Atomization dynamics of binary droplet on oil pool driven by the Marangoni effect

The Marangoni effect on the critical heat flux (CHF) condition in pool boiling of binary mixtures has been identified and its effect has been quantitatively estimated with a modified model derived from hydrodynamics. The physical process of CHF in binary mixtures, and models used to describe it, are examined in the light of recent experimental evidence, accurate mixture properties, and phase equilibrium revealing a correlation to surface tension gradients and volatility. A correlation is developed from a heuristic model including the additional liquid restoring force caused by surface tension gradients. The CHF condition was determined experimentally for saturated methanol/water, 2-propanol/water, and ethylene glycol/water mixtures, over the full range of concentrations, and compared to the model. The evidence in this study demonstrates that in a mixture with large differences in surface tension, there is an additional hydrodynamic restoring force affecting the CHF condition.

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Engineering motile aqueous phase-separated droplets via liposome stabilisation

Nature Communications ◽

10.1038/s41467-021-21832-x ◽

2021 ◽

Vol 12 (1) ◽

Author(s):

Shaobin Zhang ◽

Claudia Contini ◽

James W. Hindley ◽

Guido Bolognesi ◽

Yuval Elani ◽

...

Keyword(s):

Aqueous Phase ◽

Marangoni Effect ◽

Living Systems ◽

Biological Processes ◽

Biological Applications ◽

Emulsion System ◽

Biotechnological Potential ◽

New Directions ◽

Directional Motion ◽

The Stability

AbstractThere are increasing efforts to engineer functional compartments that mimic cellular behaviours from the bottom-up. One behaviour that is receiving particular attention is motility, due to its biotechnological potential and ubiquity in living systems. Many existing platforms make use of the Marangoni effect to achieve motion in water/oil (w/o) droplet systems. However, most of these systems are unsuitable for biological applications due to biocompatibility issues caused by the presence of oil phases. Here we report a biocompatible all aqueous (w/w) PEG/dextran Pickering-like emulsion system consisting of liposome-stabilised cell-sized droplets, where the stability can be easily tuned by adjusting liposome composition and concentration. We demonstrate that the compartments are capable of negative chemotaxis: these droplets can respond to a PEG/dextran polymer gradient through directional motion down to the gradient. The biocompatibility, motility and partitioning abilities of this droplet system offers new directions to pursue research in motion-related biological processes.

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Comparison of fire extinguishing performance of four halon substitutes and Halon 1301

Journal of Fire Sciences ◽

10.1177/07349041211030188 ◽

2021 ◽

pp. 073490412110301

Author(s):

Yawei Wang ◽

Gaowan Zou ◽

Conglin Liu ◽

Y Gao

Keyword(s):

Dilution Effect ◽

Pool Fire ◽

Design Standards ◽

Ignition Probability ◽

Fire Extinguishing ◽

Halon 1301 ◽

Efficient Alternative ◽

Oil Pool ◽

The Difference ◽

Effect Of Oxygen

The Halon 1301 fixed gas fire extinguishing system used in ship engine rooms has been banned from production all over the world, because halon destroys the ozone layer. Therefore, it is necessary to find an environmentally friendly, compatible and efficient alternative firefighting system. In this study, we performed fire extinguishing tests in an ISO9705 standard room for four alternative fire extinguishing agents, as well as Halon 1301. The fire extinguishing efficiency of each agent was determined based on its cooling effect, dilution effect of oxygen concentration, the extinguishing time of the oil pool fire and the re-ignition probability of the wood stack. The test results provide data support for the selection of alternatives of Halon 1301 from the aspect of fire extinguishing efficiency. Among these results, Novec 1230 had the best ability to put out the oil pool fire, and HFC-227ea suppressed the wood stack fire the best. The difference between the cooling ability of each fire extinguishing agent was small, and the inert gas (IG-541) displayed the best ability to dilute oxygen. Hot aerosol required the longest time to extinguish fire. Consequently, under the existing design standards, HFC-227ea had the better firefighting efficiency, more suitable to replace Halon 1301.

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CFD-based modelling of phase transformation in laser welded low-carbon steel

Welding in the World ◽

10.1007/s40194-021-01130-2 ◽

2021 ◽

Author(s):

Aleksander Siwek

Keyword(s):

Heat Source ◽

Phase Transformations ◽

Power Distribution ◽

Low Carbon Steel ◽

Marangoni Effect ◽

Phase Changes ◽

Test Material ◽

Low Carbon ◽

Welding Condition ◽

Welding Pool

AbstractThis paper presents a numerical model of the laser welding of steel, taking into account the heat and mass flows, as well as thermal effects associated with phase transformations. It was assumed that the heat source is a laser with a symmetrical power distribution of the TEM10 beam in two welding condition variants: a stationary heat source and a source moving at a constant speed along the sample. After reaching the melting temperature, the movement of the liquid phase was forced by the Marangoni effect acting on the surface of the welding pool. For the laser power applied, the surface of the welding pool was assumed to be flat. It was proposed an algorithm for the forecasting of the phase changes during heating and cooling. Diffusive phase transformations during cooling were modelled using Johnson-Mehl-Avrami-Kolmogorov (JMAK) equations. Diffusionless transformations occurring when cooling rates exceed the critical ones were modelled using Koistinen-Marburger (KM) equations. Calculations were made for a rectangular sample welded in air and cooled spontaneously in the atmosphere. The boundary conditions were simulated assuming a constant coefficient of heat exchange and radiation to the environment. The start and end time of the changes occurring in the cooling phase were calculated based on the average cooling rate in the temperature range 800–500°C (v8/5). The model was tested for the test material: S355J2 steel.

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