Air Bubbles
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Author(s):  
Irina P Chubarenko

Abstract Microplastic particles (MPs, <5 mm) are found in marine ice in larger quantities than in seawater, however, the distribution pattern within the ice cores is not consistent. To get insights into the most general physical processes behind interactions of ice and plastic particles in cool natural environments, information from academic and applied research is integrated and verified against available field observations. Non-polar molecules of common-market plastics are hydrophobic, so MPs are weak ice nucleators, are repelled from water and ice, and concentrate within air bubbles and brine channels. A large difference in thermal properties of ice and plastics favours concentration of MPs at the ice surface during freeze/thaw cycles. Under low environmental temperatures, falling in polar regions below the glass / brittle-ductile transition temperatures of the common-use plastics, they become brittle. This might partially explain the absence of floating macroplastics in polar waters. Freshwater freezes at the temperature well below that of its maximum density, so the water column is stably stratified, and MPs eventually concentrate at the ice surface and in air bubbles. In contrast, below growing sea ice, mechanisms of suspension freezing under conditions of (thermal plus haline) convection should permanently entangle MPs into ice. During further sea ice growth and aging, MPs are repelled from water and ice into air bubbles, brine channels, and to the upper/lower boundaries of the ice column. Sea ice permeability, especially while melting periods, can re-distribute sub-millimeter MPs through the brine channels, thus potentially introducing the variability of contamination with time. In accord with field observations, analysis reveals several competing factors that influence the distribution of MPs in sea ice. A thorough sampling of the upper ice surface, prevention of brine leakage while sampling and handling, considering the ice structure while segmenting the ice core – these steps may be advantageous for further understanding the pattern of plastic contamination in natural ice.


2022 ◽  
Vol 12 (1) ◽  
Author(s):  
Toshiaki Nishi ◽  
Takeshi Yamaguchi ◽  
Kazuo Hokkirigawa

AbstractHigh slip-resistant footwear outsoles can reduce the risk of slip and fall on wet and icy surfaces. Falls on wet and icy surfaces can cause serious life-threatening injuries, especially for older adults. Here we show that footwear outsoles using the rubbers filled with activated carbon or sodium chloride produce higher friction force and reduce the slip rate in walking. We have identified that small depressions were formed on outsole materials filled with activated carbon or sodium chloride during friction between the rubber and surface leading to some air ingress into the interface. While there are air bubbles between the rubber and surface, real contacts are surrounded by water with negative pressure (Laplace pressure). It is considered that the negative pressure promotes real contact formation, which causes high friction. We consider that the outsole materials filled with activated carbon or sodium chloride can reduce the risk of slip-and-fall accidents.


Author(s):  
Nourhan Mortada ◽  
Annabelle Phelipot-Mardele ◽  
Christophe Lanos

Reduce the impact of the building sector has become a key point of sustainable development. The production of lightweight materials for the building industry is therefore a must. To produce such materials, foaming is a process commonly used to trap air bubbles and achieve a range of low densities. A sufficient low thermal conductivity and an acceptable ability to regulate humidity variations in order to limit overall energy consumption are the sought properties. In this study, a direct foaming method is applied to formulate gypsum foams using a commercial Plaster and two biobased foaming agents based on proteins. An anionic surfactant (α-olefin sulphonate sodium salt) is used as a reference surfactant. Varying the mixing time, protein content and water content, gypsum foams were produced. The foam volume is measured continuously during the mixing step and the foam homogeneity is controlled. The densities of fresh foams and of the hardened foams are used to identify the links between formulation and foams properties. Gypsum foam specimens with different densities ranging from 300 to 750 kg/m3 are produced. The thermal conductivity and the Moisture Buffer Value measurements are performed. Such properties appear directly linked to the porosity and pore connection of the foams. The obtained results highlight the contribution of biobased surfactant to the performance of gypsum foams.


2022 ◽  
Vol 119 (1) ◽  
pp. e2112924119
Author(s):  
Xinghua Jiang ◽  
Lucas Rotily ◽  
Emmanuel Villermaux ◽  
Xiaofei Wang

Tiny water drops produced from bubble bursting play a critical role in forming clouds, scattering sunlight, and transporting pathogens from water to the air. Bubbles burst by nucleating a hole at their cap foot and may produce jets or film drops. The latter originate from the fragmentation of liquid ligaments formed by the centripetal destabilization of the opening hole rim. They constitute a major fraction of the aerosols produced from bubbles with cap radius of curvature (R) > ∼0.4 × capillary length (a). However, our present understanding of the corresponding mechanisms does not explain the production of most submicron film drops, which represent the main number fraction of sea spray aerosols. In this study, we report observations showing that bursting bubbles with R < ∼0.4a are actually mainly responsible for submicron film drop production, through a mechanism involving the flapping shear instability of the cap with the outer environment. With this proposed pathway, the complex relations between bubble size and number of drops produced per bubble can be better explained, providing a fundamental framework for understanding the production flux of aerosols and the transfer of substances mediated by bubble bursting through the air–water interface and the sensitivity of the process to the nature of the environment.


2022 ◽  
Vol 316 ◽  
pp. 125812
Author(s):  
Tengfei Guo ◽  
Min Qiao ◽  
Xin Shu ◽  
Lei Dong ◽  
Guangcheng Shan ◽  
...  

2022 ◽  
Vol 960 (1) ◽  
pp. 012019
Author(s):  
Marilena Monica Boltinescu (Roza) ◽  
Nicolae BĂran ◽  
Albertino Giovani Roza ◽  
Mihaela Constantin

Abstract Water aeration systems are highly efficient if the dispersion of air in the water is carried out in a controlled and uniform manner. The use of fine bubble generators ensures this and in addition, creates a small loss of pressure when air passes through them. The paper demonstrates that producing as few air bubbles as possible leads to a more efficient aeration process. Two water aeration installations are compared: - The first has a perforated plate with 152 orifices Ø 0.1 mm; - The second has four perforated plates, each with 113 orifices Ø 0.05 mm; Both installations are successively supplied with the same flow rate of compressed air, at the same temperature and at the same initial dissolved oxygen concentration in the water.


2021 ◽  
Vol 14 (2) ◽  
pp. 70-74
Author(s):  
Anggrek Oktaviameta ◽  
Kardiman Kardiman ◽  
Farradina Choria Suci

Polymer Matrix Composite (PMC) is a composite material that uses a polymer matrix most widely used in industry, transportation, and everyday life. Plywood is one of the current industrial needs that is growing rapidly and is becoming a leading export. However, besides that, the availability of raw materials is decreasing along with deforestation. Resulting in the need for alternative raw materials. Straw is one of the largest wastes that is not utilized optimally. It can be used as straw as a reinforcing material for environmentally friendly composite materials. Composite material was made using the hand lay up method, with straw fiber purchased with 4% NaOH treatment using Yukalac 157 BQTN-EX unsaturated polyester resin and MEPOXE A hardener. Then, tensile testing was carried out with volume fractions of straw fiber 5%, 10% 20% and 30 % This shows that the volume fraction of straw fiber affects the strength of the composite material. The tensile strength value of the straw fiber composite meets the minimum standard for tensile strength in plywood. Judging from the surface structure of the composite material, there are voids or air bubbles. However, the most visible in the sample with fractions of 10% and 20%. Further research needs to be done with other tests such as hit test, sandpaper test to meet the requirements for SNI standard plywood.


2021 ◽  
Vol 932 ◽  
Author(s):  
Vikash Pandey ◽  
Dhrubaditya Mitra ◽  
Prasad Perlekar

We present a direct numerical simulation (DNS) study of buoyancy-driven bubbly flows in the presence of large-scale driving that generates turbulence. On increasing the turbulence intensity: (a) the bubble trajectories become more curved and (b) the average rise velocity of the bubbles decreases. We find that the energy spectrum of the flow shows a pseudo-turbulence scaling for length scales smaller than the bubble diameter and a Kolmogorov scaling for scales larger than the bubble diameter. We conduct a scale-by-scale energy budget analysis to understand the scaling behaviour observed in the spectrum. Although our bubbles are weakly buoyant, the statistical properties of our DNS are consistent with the experiments that investigate turbulence modulation by air bubbles in water.


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