Formation Of Air Pockets Research Articles

The Conservation of a Painting. Case Study: Cornel Minişan, “Landscape from Caransebeş” (Oil on Canvas, 20th Century)

This paper presents a case study of the conservation of an oil painting produced by the Romanian inter-war painter Cornel Minisan in the 1930s One of the main problems of the art-work for which I had to find an appropriate solution, was the deformation of the painting's support. The painting on canvas was marouflaged in the past on a pressboard. The inapropriately executed intervention has led to the formation of air pockets between the canvas and the pressboard Another important issue in the conservation process was the cleaning of the art-work. Its entire surface was covered by a thick layer of adherent dirt In addition to the intervention on the painting's support and the cleaning, the conservation work undertaken entailed other interventions as well, all aimed at bringing the painting in a stable state of conservation and at the same time restoring its intended, aesthetically appropriate form.

Permeability of Aluminium Foams Produced by Replication Casting

The replication casting process is used for manufacturing open-pore aluminum foams with advanced performances, such as stability and repeatability of foam structure with porosity over 60%. A simple foam structure model based on the interaction between sodium chloride solid particles poorly wetted by melted aluminum, which leads to the formation of air pockets (or “air collars”), is proposed for the permeability of porous material. The equation for the minimum pore radius of replicated aluminum foam is derived. According to the proposed model, the main assumption of the permeability model consists in a concentration of flow resistance in a circular aperture of radius rmin. The permeability of aluminum open-pore foams is measured using transformer oil as the fluid, changing the fractions of initial sodium chloride. Measured values of minimum pore size are close to theoretically predicted ones regardless of the particle shape. The expression for the permeability of replicated aluminum foam derived on the basis of the “bottleneck” model of porous media agrees well with the experimental data. The obtained data can be applied for commercial filter cells and pneumatic silencers.

CFD 기반 유체충격 해석에서 공기 압축성 효과

This paper describes the air compressibility effect in the CFD simulation of water impact load prediction. In order to consider the air compressibility effect, two sets of governing equations are employed, namely the incompressible Navier-stokes equations and compressible Navier-Stokes equations that describe general compressible gas flow. In order to describe violent motion of free surface, volume-of-fluid method is utilized. The role of air compressibility is presented by the comparative study of water impact load obtained from two different air models, i.e. the compressible and incompressible air. For both cases, water is considered as incompressible media. Compressible air model shows oscillatory behavior of pressure on the solid surface that may attribute to the air-cushion effect. Incompressible air model showed no such oscillatory behavior in the pressure history. This study also showed that the CFD simulation can capture the formation of air pockets enclosed by water and solid surface, which may be the location where the air compressibility effect is dominant.

Effect of Different Aluminium Surface Treatments on Ice Adhesion Strength

Excessive ice accumulation on power network equipment can affect their integrity and cause damage with serious socioeconomic consequences. To mitigate that, de-icing techniques (mechanical or thermal) have been developed, but these techniques are often limited in their application and are generally expensive and time consuming. Recently, companies and research groups have focused on the development and application of icephobic coatings such as superhydrophobic materials intended to drastically reduce ice adhesion force on exposed equipments. The aim of this paper is the examine the influence of aluminium surface treatments on ice adhesion. Preparation of new and various aluminium surface treatments as well as the need to improve the knowledge of the mechanisms involved in ice adhesion are part of this research. Depending of the type of materials, surface roughness can either promote the formation of air pockets within pores or between coating surface asperities (low adhesion strength), or it can create ice mechanical anchoring if water partially or totally penetrates the porosity. Aluminium anodization using phosphoric acid was studied. Surface morphology was evaluated using scanning electron microscopy and measurements of ice adhesion strength were performed using a centrifuge technique. Based on these results, several surface treatments of aluminium have been considered including aluminium anodizing with partial Al2O3 etching followed by different sealing steps using hydrophobic polymer compounds such as polytetrafluoroethylene.

Experimental apparatus to test air trap valves

It is known that the presence of trapped air within water distribution pipes can lead to irregular operation or even damage to the distribution systems and their components. The presence of trapped air may occur while the pipes are being filled with water, or while the pumping systems are in operation. The formation of large air pockets can produce the water hammer phenomenon, the instability and the loss of pressure in the water distribution networks. As a result, it can overload the pumps, increase the consumption of electricity, and damage the pumping system. In order to avoid its formation, all of the trapped air should be removed through "air trap valves". In Brazil, manufacturers frequently have unreliable sizing charts, which cause malfunctioning of the "air trap valves". The result of these malfunctions causes accidents of substantial damage. The construction of a test facility will provide a foundation of technical information that will be used to help make decisions when designing a system of pipelines where "air trap valves" are used. To achieve this, all of the valve characteristics (geometric, mechanic, hydraulic and dynamic) should be determined. This paper aims to describe and analyze the experimental apparatus and test procedure to be used to test "air trap valves". The experimental apparatus and test facility will be located at the University of Campinas, Brazil at the College of Civil Engineering, Architecture, and Urbanism in the Hydraulics and Fluid Mechanics laboratory. The experimental apparatus will be comprised of various components (pumps, steel pipes, butterfly valves to control the discharge, flow meter and reservoirs) and instrumentation (pressure transducers, anemometer and proximity sensor). It should be emphasized that all theoretical and experimental procedures should be defined while taking into consideration flow parameters and fluid properties that influence the tests.

Physical Investigation of Discrete Air Pocket Migration and Release in CSO Storage Tunnels

Various rapid filling scenarios lead to the formation of large discrete air pockets in below ground storage tunnel systems. The release of trapped air pockets …

Roughness effects on contact angle measurements

We have developed a simple and economical procedure to demonstrate the effects of roughness and wetting fraction on the equilibrium contact angles of liquid droplets on solid surfaces. Contact angles for droplets placed on a rough surface, which wet only a portion of the surface, are larger than the contact angles of droplets formed by condensation of steam, which wet the surface more completely. These contact angle data facilitate assessments of changes in true surface area, due to surface roughening, as well as changes in the fractional contact areas of the water droplets, due to the formation of air pockets between the rough surface and the droplet.

Influence of Effective Particle Porosity on Vacuum Fluidized Bed Drying

A series of vacuum fluidized bed drying experiments was carried out employing particles with distinct effective porosities. The experiments showed that decreasing the operating pressure as well as increasing the operating temperature produces higher drying rates in both drying periods. In all cases, the enhancement of the drying rates was found to be more significant in the case of particles with higher effective porosities. It is concluded that lower operating pressures as well as higher operating temperatures help to reduce the formation of air pockets in the pores and postpone the onset of the pendular state, enhancing the capillary action and the drying rates.

Internal and external structure of pellets made in a rotary processor

The internal and external structure of pellets made in a rotary processor by the wet granulation technique was studied using the following techniques: helium pycnometry to determine the true density, krypton adsorption to determine the specific surface area, mercury porosimetry, and scanning electron microscopy. The results of the true density measurements, specific surface area determinations and mercury porosimetry led to the hypothesis that the pellets were open porous sponge structures. Mercury mainly intruded in the macropore range (pores with a radius between 7 and 0.05 μm). The pores and cavities were partially closed as spheronization went on leading to air pockets in the pellets. Scanning electron microscopic pictures provided visual support for the hypothesis that the pellets had a porous surface and that the pellets contained cavities, which could be closed resulting in the formation of air pockets. To reduce the pore volume and smooth the surface, the rotor speed should be high and the spheronization time should be long. The plastic properties of wetted microcrystalline cellulose promoted the smoothing of the surface.

Measurement of density and wetness in snow using time-domain reflectometry

Time-domain reflectometry (TDR) is widely used in soil physics to determine water content. Existing equipment and methods ran be adapted to measurements of snow wetness. The main advantages compared to other methods are flexibility in constructing sensors, minimal influence on snow cover during measurements and sensors can be multiplexed. We developed sensors suitable for continuous and non-continuous measurements of snow wetness and density, measured the apparent permittivity in different snow densities and snow types, and compared the measurements to existing mixing formulas for mixtures of snow and air. In dry snow, density was measured from 110 to 470 kg m−3. The residual error is 14 kg m −3 and the 95% confidence interval of our model is 3 kg m−3. To measure snow density and wetness continuously suitable sensors have been constructed. Their small size and high surface area to weight ratio minimizes their movement in the snowpack, except when they are exposed to intense solar radiation. Results show that changes in dry-snow density of less than 5 kgm−3 can be detected. Infiltration of even small amounts of water clearly shows up in the permittivity. At the surface of the snowpack, problems occur due to the formation of air pockets around the sensors during long-term measurements.

Measurement of density and wetness in snow using time-domain reflectometry

Time-domain reflectometry (TDR) is widely used in soil physics to determine water content. Existing equipment and methods ran be adapted to measurements of snow wetness. The main advantages compared to other methods are flexibility in constructing sensors, minimal influence on snow cover during measurements and sensors can be multiplexed. We developed sensors suitable for continuous and non-continuous measurements of snow wetness and density, measured the apparent permittivity in different snow densities and snow types, and compared the measurements to existing mixing formulas for mixtures of snow and air. In dry snow, density was measured from 110 to 470 kg m−3. The residual error is 14 kg m −3 and the 95% confidence interval of our model is 3 kg m−3. To measure snow density and wetness continuously suitable sensors have been constructed. Their small size and high surface area to weight ratio minimizes their movement in the snowpack, except when they are exposed to intense solar radiation. Results show that changes in dry-snow density of less than 5 kgm−3 can be detected. Infiltration of even small amounts of water clearly shows up in the permittivity. At the surface of the snowpack, problems occur due to the formation of air pockets around the sensors during long-term measurements.

Wetting and Melt Extraction Characteristics of ZrO2–Al2O3 Based Materials

A melt extraction technique has been used to produce fine fibers from three eutectic compositions in the systems of ZrO2‐Al2O3 (ZA), ZrO2‐Al2O3‐SiO2 (ZAS), and ZrO2‐Al2O3‐TiO2 (ZAT). The liquid surface tension of these ceramics was measured by a new method and estimated to be in the range of 400‐567 mJ/m2 at similar ∼2400°C. The wetting between Mo (the extraction wheel material) and liquid ceramics was found to be poor during transient wetting; however, fiber extraction was achieved due to the shear action induced by the wheel rotation. The difficulties in the extraction of ZA fibers at speeds of <1.5 m/s, and also the formation of air pockets on these fibers, are attributed to the poor wetting of the Mo wheel by the liquid ZA. In a wide range of wheel velocities, extracted fibers exhibited alternating sections of uniform diameter and Rayleigh waves, both being the largest for ZAS fibers at any speed. The Rayleigh wave dimensions varied considerably with speed whereas the dimensions of the uniform region of the fibers remained unchanged over the wide range of extraction speeds examined. The fiber dimensions are controlled by both surface tension and viscosity of the molten ceramics at the extraction temperature.

Effect of melt temperature on the formation of air pockets during splat quenching

The effect of melt temperature on the formation of air pockets at the contact surface of the ribbons was studied. An alloy with a melting point slightly higher than room temperature (320 K) was used and was heated to 353, 573 and 773 K, respectively, to investigate the thermal effect of the melt temperature on the gas. Under high casting velocity (20 ms−1) and extremely low melting temperature (353 K), the air pockets were slender and parallel to the casting direction. The liquid melts with a higher casting temperature (773 K) induced coarse air pockets at various casting velocities, and the air pockets were coarser than those induced by the pressure of the gas boundary layer only. The heat flow analysis showed that the local pressure of the entrapped gas, built up by the thermal effect and assuming constant volume, is far greater than the pressure by the gas-boundary layer effect. Thus the thermal effect of the liquid melt should be taken into account in the formation of air pockets during splat quenching.

Air Dynamics Through Filter Media During Air Scour

The dynamics of air motion through filter media under conditions of air scour alone, simultaneous air and subfluidization water flow and simultaneous air and fluidization water flow were studied. Particular combinations of simultaneous air and subfluidization water flows cause the formation and collapse of air pockets within the bed: termed Collapse‐Pulsing. This condition probably created significant abrasion between the filter media grains because the intensity of abrasion is related to the effective stresses between the grains and the magnitude of their relative movement. It is rationalized that collapsepulsing is the probable optimum condition for air scour. Three sands of effective sizes, 0.46 mm, 0.64 mm, and 0.88 mm, were experimentally studied and a simple empirical predictive equation for collapse‐pulsing was established. The equation is also shown to be valid for predicting the condition for a minimum loss of media during backwash. The equation could be used for the design of air scour systems t...

Fundamentals and Theory of Air Scour

An original theoretical analysis of the dynamics of air scour from a fundamental and microscopic viewpoint is presented. Concepts in soil mechanics and porous media hydraulics are combined to explain the complex flow patterns which emerge when air and water flow concurrently through porous media. An equation which predicts the formation and collapse of air pockets within the bed is developed by equating the air pressure within a bubble to the soil stresses in an active Rankine state plus the pore‐water pressures. This condition of collapse‐pulsing which occurs at particular combinations of simultaneous air and subfluidization water flows has been associated with the probable optimum condition for air scour. The theory compares well with four sets of experimental data collected on two different graded sands. The theoretical expression has been condensed into a simple design equation for practical application.

Growth of Mechanically Planted Nectarines Planted at Various Depths1

Abstract High-budded trees of nectarine [Prunus persica (L.) Batsch] that were mechanically planted with the bud union as a depth guide resulted in poorer growth when compared to those planted with the crown roots within 5 cm of the surface. Deeper-planted trees had smaller leaves and less total increase in trunk cross-sectional area, and were more susceptible to the formation of air pockets around their bases.

Processing Stripping Film Autoradiographs of Citrus Buds; Avoidance of Entrapped Air between Tissues and Developed Emulsion

Autoradiography was used on paraffin sections for investigating DNA synthesis in vegetative and flower buds of Citrus sinensis (L.) Osbeck. We preferred stripping film to liquid emulsion to obtain a more uniform thickness of the silver grain layer, as this would not vary more than ±10%. Furthermore, Baserga and Nemeroff (1962) have observed a lower sensitivity of fluid emulsion in comparison to stripping film together with occasionally erratic grain count and a slightly higher incidence of mechanical fogging. However, on using the customary procedure it was found that close contact between the surface of the section and the developed emulsion was not maintained when dehydration and clearing was done in the usual manner. The following modifications were therefore introduced to prevent the formation of air pockets between these two layers.