/ha in 2015-16) with an average of 20.11 t/ha was recorded at GA3 @ 60 ppm followed by GA3 @ 40 ppm. Application of GA3 @ 60 ppm also produced the highest head compactness index (18.77 g/cm), maximum vitamin C (82.88 mg/100 g FW), vitamin A (601.90 IU/100 g FW) contents and the highest total soluble solid (10.10%). From the investigation it was also observed that application of more than 60 ppm GA3 reduced the yield attributes and yield of broccoli.
 Bangladesh J. Agril. Res. 45(3): 247-259, September 2020

Controlling post-impact dynamics of ferrofluid droplets with magnetic field

Preventing droplets from splashing after impacting a thin layer or liquid pool is crucial in reducing cross-contamination, the spread of pathogens, and rough surfaces in three-dimensional (3D) printing. In this article, we demonstrate that an external magnetic field can be useful to actively control the post-impact dynamics of ferrofluid droplets. A simplified lattice Boltzmann method (SLBM) is applied to simulate the flow field with lower computational cost. For the magnetic field, a self-correcting procedure is coupled with SLBM by setting a permanent magnet of desired magnetic field strength at any location of the computational domain. In this article, four different phenomena are simulated, including static contact angle, dynamic contact angle, splashing droplet on a thin layer, and falling droplet into a pool same liquid. From the first two examples, it is deduced that a vertical non-uniform magnetic field not only controls the spreading diameter and apex height but also the puffy shape appearing at droplet laterals. In examples three and four, even more intricate crown structures and wave propagation are successfully controlled with the help of a permanent magnet. It is also discovered that a magnetic field introduced at an optimal starting moment improves control and speeds up the whole procedure.

Influence of the Metal Surface Texture on the Possibility of Controlling the Phase Transition of Water Droplets in the Single-Phase Regime

We experimentally studied the influence of the texture of copper and steel surfaces on the possibility of controlling the phase transition of water droplets in the single-phase regime. The texture of metals was formed by polishing and grinding, which corresponded to the finishing treatment of heat transfer surfaces in cooling systems for energy-saturated equipment. The samples were studied by microscopy and profilometry. The texture was estimated by three-dimensional roughness parameters. It was found that, with a 2–2.5-fold increase in roughness, the wetting of copper deteriorates (the contact angle increases from 66° to 93°), whereas the wetting of steel improves (the contact angle decreases from 89° to 71°). It was experimentally proven that, among the two main factors that affect the spreading diameter (wetting and roughness), wetting is the most significant. A hypothesis was formulated regarding the reason for the increase in the contact angle of 7–10° and the drop in the decrease rate of the contact diameter during the transition from the pinning to the mixed stage of droplet evaporation. It was found that an increase in the surface area of 0.1% leads to an increase in the total droplet evaporation rate of 4–6.5%.

Dynamics of drops on hygroscopic ionic liquid aqueous solution-wetted porous surfaces

The impact dynamics of water drops on porous surfaces wetted by a hygroscopic ionic liquid aqueous solution are investigated. Firstly, to better illustrate the different dynamic characteristics of water drops on ionic liquid-wetted porous surfaces, it is compared with that on the dry and water-wetted porous surfaces. The results indicate that, the water drop barely penetrates on the dry porous surface at ambient temperature, but penetrate when the surface temperature is raised or the surface is pre-wetted. The maximum spreading and penetration of the droplet on the ionic liquid-wetted surface is larger and faster than that on the water-wetted surface. Then, the effect of the mass fraction of aqueous ionic liquid, impact velocity, porosity on the spreading and penetration is explored. The larger the mass fraction of aqueous ionic liquid on the porous surface, the faster the droplet spreading factor, height, and residual volume decrease. The effect of impact velocity is even more pronounced for the water droplets impacting on pure ionic liquid-wetted porous surfaces. A higher porosity contributes to a smaller spreading diameter but a larger volume decreasing rate on the wetted porous surface.

Dynamical behaviors of water drop impact on superhydrophobic surfaces with the macro-textured cavity

Drop impact on superhydrophobic surfaces (SHSs) is of significant importance to many engineering applications. Drop impact dynamics on micro-nano structured SHSs has been widely investigated, however, that on macro-textured SHSs is still lacking, especially the macro-textured cavities. In this work, water drops impact on rigid SHSs with or without cavities were experimentally investigated through a high-speed camera. We number (We = ρdu2/σ) is chosen to quantify the drop impact intensity. Compared to plane SHSs, the cavity with different geometries reduces both the maximum spreading diameter and the contact time, and leads to complex drop deformation with two times expanding process under higher We numbers. The maximum spreading ratios increase with We numbers and are scaled by a power-law with exponents of 0.20 for plane SHSs and 0.17 for cavity-textured SHSs. The dimensionless contact time on plane SHSs remains constant about 0.88, while that on the cavity-textured SHSs is about 0.82. Drop impact on SHSs with macro-textured cavities exhibits different behaviors, which anticipates to throw an insight into the applications of self-cleaning, anti-icing and so on.

Analysis of methods, equipment, and spread diameter ranges for self-leveling mortars

Analysis of methods, equipment, and spread diameter ranges for self-leveling mortars

Experimental and Numerical Investigation on the Dynamics of Impacting Droplet Spreading at Small Weber Numbers

The dynamic of droplet spreading on a free-slip surface was studied experimentally and numerically, with particularly interest in the impacts under relatively small droplet inertias (We≤30). Our experimental results and numerical predictions of dimensionless droplet maximum spreading diameter βmax agree well with those of Wildeman et al.’s widely-used model at We>30. The “1/2 rule” (i.e., approximately one half of the initial kinetic energy Ek0 finally transferred into surface energy) was found to break down at small Weber numbers (We≤30) and droplet height is non-negligible when the energy conservation approach is employed to estimate βmax. As We increases, surface energy and kinetic energy alternately dominates the energy budget. When the initial kinetic energy is comparable to the initial surface energy, competition between surface energy and kinetic energy finally results in the non-monotonic energy budget. In this case, gas viscous dissipation contributes the majority of the dissipated energy under relatively large Reynolds numbers. A practical model for estimating βmax under small Weber numbers (We≤30) was proposed by accounting for the influence of impact parameters on the energy budget and the droplet height. Good agreement was found between our model predictions and previous experiments.

Spreading and retraction of the concentric impact of a drop with a sessile drop of the same liquid: Effect of surface wettability

The concentric impact on a sessile drop is relevant in many applications, including spray coating and icing phenomena. Herein, the spreading and retraction phases yielded during the impact of a coaxial drop with a sessile drop on a solid substrate were empirically and analytically examined. We analyzed the effects of surface wettability on the impact outcomes utilizing five distinctive surfaces (i.e., smooth glass, aluminum, copper, Teflon, and coated glass). The results showed that the merged drop takes longer to attain its maximum spreading diameter at a relatively higher contact angle of the sessile drop with the solid surface. Furthermore, based on energy balance, a model for predicting the maximum spreading diameter of the drop with varying surface wettability was presented. This model considers the assumption of viscous energy loss during the merging of falling and sessile drops and at the maximum spreading diameter. Additionally, the maximum retraction height during the impact on the coated glass surface was investigated. Our model results matched well with the experimental data.