Air Entrapment Research Articles

Flow Test of Self Compacting Concrete using V-Funnel Test

Abstract: This paper gives a review on Self Compacting Concrete (SCC) to be made using various Mineral Admixtures and Fibres. In current scenario of construction industries due to demand in the construction of large and complex structures, which often leads to difficult concreting conditions. When large quantity of heavy reinforcement is to be placed in a reinforced concrete (RC) member, it is difficult to ensure fully compacted without voids or honeycombs. Compaction by manual or by mechanical vibratos is very difficult in this situation. That leads to the invention of new type of concrete named as selfcompacting concrete (SCC). This type of concrete flows easily around the reinforcement and into all corners of the formwork. Self- compacting concrete describes a concrete with the ability to compact itself only by means of its own weight without the requirement of vibration. Self –compacting concrete also known as Self-consolidating Concrete or Self Compacting High Performance Concrete. It is very fluid and can pass around abstractions and fill all the nooks and corners without the risk of either mortar or other ingredients of concrete separating out, at the same time there are no entrapped air or rock pockets. This type of concrete mixture does not require any compaction and is saves time, labour and energy. This review paper explains the utilization of fibres and various mineral admixtures in the properties of Self Compacting Concrete. The Benefits and Uses of SSC are discussed in this paper and Self-Compacting Concrete is compared with Cement Concrete. A V-Funnel is used to measure the flowability of concrete, and cost of Manufacturing a V-Funnel using Mild steel and Stainless Steel is estimated.

Experimental investigation into the effects of air pockets on wave-in-deck loads of offshore structures

In this paper, air entrapment during slamming is an investigation subjected to an experimental method of inquiry, analysed alongside a theoretical approach obtained from previous attempts to address similar matters. The experiment consisted of assembling three different sizes and depths of artificially created pockets underneath the 1:75 deck model of a 76 m × 76 m prototype to encourage air entrapment and study how this entrapped air affects local and global loads. A parametric study is ultimately conducted on the geometry of the pocket, altering area and depth to observe the response to the pressure. Air entrapment effects were observed to reduce the magnitudes of impact pressure inside the pocket while slightly altering the force time histories in x and z-directions. Force magnitudes for global forces are significantly close to the smooth deck results. However, horizontal force data are slightly higher than their corresponding smooth deck due to additional surfaces inside the pocket. In addition, a parametric study of the depth and size of the pocket reveals that pocket depth is the dominant parameter that affects the impact pressure inside a pocket.

Determination of properties and environmental impact due to the inclusion of cigarette fibers in mortar: a new solution to mitigate the CB pollution.

Cigarette butts generated are one of the major sources of total solid waste production and lead to environmental issues. This article has the objective of evaluating the effects of cellulose acetate microfibers (CAFs) sourced from discarded cigarette filters (CFs) as fiber reinforcement on the physico-mechanical properties and thermal conductivity of cementitious materials. To do so, mortar samples were prepared using different incorporated quantities of fibers (0.5, 1, 1.5, 2, 2.5, and 5% compared to the quantity of sand added to the mixture) and subjected to different tests to characterize the influence of CAFs on the microstructure of elaborated materials, considering the changes in workability time, compressive strength, flexural strength, density, water absorption, and microstructural analysis. Furthermore, the life cycle assessment (LCA) of mortar mixes in terms of CO2 emissions is made. The results revealed that the increasing percentages of CAFs reduced the dry density and compressive strength, by approximately 1.62-51% and 37-69.64%, respectively, and a notable enhancement of insulation characteristics by about 5-47.5% was achieved. Microstructure analysis confirmed the experimental investigation and revealed that adding more than 1% of fibers resulted in a significantly low unit weight with greater entrapped air content. The studies prove the possibility of recycling cigarette butts for insulating cementitious matrix. In addition, applying mortar containing acetate cellulose fibers is recognized as a more environmentally friendly mixture in terms of reducing CO2 emissions and could participate significantly in the achievement of SDGs.

Correlation between the severity of lung involvement and nasal mucociliary clearance time and acute phase biomarkers in patients with COVID-19

Objectives: The aim of this research was to evaluate the correlation between the increased nasal mucociliary clearance time (NMCT) and chest computed tomography severity scores (CT-SS) and acute phase biomarkers in patients diagnosed with coronavirus disease 2019 (COVID-19) pneumonia. Patients and Methods: A total of 116 hospitalized patients were included in the prospective study between November 2021 and June 2022. For the measurement of the NMCT, all patients underwent the saccharin test. The patients were separated into two groups: Group 1, which included 53 patients (28 females, 25 males; mean age: 50.1±13.2 years; range, 19 to 75 years) with an NMCT of 7-13 min, and Group 2, comprising of 63 patients (32 females, 31 males; mean age: 52.3±12.1 years; range, 30 to 82 years) with an NMCT of 14-21 min. The CT-SS was adapted from a previous method including ground-glass opacity, interstitial opacity, and air entrapment and was used to express the severity and rate of involvement of COVID-19 pneumonia. Results: The mean CT-SS was 3.8±1.6 in Group 1 and significantly higher in Group 2 with 6.2±2.0 (p<0.001). In addition, a strong positive correlation was determined between the NMCT and CT-SS (r=0.711). The mean lung lobe involvement was 3.6±1.5 in Group 1 and 4.8±0.5 in Group 2, and the difference was statistically significant (p<0.001). The mean ferritin levels showed a statistically significant difference at 244.6±146.9 mg/L in Group 1 and 436.5±449.1 mg/L in Group 2 (p=0.038). Conclusion: The saccharin clearance test is not routinely used in clinical practice but with the lights of our study’s results increased NMCT results correlates with pneumonia severity scores in CT and it may be useful in the prediction of prognosis of pneumonia in COVID-19 patients.

Evaluation of lung function in a German single center cohort of young patients with sickle cell disease using EIT and standard techniques.

Sickle cell disease (SCD) is a very common autosomal recessive hemoglobinopathy leading to multiple pulmonary complications that are closely associated with mortality. The pathophysiology of chronic pulmonary involvement is not yet fully understood and no specific therapies are available. The aim of this cross-sectional study was to characterize the lung function of children and young adolescents with SCD in a German single-center cohort and to extend conventional lung function testing by the use of a new imaging method. We performed spirometry and body plethysmography in 35 children and young adults with hemoglobin SS, SC, S/β-thalassemia as well as 50 controls. These data were compared with clinical characteristics and typical laboratory parameters of hemolysis and disease activity in SCD. To identify lung inhomogeneities, for example due to atelectasis, hyperinflation, air trapping or vascular occlusions, we used the promising new method of electrical impedance tomography (EIT) and calculated global inhomogeneity indices. Lung function of patients with SCD was significantly reduced compared to that of healthy controls. When the result was found to be pathological, the most commonly observed type of breathing disorder was classified as restrictive. Laboratory parameters showed typical features of SCD including decreased levels of hemoglobin and hematocrit and elevated levels of leucocytes, platelets, lactate dehydrogenase and total bilirubin. However, there was no correlation between blood values and reduced lung function. Electrical impedance tomography (EIT) revealed no abnormalities in SCD patients compared to healthy controls. In particular, we were unable to demonstrate any regional inhomogeneities in lung ventilation. In our study, SCD patients showed impaired lung function, with a relevant percentage of patients suffering from restrictive breathing disorder. Signs of obstruction could not be detected. Electrical impedance tomography (EIT) measurements revealed no unevenness that would suggest air entrapment, blockage of blood vessels, excessive inflation, obstruction, or other forms of lung disease. Additionally, the reduction in lung function observed in SCD patients was not related to the disease severity or laboratory test results.

An experimental study on the role of different void removal mechanisms in VBO processing of advanced thermoplastic composites

The current study is focused on understanding the role of different void removal mechanisms in VBO processing of advanced thermoplastic composites. For this purpose, two commercially available Carbon/Poly-Ether-Ketone-Ketone (C/PEKK) tape materials were evaluated, distinct in morphologies, such as surface roughness and fiber-matrix distribution, and physical characteristics, mainly the presence of volatiles. The VBO consolidation results proved that the void reduction and removal mechanisms varied depending on the tape material. However, restricting the void reduction mechanism to dissolution and diffusion alone. Depending on the tape material, a significant difference in the consolidation dwell time was observed to achieve <1% void content parts. Thus, indicating that despite the tapes having the same polymer matrix, they differ in their diffusion behavior. The difference in the times required for consolidation may be due to the following. Firstly, the diffusion coefficients may be different for the two tapes. Although the matrix material in both tapes is PEKK, the exact formulation is unknown. Secondly, the volume of gases, which comprises entrapped air and the volatiles that evaporate during the process, that need to be removed maybe be different.

A model for the consolidation of hybrid textiles considering air entrapment, dissolution and diffusion

A model for the consolidation of hybrid textiles considering air entrapment, dissolution and diffusion

Clinical Consequences of Incidental Durotomy during Full-Endoscopic Lumbar Decompression Surgery in Relation to Intraoperative Epidural Pressure Measurements

Background: Seizures, neurological deficits, bradycardia, and, in the worst cases, cardiac arrest may occur following incidental durotomy during routine lumbar endoscopy. Therefore, we set out to measure the intraoperative epidural pressure during lumbar endoscopic decompression surgery. Methods: We conducted a retrospective observational cohort study to obtain intraoperative epidural measurements with an epidural catheter-pressure transducer assembly through the spinal endoscope on 15 patients who underwent lumbar endoscopic decompression of symptomatic lumbar herniated discs and spinal stenosis. The endoscopic interlaminar technique was employed. Results: There were six (40.0%) female and nine (60.0%) male patients aged 49.0667 ± 11.31034, ranging from 36 to 72 years, with an average follow-up of 35.15 ± 12.48 months. Three of the fifteen patients had seizures with durotomy and one of these three had intracranial air on their postoperative brain CT. Another patient developed spinal headaches and diplopia on postoperative day one when her deteriorating neurological function was investigated with a brain computed tomography (CT) scan, showing an intraventricular hemorrhage consistent with a Fisher Grade IV subarachnoid hemorrhage. A CT angiogram did not show any abnormalities. Pressure recordings in the epidural space in nine patients ranged from 20 to 29 mm Hg with a mean of 24.33 mm Hg. Conclusion: Most incidental durotomies encountered during lumbar interlaminar endoscopy can be managed without formal repair and supportive care measures. The intradural spread of irrigation fluid and intraoperatively used drugs and air entrapment through an unrecognized durotomy should be suspected if patients deteriorate in the recovery room. Ascending paralysis may cause nausea, vomiting, upper and lower motor neuron symptoms, cranial nerve palsies, hypotension, bradycardia, and respiratory and cardiac arrest. The recovery team should be prepared to manage these complications.

A theory of porous media for unsaturated soils with immobile air

The Theory of Porous Media (TPM) has served as a reliable theory to deduce governing equations for unsaturated soils. In most works, the unsaturated soil is considered as a three-phase medium composed of air, water and solid. This neglects effects caused by the presence of residual water and/or entrapped (immobile) air attached to the particles. In this work, a set of governing equations for unsaturated soils with residual water and entrapped air is deduced. A mass transfer mechanism between the free air and the entrapped air is considered. The present work focuses only on the entrapped air attached to the particles (immobile air), and therefore it is assumed to have the same intrinsic velocity as the solid. This assumption allows to keep the same number of independent kinematic variables as in conventional three-phase theories. The performance of the theory is examined in simulations of water retention curves subjected to suction cycles, as well as in the dynamic analysis of a centrifuge test on a dam subjected to earthquake loading.

Towards development of sustainable metallic superhydrophobic materials

In the present study, an environment friendly, scalable, and cost-effective approach is proposed, combining thermo-mechanical and microwave-assisted hydrothermal processing techniques, resulting in the augmentation of nanoscale structures on metallic surfaces. The thermo-mechanical processing of the aluminium alloy performed at different strain rates resulted in significant grain refinement (∼ 1 µm for processed and ∼ 30 µm for unprocessed samples). After hydrothermal treatment, highly dense and networked nanostructured morphology was evoked by refined grains. Post silanization, samples exhibited high contact angle (θs > 155°) with a low tilt angle (θt < 10°) and CAH (< 5°). The low adhesion with water (∼ 16 µN) for the processed sample (∼ 50 μN for unprocessed) with utmost refined grains is attributed to the high interfacial energy of Cassie state (EC−B>1.0J) due to effective entrapment of air. The processed samples were highly de-wetting and mechanically resilient owing to the strong negative capillary pressure (PC > 1100 kPa) generated by highly dense networked nanostructures. As a result of thermo-mechanical processing, samples displayed higher resilience to abrasion, simulated rain, and long-term immersion tests with low tilt angles (θt < 10°) and CAH (< 5 °). This paper provides a practical approach to achieve anti-wetting surfaces in various industrial settings.

Influence of HPDC Process Parameters on the Microstructure of EC Electromotor Housing

The mechanical properties of high-pressure die-casted parts are directly influenced by their microstructure. This article aims to evaluate the effect of the fast-shot speed on the structural component and overall microstructure for two geometrically different castings. The material used during experimental works is commonly known as the AlSi9Cu3(Fe) alloy. For experimental purposes, numerical simulations, microstructural and EDS analysis, the DAS index, length of eutectic Si plates and more were implemented. The simulations have shown the possibility of air entrapment in the filling chamber. Oxides, and consequently microporosity, were localized, which led to the selection of critical points of the casts for further observation and evaluation. With the use of the optical/scanning microscope and microhardness evaluation, the fast-shot speed value of 3.6 m.s−1 was selected as the most advantageous.

Experimental validation of a new adaptable LCM mold filling software

Resin Transfer Molding (RTM) is a manufacturing process for fiber reinforced polymer composites where dry fibers are placed inside a mold and resin is injected under pressure. During mold design, filling simulations can study different manufacturing concepts (i.e. placement of injection gates and vents) to guarantee complete filling of the part and avoid air entrapment where flow fronts converge. In this work, a novel software tool LCMsim, which was implemented by the authors, is benchmarked against other tools and real-world flow experiments. Its development was driven by two ideas: Easy-of-use for the mold engineer and maximum flexibility for the researcher. Two experiments were used for validation. In the first, zones with different preform properties were present and in the second, race-tracking was enforced. Flow fronts from LCMsim and experiment agree with 7% error and simulated flow fronts from LCMsim and the commercially available software PAM-RTM agree with 3% error.

Hydrodynamics of Non‐Equilibrium Soil Water Retention

AbstractWater retention in soil exhibits diverse phenomena, including suction‐saturation hysteresis, non‐unique air entrapment at zero suction and negative suction under partial saturations. The constancy of suction after a long rest can be broken by relatively minor mechanical or hydraulic agitations such as low‐amplitude wetting cycles—this fact is here being related to metastable states that differ from the true equilibrium. The complete suction‐saturation relationships are thus being recovered using non‐equilibrium Landau's hydrodynamic theory and Onsager's reciprocity principles. Equilibrium suction does not pertain to hysteresis, yet can be approached through small amplitude agitations over long duration. Conditions for rate independence are being described, while rate‐dependency are also accommodated and illustrated. Finally, it is shown that the new non‐equilibrium theory retains the rigorously derived equilibrium result of the effective stress of partially saturated soils.

Numerical investigation of air cushioning in the impact of micro-droplet under electrostatic fields

Air cushioning widely occurs when a droplet impacts onto a solid or fluid surface at low velocity, which is mediated by the lubrication pressure of a thin air layer. Such air cushioning phenomena for micro-sized droplets bear important implications for precision coating and inkjet printing. In this study, we investigate numerically the air cushioning in the micro-sized droplets of various sizes impacting on a solid surface based on the volume of fluid method as implemented in the OpenFOAM framework. We find that the critical impact speed for bouncing on the air cushion increases as the droplet radius decreases, while the Weber number remains in a narrow range from 1 to 4. The scaling law of the critical impact speed for bouncing is derived by balancing the lubrication pressure of the air cushion with the capillary pressure and droplet inertia. The impact mode transforms from bouncing to wetting with an electric field. A group of phase diagrams of the electric Bond number vs the Weber number is presented for various droplet sizes. The diagrams are consistent with the scaling law of the critical electric field for the wetting-without-bubble mode. The findings provide insights for applications based on micro-droplet deposition, such as inkjet/electrohydrodynamic printing and spray coating, to avoid the adverse effect of air cushioning or air entrapment.

Trauma-related pneumopericardium

Trauma-related pneumopericardium (TRPP) is the collection of air in the pericardial space secondary to trauma, potentially leading to tension pneumopericardium (TPP) in which the entrapment of air generates sufficient pressure to compromise cardiac output leading to a life-threatening cardiac tamponade and circulatory failure. We aim to classify the diagnostic and therapeutic approaches of TRPP and the causes of the subsequent development of TPP. A computer-based search of all published reports on TRPP in the medical literature from database inception to March 2020, on MEDLINE, Ovid, and Scopus; analyzing the data regarding initial status at presentation, extent of injuries, diagnostic and treatment measures with the intention to have an understanding of the clinical behavior and management outcomes of TRPP. The search identified 84 published case reports of 105 patients with TRPP. In conclusion, TRPP leading to TPP is described in the literature as a condition that involves a young male who is subjected to blunt trauma, most commonly in a motor vehicle collision, presenting as a polytrauma patient in a state of shock and low systolic blood pressure, or possibly in cardiac arrest. In addition, he might have a tracheobronchial injury with or without pneumothorax or pneumomediastinum and might require mechanical ventilation.

Numerical analysis of air entrapment during water droplet impact on a substrate

As a liquid droplet impact on a substrate, it spreads flattens, and air may become trapped between the droplet and the substrate. This trapped air first evolves into an air film, which passes through many stages before eventually becoming an air bubble through retraction, contraction, toroid creation, pinching off, and so forth. The droplet cools while spreading across the substrate and finally freezes to create a splat. In most thermal spray coating applications, this phenomena is seen in the individual droplet solidification. The major purpose of this research is to develop an OpenFOAM solution that can model the effect of molten droplets on solid surfaces using free surface evolution. The PIMPLE algorithm, which is used in this solution, combines the PISO (Pressure Implicit with Splitting of Operators) and SIMPLE (Semi Implicit Method for Pressure-Linked Equations) approaches. In this approach, pressure–velocity equations are resolved, and the continuous surface flow model is used to simulate the surface tension force. Furthermore, the solution incorporates the dynamic contact angle. An enthalpy-based formulation that takes solidification into account is used to simulate the energy equation. The solver is validated with the aid of the available experimental results. Hydrodynamics can be used to properly simulate the various stages of air entrapment.

Phase Field Modeling of Air Entrapment in Binary Droplet Impact with Solidification Microstructure Formation

A novel numerical model was developed to investigate air entrapment in binary droplet impact with solidification microstructure formation under practical plasma spraying conditions. The evolving liquid–gas interface was tracked by the explicit finite difference solution to the Cahn–Hilliard equation, coupled with the Navier–Stokes equations. Another diffuse interface model was invoked to trace solid–liquid and grain–grain boundaries. The model was discretized using an explicit finite difference method on a half-staggered grid. The velocity pressure coupling was decoupled with the projection method. The in-house code was written in Fortran and was run with the aid of the shared memory parallelism, OpenMP. The time duration over which gas compressibility matters was estimated. Typical cases with air entrapment were studied with the model. The effect of droplet porosity on air entrapment was probed into as well: the larger the porosity of a droplet, the bigger the trapped air bubble. The grain growth near the air bubble is skewed. Moreover, a case without air entrapment was also shown herein to stress that air bubbles could be suppressed or even eliminated in plasma spraying by adjusting the landing positions of successive droplets.

Numerical Water Impacts of 2D Hull Forms using Dynamic Overset Meshing

The phenomenon of slamming is often the critical design load for high-performance marine craft. Slamming involves the solid-fluid impact of a hull structure, resulting in large forces acting on the structure from the large volume of water displaced in a very short time frame. Due to its importance in the design and operation of marine craft, the impact of ship forms into water has been the focus of a significant body of literature. These studies have primarily focused on rigid shapes, so the effects of hydroelasticity have not been examined in detail. This paper presents a robust and practical methodology for simulating water impacts involving overset meshing and the Volume of Fluid (VOF) method using the Ansys Fluent 2021 R1 Computational Fluid Dynamics (CFD) solver. The framework involves a high resolution dynamic overset mesh attached to the body in a coarse static Cartesian background mesh. Results for a simple 2D wedge impact are compared to experimental and analytical results and a good agreement to the validation material is observed. A 2D transverse section based on the IMOCA60 racing yacht Banque Populaire VIII is then analysed to obtain impact force and pressures. Results capture the peaked pressure distributions characteristic of slamming, with possible effects of air entrapment. The methodology presented is applicable for designers of high-performance sailing craft to improve the prediction of hydrodynamic loading on their hull-form designs. The overset method can quickly and easily be applied to a number of different geometries and impact events with minor changes between models.

Energy dissipation in a rapid filling vertical pipe with trapped air

An energy-dissipation model is developed to simulate rapid filling having an entrapped air pocket within a vertical pipe. Both convective heat transfer and transient wall shear stresses are considered. The resulting predictions are compared both to those obtained via a conventional empirical polytropic model and to experimental data. The comprehensive model accurately reproduces the experimental pressure oscillations. Results reveal that the dynamic behaviour of air pockets in all tested cases approaches a purely adiabatic process over the first two oscillations, but also that the pressure variation then gradually evolves to an isothermal variation. Moreover, the high air temperatures predicted in the numerical simulations account for the observed phenomenon of white mist in the pipe as well as the notably hot pipe wall. Significantly, the conventional empirical polytropic model associated with the adiabatic assumption for the gas phase was sufficient to reproduce the pressures and temperatures during the first two oscillations.

Influence of wetting behavior on the morphology of droplet impacts onto dry-patterned micro-structured surfaces

The influence of surface roughness, especially regularly patterned micro-structures on the physical outcomes of droplet impacts, is far from fully understood. In order to get a deeper insight into the physics of the impact phenomena, a systematic experimental study of the morphology on regularly patterned micro-structured surfaces has been carried out. The used structures with different dimensions were grooves and pillars with a square cross section. With the help of plasma activation and plasma polymerization processes, the surface wettability was modified independently from the surface structure and material. Two different test fluids were used, namely, distilled water and isopropanol, impacting with various impact energies onto the patterned surface samples. For a better characterization of the impact process, high-speed images from three different perspectives have been acquired synchronously. Due to the transparent surface material, the bottom perspective using a total internal reflection configuration was able to visualize air entrapment inside the surface structure. To the authors' knowledge, such images are not available in the literature, yet. The outcomes have been qualitatively investigated, summarized, and compared. A dependency of the outcomes on the impact energy, the surface wettability, and the structure dimensions could be clearly shown. In general, increasing impact energy will promote the tendency of splashing. However, roughness features cannot only trigger splashing, but can also inhibit it, for example, crown splashing. Moreover, reproducible arrangements of air entrapment inside the structure could be found, which was addressed by the authors as “cookie” and “button” due to their appearance.