Air Pockets Research Articles

Diagnostic dilemma – Ovarian dermoid cysts presenting with uncommon complications and a rare association

Mature cystic teratomas, also known as dermoid cysts, are commonly encountered ovarian tumors accounting for up to 10–25% of all ovarian neoplasms. Mostly asymptomatic and incidentally detected, they may present with associated complications such as torsion, rupture, malignant transformation, and infection. Fistulization of ovarian cysts into the bowel is a rare complication and occurs in cases of infection or malignant transformation. We present a rare case of an infected dermoid cyst with co-existing endometriosis and fistulization into the rectum in a 35-year-old female. The patient presented with fever, pain, and history of infertility. This article highlights the important differential diagnosis to be considered in a multiloculated ovarian cyst containing fat and pockets of air.

A rare case of spontaneous giant pneumorrachis presenting with cauda equina syndrome: a case report.

Pneumorrachis is presence of air in the epidural space. It could be the result of trauma, barotrauma, iatrogenic or spontaneous. The pneumorrachis per se is an underdiagnosed entity as most of the patients are asymptomatic or have subclinical symptoms. The spontaneous occurrence of pneumorrachis has been reported in literature but giant spontaneous occurrence causing cauda equina syndrome has not been reported so far. We report a case of 56-year-old male patient who came to our OPD on wheelchair with complains of difficulty in walking for 6 months with dribbling of urine for 2 months with on and off back pain. His perianal sensation was reduced with absent voluntary anal contraction. Imaging revealed giant air pockets in the spinal canal of L5-S1 extending upto L4-L5. It was managed surgically wherein laminectomy without fusion was done. The patient responded well to the treatment. There are many causes of pneumorrachis described in literature. Most of the cases of pneumorrachis are asymptomatic and incidentally diagnosed. With the improvement in radio-diagnostic modalities, the diagnosis of pneumorrachis can be easily established. When symptomatic, they can be managed conservatively. Those presenting with neurological deficit may require surgical intervention or other invasive intervention.

Stirrer design for improving fluidization of cohesive powder: A time-resolved X-ray study

Stirring has been recognized in the literature as a promising technique for facilitating fluidization of cohesive powders, via inputting additional energy to counteract interparticle forces. However, the influence of operating conditions and stirrer configurations on flow behaviour remains largely unknown, which impedes the practical implementation of stirred fluidization. Utilizing X-ray imaging, this research demonstrates that stirring enhances fluidization in cohesive micron-silica powder (Sauter mean diameter ▪) by collapsing the powder packing structure, and transitioning channeling beds into bubbling states. Comb-like configurations featuring fewer stirrers and blades, placed in the bottom region, have shown to be highly effective. Excessive stirring can lead to air pockets and a compacted phase of particles on the column walls, undermining the interaction between particles and stirrers. Additionally, the experiments show that maximizing the sweeping coverage, employing complex asymmetrical configurations, and avoiding tortuous gas pathways are preferable.

Fast droplets impacting liquid layer under a small angle: a numerical analysis of experimental observations

In presence of a strong wind above a liquid surface, liquid droplets get accelerated and eventually hit the interface with a high speed under a small angle. Experimental studies demonstrate that such droplets may escape the initial crater and either get broken into secondary droplets in the air, or protrude along the interface, leaving behind agitated surface with entrapped bubbles. Here we aim at reproducing the observed phenomena in a numerical model based on Volume of Fluid technique using Basilisk package. On a flat interface, the impacting droplets partially escape the crater and get broken in front of it within the range of impact angles from 15° to 45°, in agreement to the experiments and simple theoretical considerations. In presence of waves, the escaping droplets fly into the air but, being adhered to the crater, get stretched and broken into secondary droplets. For smaller angles, the droplets escape the crater and glide along the interface. The gliding droplet creates a chain of small craters in its wake. The rims between the craters may grow and get scattered into secondary droplets. Large liquid viscosity and small thickness of the liquid layer suppress the growth of the craters and secondary entrainment. Bubble entrapment during such impacts most likely occurs due to crater collapse with trapping air inside. However, such air pockets are not formed systematically in the present model. This discrepancy requires further investigation.

Thermal behavior of flexible and breathable sandwich fibrous polyethylene glycol (PEG) encapsulations

Textiles incorporating phase change material have attracted increasing attention due to their temperature regulating function. Although a great progress has been made in the development of phase change material textiles, it has been found that the loading amount of phase change materials is limited by other final properties. Recently, we have proposed a sandwich fibrous phase change material encapsulation with a relatively high phase change material loading amount, which is a multi-layer fabric structure containing phase change material. However, the breathability of sandwich fibrous phase change material encapsulation should be improved because there is no path for air to penetrate through. In this work, the sandwich fibrous phase change material encapsulation structure with polyethylene glycol as phase change material is modified by introducing different air pockets in the thermal function layer ranging from 19% to 64%. The leakage phenomenon, phase transition behavior, thermal energy storage, breathability, T-history and practicality of the breathable sandwich fibrous phase change material encapsulations are investigated. As a result, the maximum polyethylene glycol loading amount of the phase change materials pocket is 83 wt%, and there is no leakage of polyethylene glycol during working time. The overall enthalpy value of the breathable sandwich fibrous phase change material encapsulation ranges from 27 J/g to 48 J/g. The optimal air permeability and water vapor resistance of the breathable sandwich fibrous phase change material encapsulation is 9 mm/s under 100 Pa and 34.5 m2 Pa W−1. Furthermore, the heterogeneous heat transfer through the breathable sandwich fibrous phase change material encapsulation is found due to the complicated thermal resistances of the hybrid thermal functional layer. In addition, for breathable sandwich fibrous phase change material encapsulation, the flexibility, hydrophobicity, self-cleaning property, abrasion resistance, and stability after water immersion are found. We believe the research has a great potential in various applications related to phase change material.

Symmetries in Dyck paths with air pockets

Symmetries in Dyck paths with air pockets

Liquid Marbles and Drops on Superhydrophobic Surfaces: Interfacial Aspects and Dynamics of Formation: A Review.

Liquid marbles (LMs) are droplets encapsulated with powders presenting varied roughness and wettability. These LMs have garnered a lot of attention due to their dual properties of leakage-free and quick transport on both solid and liquid surfaces. These droplets are in a Cassie-Baxter wetting state sitting on both roughness and air pockets existing between particles. They are also reminiscent of the state of a drop on a superhydrophobic (SH) surface. In this review, LMs and bare droplets on SH surfaces are comparatively investigated in terms of two aspects: interfacial and dynamical. LMs present a fascinating class of soft matter due to their superior interfacial activity and their remarkable stability. Inherently hydrophobic powders form stable LMs by simple rolling; however, particles with defined morphologies and chemistries contribute to the varied stability of LMs. The factors contributing to this interesting robustness with respect to bare droplets are then identified by tests of stability such as evaporation and compression. Next, the dynamics of the impact of a drop on a hydrophobic powder bed to form LMs is studied vis-à̀-vis that of drop impact on flat surfaces. The knowledge from drop impact phenomena on flat surfaces is used to build and complement insights to that of drop impact on powder surfaces. The maximum spread of the drop is empirically understood in terms of dimensionless numbers, and their drawbacks are highlighted. Various stages of drop impact-spreading, retraction and rebound, splashing, and final outcome-are systematically explored on both solid and hard surfaces. The implications of crater formation and energy dissipations are discussed in the case of granular beds. While the drop impact on solid surfaces is extensively reviewed, deep interpretation of the drop impact on granular surfaces needs to be improved. Additionally, the applications of each step in the sequence of drop impact phenomena on both substrates are also identified. Next, the criterion for the formation of peculiar jammed LMs was examined. Finally, the challenges and possible future perspectives are envisaged.

Exploring the air impacts on the state development of pipe flow using the smooth particle hydrodynamic method

Abstract It is widely recognized that the water flow in pipes can be affected by trapped air pockets. However, the underlying air–water interactions of free flow with non-jacking downstream of the pipe are rarely investigated. There are no studies at this time that clearly elucidate the differences in pipe flow between the vacuum and the presence of air in the free flow case. To this end, the smoothed particle hydrodynamics (SPH) method is applied to study the air–water hydraulic dynamics in the pipe under free flow. We perform SPH simulations in several different scenarios and find that (i) the SPH method is competent to simulate both single- and two-phase flows in the pipe due to its outstanding advantages in capturing complex interfaces; (ii) only when the upstream water level is higher than the top of the pipe inlet, and the water level in the pipe rises to the top of the pipe due to air resistance, can a full pipe flow be formed; and (iii) the presence of air can cause the water to form a full pipe flow, causing a siphon-like effect that promotes pipe drainage. These results provide insights into the underlying complex air–water hydraulic properties in pipe flows.

Toward Advanced Superomniphobicity: Hierarchical Insights from Serif-T Nanostructures to Microscale Wrinkles.

Developing a superomniphobic surface that exceeds the static and dynamic repellency observed in nature's springtails for various liquids presents a significant challenge in the realm of surface and interface science. However, progress in this field has been particularly limited when dealing with low-surface-tension liquids. This is because dynamic repellency values are typically at least 2 orders of magnitude lower than those observed with water droplets. Our study introduces an innovative hierarchical topography demonstrating exceptional dynamic repellency to low-surface-tension liquids. Inspired by the structural advantages found in springtails, we achieve a static contact angle of >160° and the complete rebound of droplet impact with a Weber number (We) of ∼104 using ethanol. These results surpass all existing benchmarks that have been reported thus far, including those of natural surfaces. The key insight from our research is the vital role of the microscale air pocket size, governed by wrinkle wavelength, in both static and dynamic repellency. Additionally, nanoscale air pockets within serif-T nanostructures prove to be essential for achieving omniphobicity. Our investigations into the wetting dynamics of ethanol droplets further reveal aspects such as the reduction in contact time and the occurrence of a fragmentation phenomenon beyond We ∼ 350, which has not been previously observed.

Study on the Dependence between Surface Topography and Icephobic Behavior of Ni–Cu–P Ternary Coatings

Unpredictable ice accretion and accumulation phenomena could lead to serious problems and even disastrous accidents. Applying icephobic coatings onto the engineering surfaces could be an effective ice protection method. The icephobicity could be mainly affected by several material strategies, such as wettability, surface topography and surface toughness, etc. Herein, several topographical surfaces (Ni–Cu–P coatings prepared on 304 stainless steel using electroless deposition) are critically investigated to understand the role of surface topography in affecting icephobic performances, including anti‐icing and deicing aspects. The freezing delay tests show that rougher surfaces contribute to longer icing delay in anti‐icing. The ice adhesion strength results indicate that rougher surfaces lead to a more mechanical interlock ice and increase the ice adhesion strength between the ice–solid interfaces. The electrothermal deicing tests indicate that the rough voids introduce large thermal resistance and impede heat conduction, resulting in the increase in detachment duration and energy input in deicing. The rough asperity could introduce air pockets at the surface interfaces, which leads to the difficulty of droplet phase transition. The rough structure also increases the mechanical interlock as well as the thermal resistance and impedes the heat conduction, which deteriorates the deicing ability.

Directional motion of water droplets enhances anti-icing failure of structural superhydrophobic surfaces

Preventing ice formation on solid surfaces is a crucial concern in various applications, such as aircraft de-icing and protecting electrical transmission cables. One approach to combat ice or frost formation involves the fabrication of superhydrophobic surfaces with micro- or nanostructures. However, some research suggests that the effectiveness of these superhydrophobic surfaces in preventing ice formation may be compromised under conditions of high humidity and low temperatures. Many researchers attribute the resistance of the wetting transition from the Cassie-Baxter state to the Wenzel state on superhydrophobic surfaces to Laplace pressure difference. However, according to molecular dynamics simulations and physical experiments, we find that the impact of Laplace pressure difference depends on the relative size of water droplets and air pockets on the structure. If the size of water droplets is smaller than the characteristic length of the air pockets, directional motion due to Laplace pressure difference and van der Waals force leads to water droplet aggregation and accelerates the ice formation and failure of anti-icing measures. Therefore, our research offers significant insights into the mechanical mechanisms that contribute to the failure of anti-icing techniques on structural superhydrophobic surfaces. This understanding is critical for the design of effective anti-icing or icephobic surfaces.

Air entrapment modelling during pipe filling based on SWMM

The paper proposes a novel methodology to locate and quantify entrapped air pockets created during pipe-filling events often found in intermittent water supply systems. Different filling conditions were tested in an experimental pipe with a high point. Measurements were taken and video recordings were carried out to assess air pocket volumes for different air release conditions at the downstream end of the pipe. The stochastic nature of air pocket creation resulted in varying air volumes. A new numerical model capable of simulating the air pocket creation, dragging and entrainment has been proposed. The new model, AirSWMM, was implemented as an extension of the Stormwater Management Model (SWMM) with stochasticity of air pocket formation reproduced by simulations with different air entrainment rates. The obtained numerical results show that the proposed model, even though based on a single-phase one-dimensional flow, can accurately locate and approximately quantify the entrapped air pocket volumes.

Multiscale air entrainment in wave-in-deck loads

Since entrapped air directly affects the properties of wave impact loads, it has long been unclear whether an air cushioning or entrapped-air amplifying effect exists. Wave-in-deck impacts are innovatively divided into four types based on the air-entrapped scale and characteristics of loads, namely, direct impacts, wave impacts with large or small air pockets (several metres to dozens of metres), and wave impacts with minute bubble plumes (tens of microns to several millimetres). In this study, a systematic study of multiscale air entrapment when waves impact a flat deck is conducted. After volume averaging, the temporal and spatial closure terms are rationally modelled to develop a multiscale air-entrapped wave impact model that couples the compression and expansion properties of large air pockets with the mean hydrodynamic properties of unsteady, nonuniform bubble plumes at a single acceptable grid scale. The high aeration and disordered bubble plume field, which the model successfully captured, as well as the impulsive pressure, have been validated for the typical dam-break impact problem. The results demonstrate that the model is capable of simulating air cavities entrapped in the initial moment of wave impact on the deck and the minute bubble plumes formed by the subsequent breakup, which offers a plausible new explanation for the investigation of the complicated mechanism of multiscale air-entrapped impact.

The study on the self-cleaning property of hydrophobic polydimethylsiloxane/nano-CaCO3 coating

<p>Dust depositions always degrade the building’s value due to the growth of mold and fungi. Manual cleaning is required to clean the building glass frequently which is time-consuming and costly. Self-cleaning coating is an effective and practical way to reduce dust accumulation. Using the sol-gel method, this study synthesized the self-cleaning polydimethylsiloxane (PDMS)/nano-calcium carbonate (CaCO<sub>3</sub>) coating. The coating recorded the water contact angle (WCA) of 99.5° ± 0.5°, indicating the hydrophobic property. The embedded nanoparticles create air pockets that reduce the adhesion between water droplets and glass surface. The hydrophobic coated glass showed the self-cleaning effect where the coating achieves a low dust haze of about 32% at the sliding angle 25°. The water contact angle (WCA) of the coating system degrades to 98.2° ± 1.2°, indicating the coated glass can maintain its hydrophobic property in the real environment after 1 month of outdoor exposure. In comparison, the bare glass showed large dust haze value above 50% due to the dust accumulation impact.</p>

Development of wet adhesion of honeybee arolium incorporated polygonal structure with three-phase composite interfaces

Inspired by the dynamic wet adhesive systems in nature, various artificial adhesive surfaces have been developed but still face different challenges. Crucially, the theoretical mechanics of wet adhesives has never been sufficiently revealed. Here, we develop a novel adhesive mechanism for governing wet adhesion and investigate the biological models of honeybee arolium for reproducing the natural wet adhesive systems. Micro-nano structures of honeybee arolium and arolium-prints were observed by Cryogenic scanning electron microscopy (Cryo-SEM), and the air pockets were found in the contact interface notably. Subsequently, the adhesive models with a three-phase composite interface (including air pockets, liquid secretion, and hexagonal frames of arolium), were formed to analyze the wet adhesion of honeybee arolium. The results of theoretical calculations and experiments indicated an enhanced adhesive mechanism of the honeybee by liquid self-sucking effects and air-embolism effects. Under these effects, normal and shear adhesion can be adjusted by controlling the proportion of liquid secretion and air pockets in the contact zone. Notably, the air-embolism effects contribute to the optimal coupling of smaller normal adhesion with greater shear adhesion, which is beneficial for the high stride frequency of honeybees. These works can provide a fresh perspective on the development of bio-inspired wet adhesive surfaces.

Multifunctional Microcavity Surfaces for Robust Capture and Direct Rapid Sampling of Concentrated Analytes

Evaporation patterns of liquid droplets containing nanoparticles or colloids have extensive applications in diagnostics and printing. Controlling these patterns by studying the evaporation behavior of colloidal droplets on surfaces is important for enhancing sensing platforms. In this study, A liquid‐repellent microcavity surface is introduced to robustly capture deposited analytic particles. The proposed microcavity surface maintains stable air pockets for liquid repellency and strong pinning for the spatial stabilization of the evaporating droplet, thereby resulting in a coffee‐ring concentration. This microcavity surface also acts as a “microcontainer” for the deposited particles, thereby protecting them against external damage. To demonstrate the multifaceted capabilities of microcavity surfaces, further comparison is done of three different surface structures, planar, micropillared, and that with microcavities in a hexagonal arrangement, by analyzing their evaporation dynamics and dried deposit patterns. The microcavity surface exhibits superior particle capture, thereby revealing its applicability in on‐site testing. Using the direct rapid sampling of analytical materials, the potential of the fabricated microcavity surface for point‐of‐care testing is demonstrated. The proposed microcavity surfaces suggest new avenues for the development of more robust and sensitive sensing platforms.

Congested Shallow Water Model: Trapped Air Pockets Modeling

Congested Shallow Water Model: Trapped Air Pockets Modeling

Two kinds of partial Motzkin paths with air pockets

Two kinds of partial Motzkin paths with air pockets

Tuning the Wettability of a High-Strength Aluminum Alloy Using a Picosecond Laser and Stearic Acid Coating

Imitating microstructures found in nature—such as lotus leaves and Namib beetles—is revolutionary in the field of surface science. Low-energy surfaces, when combined with different topographies, create different wetting states. Understanding the correlation between microstructure geometry and the behavior of water droplets is key to varying the contact angles on a low-energy surface. Here, a picosecond laser was used to modify the microtexture of aluminum alloy surfaces. Various microstructures were formed on the same surface, including the Laser-Induced Periodic Surface Structure (LIPSS), dual micro/nano hierarchical structures, and periodic arrays of a micropattern structure. Coating these microstructures with stearic acid was found to contribute to decreasing surface energy. The 92% fraction of the laser-machined to non-machined surface, when associated with different microgroove depths, created the capacity to form a superhydrophobic surface. Water droplets on a modified surface were transferred from hydrophilic at the Wenzel state to hydrophobic at the Cassie–Baxter state to a superhydrophobic state at microgroove depths ranging between 2.50 μm to 0.3 μm. The air pockets trapped in the microgrooves and nanocavities were found to subsidize the initiation of the composite interface underneath the water droplet.

Study on the Transient Flow Characteristics of a Hump Water Pipeline Based on the Random Distribution of Bubbles

Aiming at establishing the transient flow characteristics of gas–liquid two-phase flow in high-undulation water pipelines, based on the bubble distribution law measured using physical tests, the bubble distribution law function was input into the hump-pipe fluid domain model, and CFD numerical simulation was carried out for different flow rates and different air contents. The CLSVOF two-phase flow model and the RNG k-ε turbulence model were used to analyze the flow pattern evolution and pressure pulsation propagation in the process of gas–liquid two-phase flow through a hump pipe. The results show that the bubble size has a lognormal distribution, the equivalent diameter is between 3 mm and 10 mm, and the evolution of the flow pattern in the hump pipe is complex and violent. In the horizontal pipe section, there are three main flow patterns: bubble flow, wavy flow and segment plug flow. In the vertical pipe, there are two main flow patterns, slug flow and churning flow, and the flow pattern is affected by the flow rate and the air content rate. When air bubbles or air pockets in the pipeline flow through a certain area, this leads to a steep increase and decrease in the pressure pulsation amplitude in the region, and the pressure fluctuation is extremely frequent. Compared with the water flow rate, the air content is the main factor affecting the relative pressure pulsation amplitude under the condition of a 0.15-air content operating mode, which is generally approximately two to six times that of the 0-air content operating mode. The results of the research should facilitate the prediction of stagnant gas pipeline system bursts and water hammer protection, providing a theoretical basis and calculation parameters.